Andrea Luigi CARDINI - personale UniMoRe

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Andrea Luigi CARDINI

Ricercatore Universitario
Dipartimento di Scienze Chimiche e Geologiche - Sede Dipartimento di Scienze Chimiche e Geologiche

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Pubblicazioni

2023 - Do brachycephaly and nose size predict the severity of obstructive sleep apnea (OSA)? A sample-based geometric morphometric analysis of craniofacial variation in relation to OSA syndrome and the role of confounding factors [Articolo su rivista]
Daboul, Amro; Krüger, Markus; Ivanonvka, Tatyana; Obst, Anne; Ewert, Ralf; Stubbe, Beate; Fietze, Ingo; Penzel, Thomas; Hosten, Norbert; Biffar, Reiner; Cardini, Andrea
abstract

Obstructive sleep apnea is a common disorder that leads to sleep fragmentation and is potentially bidirectionally related to a variety of comorbidities, including an increased risk of heart failure and stroke. It is often considered a consequence of anatomical abnormalities, especially in the head and neck, but its pathophysiology is likely to be multifactorial in origin. With geometric morphometrics, and a large sample of adults from the Study for Health in Pomerania, we explore the association of craniofacial morphology to the apnea–hypopnea index used as an estimate of obstructive sleep apnea severity. We show that craniofacial size and asymmetry, an aspect of morphological variation seldom analysed in obstructive sleep apnea research, are both uncorrelated to apnea–hypopnea index. In contrast, as in previous analyses, we find evidence that brachycephaly and larger nasal proportions might be associated to obstructive sleep apnea severity. However, this correlational signal is weak and completely disappears when age-related shape variation is statistically controlled for. Our findings suggest that previous work might need to be re-evaluated, and urge researchers to take into account the role of confounders to avoid potentially spurious findings in association studies.

2022 - As fast as a hare: Did intraspecific morphological change bring the Hallands Väderö Island population of Lepus timidus close to interspecific differences in less than 150 years? [Articolo su rivista]
Cardini, A.
abstract

: The study of insular variation has fascinated generations of biologists and has been central to evolutionary biology at least since the time of Wallace and Darwin. In this context, using 3D geometric morphometrics, I investigate whether the population of mountain hares (Lepus timidus Linnaeus, 1758) introduced in 1857 on the Swedish island of Hallands Väderö shows distinctive traits in cranial size and shape. I find that size divergence follows the island rule, but is very small. In contrast, shape differences, compared to the mainland population, are almost as large as interspecific differences among lineages separated by hundreds of thousands of years of a largely independent evolutionary history. Even if, contrary to what is documented in the scientific literature, mountain hares were present in HV before 1857, the evolutionary history of this population could not have start earlier than the end of the last glaciation (i.e., at least one order of magnitude more recently than the separation of L. timidus from other hare species in this study). My results, thus, suggest that the insular population is a significant evolutionary unit and a potentially important component of the diversity of Swedish mountain hares. This is interesting for evolutionary biologists, but even more relevant for conservationists trying to protect the disappearing population of southern Swedish L. timidus, threatened by changes in climate and the environment, as well as by disease and the introduced European hare (Lepus europaeus Pallas, 1778). Island populations of mountain hares, thus, represent a potential source for future reintroductions on the mainland and, as my research shows, an important component of variability to maximize the preservation of the evolutionary potential in a species facing huge environmental changes.

2022 - Can morphotaxa be assessed with photographs? Estimating the accuracy of two-dimensional cranial geometric morphometrics for the study of threatened populations of African monkeys [Articolo su rivista]
Cardini, A.; de Jong, Y. A.; Butynski, T. M.
abstract

The classification of most mammalian orders and families is under debate and the number of species is likely greater than currently recognized. Improving taxonomic knowledge is crucial, as biodiversity is in rapid decline. Morphology is a source of taxonomic knowledge, and geometric morphometrics applied to two dimensional (2D) photographs of anatomical structures is commonly employed for quantifying differences within and among lineages. Photographs are informative, easy to obtain, and low cost. 2D analyses, however, introduce a large source of measurement error when applied to crania and other highly three dimensional (3D) structures. To explore the potential of 2D analyses for assessing taxonomic diversity, we use patas monkeys (Erythrocebus), a genus of large, semi-terrestrial, African guenons, as a case study. By applying a range of tests to compare ventral views of adult crania measured both in 2D and 3D, we show that, despite inaccuracies accounting for up to one-fourth of individual shape differences, results in 2D almost perfectly mirror those in 3D. This apparent paradox might be explained by the small strength of covariation in the component of shape variance related to measurement error. A rigorous standardization of photographic settings and the choice of almost coplanar landmarks are likely to further improve the correspondence of 2D to 3D shapes. 2D geometric morphometrics is, thus, appropriate for taxonomic comparisons of patas ventral crania. Although it is too early to generalize, our results corroborate similar findings from previous research in mammals, and suggest that 2D shape analyses are an effective heuristic tool for morphological investigation of small differences.

2022 - Procrustes Shape Cannot be Analyzed, Interpreted or Visualized one Landmark at a Time [Articolo su rivista]
Cardini, A.; Marco, V. A.
abstract

Landmark-based geometric morphometrics using the Procrustes approach has become the dominant family of methods in morphometrics. However, the superimposition (and sliding, if semilandmarks are present), that transforms raw coordinates into shape coordinates is biologically arbitrary. Procrustes has desirable statistical properties, but is not based on a biological model. The same is true for sliding methods. These techniques allow powerful statistical analyses of a full set of shape coordinates, but make the use of subsets of landmarks/semilandmarks problematic, inaccurate and misleading, if not totally wrong. Crucially, the biological arbitrariness of the superimposition prevents any meaningful quantification, analysis and interpretation of variation one landmark/semilandmark at a time. We exemplify how misleading this type of analyses can be by using a real dataset, as well as simulated data with isotropic variation. Both show inconsistencies in ‘per-landmark/semilandmark’ variances. The simulation in fact helps to make even more obvious that the pattern of variance is strongly influenced by the biologically arbitrary choice of the mathematical treatment. Unfortunately, despite this limitation of all superimposition methods being known since the early days of Procrustean morphometrics, there has been a recent series of papers in leading journals presenting results of ‘per-landmark’ analyses. Thus, we further clarify why these analyses are wrong and represent misleading examples that should not be followed: Procrustes shape data cannot be analyzed, visualized or interpreted one landmark at a time. For users who are in doubt, in the Conclusions, we provide a short list of recommendations on how to easily avoid this type of mistakes.

2022 - Rosling’s fallacy: Conservation, biodiversity and the anthropocentrism of Hans Rosling’s Factfulness [Articolo su rivista]
Cardini, Andrea Luigi
abstract

2021 - Corrigendum to “How flat can a horse be? Exploring 2D approximations of 3D crania in equids” [Zoology 139 (2020) 125746] (Zoology (2020) 139, (S0944200620300052), (10.1016/j.zool.2020.125746)) [Articolo su rivista]
Cardini, A.; Chiapelli, M.
abstract

The authors regret that the F ratios reported in Table 5 were incorrect. The erroneous Fs, however, have similar P values and therefore do not change the interpretation of results. Also, the factor below “individuals” is “measurement error” in Table 5 and should be “residuals” in Table 3A-B (i.e., the correct name for these rows were by mistake swapped in the two tables). The correct table 5 is reproduced directly below. Tab. 5. ANOVA in common data space at micro- (A) and macro-evolutionary (B) levels. [Table presented] The authors would like to apologise for any inconvenience caused.

2021 - On the Misidentification of Species: Sampling Error in Primates and Other Mammals Using Geometric Morphometrics in More Than 4000 Individuals [Articolo su rivista]
Cardini, A.; Elton, S.; Kovarovic, K.; Strand Vidarsdottir, U.; Polly, P. D.
abstract

An accurate classification is the basis for research in biology. Morphometrics and morphospecies play an important role in modern taxonomy, with geometric morphometrics increasingly applied as a favourite analytical tool. Yet, really large samples are seldom available for modern species and even less common in palaeontology, where morphospecies are often identified, described and compared using just one or a very few specimens. The impact of sampling error and how large a sample must be to mitigate the inaccuracy are important questions for morphometrics and taxonomy. Using more than 4000 crania of adult mammals and taxa representing each of the four placental superorders, we assess the impacts of sampling error on estimates of species means, variances and covariances in Procrustes shape data using resampling experiments. In each group of closely related species (mostly congeneric), we found that a species can be identified fairly accurately even when means are based on relatively small samples, although errors are frequent with fewer specimens and primates more prone to inaccuracies. A precise reconstruction of similarity relationships, in contrast, sometimes requires very large samples (> 100), but this varies widely depending on the study group. Medium-sized samples are necessary to accurately estimate standard errors of mean shapes or intraspecific variance covariance structure, but in this case minimum sample sizes are broadly similar across all groups (≈ 20–50 individuals). Overall, thus, the minimum sample sized required for a study varies across taxa and depends on what is being assessed, but about 25–40 specimens (for each sex, if a species is sexually dimorphic) may be on average an adequate and attainable minimum sample size for estimating the most commonly used shape parameters. As expected, the best predictor of the effects of sampling error is the ratio of between- to within-species variation: the larger the ratio, the smaller the sample size needed to obtain the same level of accuracy. Even though ours is the largest study to date of the uncertainties in estimates of means, variances and covariances in geometric morphometrics, and despite its generally high congruence with previous analyses, we feel it would be premature to generalize. Clearly, there is no a priori answer for what minimum sample size is required for a particular study and no universal recipe to control for sampling error. Exploratory analyses using resampling experiments are thus desirable, easy to perform and yield powerful preliminary clues about the effect of sampling on parameter estimates in comparative studies of morphospecies, and in a variety of other morphometric applications in biology and medicine. Morphospecies descriptions are indeed a small piece of provisional evidence in a much more complex evolutionary puzzle. However, they are crucial in palaeontology, and provide important complimentary evidence in modern integrative taxonomy. Thus, if taxonomy provides the bricks for accurate research in biology, understanding the robustness of these bricks is the first fundamental step to build scientific knowledge on sound, stable and long-lasting foundations.

2021 - Sexual differences in human cranial morphology: Is one sex more variable or one region more dimorphic? [Articolo su rivista]
Milella, M.; Franklin, D.; Belcastro, M. G.; Cardini, A.
abstract

The quantification of cranial sexual dimorphism (CSD) among modern humans is relevant in evolutionary studies of morphological variation and in a forensic context. Despite the abundance of quantitative studies of CSD, few have specifically examined intra-sex variability. Here we quantify CSD in a geographically homogeneous sample of adult crania, which includes Italian individuals from the 19th and 20th centuries. Cranial morphology is described with 92 3D landmarks analyzed using Procrustean geometric morphometrics (PGMM). Size and shape variables are used to compare morphological variance between sexes in the whole cranium and four individual regions. The same variables, plus Procrustes form, are used to quantify average sex differences and explore classification accuracy. Our results indicate that: (a) as predicted by Wainer's rule, males present overall more variance in size and shape, albeit this is statistically significant only for total cranial size; (b) differences between sexes are dominated by size and to a lesser extent by Procrustes form; (c) shape only accounts for a minor proportion of variance; (d) the cranial base shows almost no dimorphism for shape; and (e) facial Procrustes form is the most accurate predictor of skeletal sex. Overall, this study suggests developmental factors underlying differences in CSD among cranial regions; stresses the need for population-specific models that describe craniofacial variation as the basis for models that facilitate the estimation of sex in unidentified skeletal remains; and provides one of the first confirmations of “Wainer's rule” in relation to sexual dimorphism in mammals specific to the human cranium.

2021 - The pangolin is not the culprit and species do not mount invasions [Articolo su rivista]
Cardini, Andrea
abstract

2020 - Cross-validated Between Group PCA Scatterplots: A Solution to Spurious Group Separation? [Articolo su rivista]
Cardini, Andrea; Polly, P. David
abstract

https://link.springer.com/article/10.1007/s11692-020-09494-x

2020 - How flat can a horse be? Exploring 2D approximations of 3D crania in equids [Articolo su rivista]
Cardini, Andrea; Chiapelli, Marika
abstract

https://www.sciencedirect.com/science/article/pii/S0944200620300052

2020 - Less tautology, more biology? A comment on “high-density” morphometrics [Articolo su rivista]
Cardini, A.
abstract

In the context of geometric morphometric analyses of modularity and integration using Procrustes methods, some researchers have recently claimed that “high-density geometric morphometric data exceed the traditional landmark-based methods in the characterization of morphology and allow more nuanced comparisons across disparate taxa” and also that, using “high-density” data (i.e., with dozens or hundreds of semilandmarks), “potential issues [with tests of modularity and integration] are unlikely to obscure genuine biological signal”. I show that the first claim is invalidly tautological and, therefore, flawed, while the second one is a speculation. “High-density” geometric morphometrics is a potentially useful tool for the quantification of continuous morphological variation in evolutionary biology, but cannot be said to represent absolute accuracy, simply because more measurements increase information, but do not by default imply that this information is accurate. Semilandmarks are an analytical expedient to break the continuity of regions devoid of clearly corresponding landmarks, but the shape variables which they generate are a function of the specific choice of the placement and possible mathematical manipulation of these points. Not only there are infinite ways of splitting a curve or surface into discrete points, but also none of the methods to slide the semilandmarks increases the accuracy of their mapping onto the underlying biological homology: indeed, none of them is based on a biological model, and the assumption of universal equivalence between geometric and biological correspondence is unverified, if at all verifiable. Besides, in the specific context of modularity and integration using Procrustes geometric morphometrics, the limited number of scenarios simulated until now may provide interesting clues, but do not yet allow strong statements and clear generalizations. The Procrustes superimposition does alter the ‘true’ covariance structure of the data and sliding semilandmarks further contributes to this change. Although we hope that this might only add a negligible source of inaccuracy, and simulations using landmarks (but no semilandmarks yet) suggest that this might be the case, it is too early to confidently share the view, expressed by the promoters of high-density methods, that this is “Not-Really-a-Problem”. The evidence is very preliminary and the dichotomy may not be this simple, with the magnitude (from negligible to large) and direction (inflation of modularity, integration, or both) of a potential bias in the tests likely to vary in ways specific to the data being analysed. We need more studies that provide robust and generalizable evidence, without indulging in invalid tautology and over-interpretation. With both landmarks and semilandmarks, what is measured should be functional to the specific hypothesis and we should be clear on where the treatment of the data is pure mathematics and where there is a biological model that supports the maths.

2020 - Modern morphometrics and the study of population differences: Good data behind clever analyses and cool pictures? [Articolo su rivista]
Cardini, A.
abstract

The study of phenotypic variation in time and space is central to evolutionary biology. Modern geometric morphometrics is the leading family of methods for the quantitative analysis of biological forms. This set of techniques relies heavily on technological innovation for data acquisition, often in the form of 2D or 3D digital images, and on powerful multivariate statistical tools for their analysis. However, neither the most sophisticated device for computerized imaging nor the best statistical test can produce accurate, robust and reproducible results, if it is not based on really good samples and an appropriate use of the ‘measurements’ extracted from the data. Using examples mostly from my own work on mammal craniofacial variation and museum specimens, I will show how easy it is to forget these most basic assumptions, while focusing heavily on analytical and visualization methods, and much less on the data that generate potentially powerful analyses and visually appealing diagrams.

2019 - Craniofacial Allometry is a Rule in Evolutionary Radiations of Placentals [Articolo su rivista]
Cardini, Andrea Luigi
abstract

2019 - Geometric morphometrics on juvenile crania: Exploring age and sex variation in an Australian population [Articolo su rivista]
Noble, Jacqueline; Cardini, Andrea; Flavel, Ambika; Franklin, Daniel
abstract

2019 - Integration and Modularity in Procrustes Shape Data: Is There a Risk of Spurious Results? [Articolo su rivista]
Cardini, Andrea
abstract

2019 - Seeing Distinct Groups Where There are None: Spurious Patterns from Between-Group PCA [Articolo su rivista]
Cardini, Andrea; O’Higgins, Paul; Rohlf, F. James
abstract

Using sampling experiments, we found that, when there are fewer groups than variables, between-groups PCA (bgPCA) may suggest surprisingly distinct differences among groups for data in which none exist. While apparently not noticed before, the reasons for this problem are easy to understand. A bgPCA captures the g − 1 dimensions of variation among the g group means, but only a fraction of the ∑ ni- g dimensions of within-group variation (ni are the sample sizes), when the number of variables, p, is greater than g − 1. This introduces a distortion in the appearance of the bgPCA plots because the within-group variation will be underrepresented, unless the variables are sufficiently correlated so that the total variation can be accounted for with just g − 1 dimensions. The effect is most obvious when sample sizes are small relative to the number of variables, because smaller samples spread out less, but the distortion is present even for large samples. Strong covariance among variables largely reduces the magnitude of the problem, because it effectively reduces the dimensionality of the data and thus enables a larger proportion of the within-group variation to be accounted for within the g − 1-dimensional space of a bgPCA. The distortion will still be relevant though its strength will vary from case to case depending on the structure of the data (p, g, covariances etc.). These are important problems for a method mainly designed for the analysis of variation among groups when there are very large numbers of variables and relatively small samples. In such cases, users are likely to conclude that the groups they are comparing are much more distinct than they really are. Having many variables but just small sample sizes is a common problem in fields ranging from morphometrics (as in our examples) to molecular analyses.

2019 - “Nose-metrics” of wild southern elephant seal (Mirounga leonina) males using image analysis and geometric morphometrics [Articolo su rivista]
Galimberti, Filippo; Sanvito, Simona; Vinesi, Maria Chiara; Cardini, Andrea
abstract

2018 - Erratum to: Larger mammals have longer faces because of size-related constraints on skull form (Nature Communications, (2013), 4, 1, (2458), 10.1038/ncomms3458) [Articolo su rivista]
Cardini, A.; Polly, P. D.
abstract

In Table 1 of this article, the descriptions of landmarks 14, 15, and 36 are incorrect. Landmarks 14 and 36 should read “Posterior extremity of occipital condyle along margin of foramen magnum” and landmark 15 should read “Opisthion”. A correct version of Table 2 appears in the Author Correction associated with this article; the error has not been fixed in the original article.

2018 - Procrustes-based geometric morphometrics on MRI images: An example of inter-operator bias in 3D landmarks and its impact on big datasets [Articolo su rivista]
Daboul, Amro; Ivanovska, Tatyana; Bülow, Robin; Biffar, Reiner; Cardini, Andrea
abstract

2017 - Anyone with a Long-Face? Craniofacial Evolutionary Allometry (CREA) in a Family of Short-Faced Mammals, the Felidae [Articolo su rivista]
Tamagnini, Davide; Meloro, Carlo; Cardini, Andrea
abstract

https://link.springer.com/article/10.1007/s11692-017-9421-z

2017 - Estimating the magnitude of morphoscapes: how to measure the morphological component of biodiversity in relation to habitats using geometric morphometrics [Articolo su rivista]
Fontaneto, D; Panisi, M; Mandrioli, Mauro; Montardi, Dario; Pavesi, M; Cardini, Andrea Luigi
abstract

Ecological indicators are currently developed to account for the different facets of loss of biological diversity due to direct or indirect effects of human activities. Most ecological indicators include species richness as a metric. Others, such as functional traits and phylogenetic diversity, account for differences in species, even when species richness is the same. Here, we describe and apply a different indicator, called morphoscape dimension, accounting for morphological variability across habitats in a geographical region. We use the case of ground beetles (Coleoptera: Carabidae) in four different habitats in the Po Plain in Northern Italy to exemplify how to quantify the magnitude of the morphological space (i.e. the dimension of the morphoscape) occupied by the species in each habitat using geometric morphometrics. To this aim, we employed a variety of metrics of morphological disparity related to univariate size, and more complex multivariate shape and form. Our ‘proof of concept’ suggests that metrics assessing size and form might largely tend to simply mirror the information provided by species richness, whereas shape morphoscape disparity may be able to account for non-trivial differences in species traits amongst habitats. This is indicated by the woodland morphoscape being on average bigger than that of crops, the most species-rich habitat, despite having almost 20% less species. We conclude suggesting that the analysis of morphoscape dimension has the potential to become a new additional and complimentary tool in the hands of conservation biologists and ecologists to explore and quantify habitat complexity and inform decisions on management and conservation based on a wide set of ecological indicators.

2017 - Is there a 'Wainer's rule'? Testing which sex varies most as an example analysis using GueSDat, the free Guenon Skull Database [Articolo su rivista]
Cardini, Andrea Luigi; Elton, Sarah
abstract

SUMMARY - The distinguished statistician Howard Wainer claimed that larger phenotypic variance in males might be a general occurrence in mammals. We called this putative pattern 'Wainer's rule' and employed a dataset of more than 1300 specimens, each measured using 86 anatomical landmarks on skulls, to test this hypothesis using size and shape data in a group of Old World monkeys, the guenons. Our study is one example of an application that takes advantage of this large set of data (named ‘GueSDat’), made freely available to the research community. The analysis showed that large samples are crucial to estimate variances, and, in this respect, estimates of univariate size may require even larger samples than estimates of the magnitude of shape variance. Despite limited statistical power in species with smaller samples, results consistently suggest larger variance in male skull size but not in shape. Size could be more plastic and thus respond more directly to the environment. As males are larger than females, the costs of becoming bigger can be sustained only when conditions are optimal, thus making size strongly condition dependant and therefore more variable in the bigger sex. However, it is not only overall size and shape that may behave differently in terms of whether they follow 'Wainer's rule': preliminary analyses suggest that, as in insects, different traits (e.g., different cranial regions) may vary in how similar or different their phenotypic variance is. The example study shows the potentially wide applications of data in GueSDat and suggests that, besides the most common comparison of mean differences in females and males, the study of differences between sexes in phenotypic variance offers a promising avenue for future research in mammals. Indeed, as exemplified by our work, testing 'Wainer's rule' in mammals and other animals could become an active field of investigation in a variety of disciplines (from morphological to behavioural studies), and one that will hopefully elucidate whether this trend might be so common to be considered as a 'rule' in evolutionary biology.

2017 - Left, right or both? Estimating and improving accuracy of one-side-only geometric morphometric analyses of cranial variation [Articolo su rivista]
Cardini, Andrea Luigi
abstract

Procrustes-based geometric morphometric analyses of bilaterally symmetric structures are often performed using only one side. This is particularly common in studies of cranial variation in mammals and other vertebrates. When one is not interested in quantifying asymmetry, landmarking one side, instead of both, reduces the number of variables as well as the time and costs of data collection. It is assumed that the loss of information in the other half, on which landmarks are not digitized, is negligible, but this has seldom been tested. Using 10 samples of mammalian crania and a total of more than 500 specimens, and five different landmark configurations, I demonstrate that this assumption is indeed easily met for size. For shape, in contrast, one-side landmarking has potentially more severe consequences on the estimates of similarity relationships in a sample. In this respect, microevolutionary analyses of small differences are particularly affected, whereas macroevolutionary studies are fairly robust. In almost all instances, however, a simple preliminary operation improves accuracy by making one-side-only shape data more similar to those obtained by landmarking both sides. The same operation also makes estimates of allometry more accurate and improves the visualization. This operation consists in estimating the missing side by a mirror reflection of bilateral landmarks. In the Supporting Information, I exemplify how this can be easily done using free user-friendly software. I also provide an example data set for readers to repeat and learn the steps of this simple procedure.

2017 - Shape variation of prey-catching structures in geophilomorph centipedes: A preliminary investigation using geometric morphometrics [Articolo su rivista]
Baiocco, Matteo; Bonato, Lucio; Cardini, Andrea Luigi; Fusco, Giuseppe
abstract

Geophilomorph centipedes are common arthropod soil predators, but very little is known about their preying behaviour and their diet. Here we develop an exploratory morpho-functional approach to better understand their feeding habits, based on the morphology of feeding-related structures. Through geometric morphometrics, in a sample of five geophilomorph species, we investigated morphological variation in the three most conspicuous component structures of their prey-catching apparatus. At intra-specific level, we found no strong evidence for sexual dimorphism, left-right directional asymmetries and allometry across adult stages. At inter-specific level, shape differences in the feeding apparatus among the sample species were highly significant and large, even between two congeneric species. We also found a significant covariation between the shapes of the three structures, including those that do not directly articulate with each other, suggesting some degree of morphological integration between the different structures of the prey-catching apparatus. This study suggests the effectiveness and power of geometric morphometrics for the quantitative study of centipede functional morphology and provides a basis for wider comparative investigations on their phenotypic evolution.

2016 - A ‘long-fuse domestication’ of the horse? Tooth shape suggests explosive change in modern breeds compared with extinct populations and living Przewalski’s horses [Articolo su rivista]
Seetah, Krish; Cardini, Andrea Luigi; Barker, Graeme
abstract

Archaeological and molecular data suggest that horses were domesticated comparatively recently, the genetic evidence indicating that this was from several maternal haplotypes but only a single paternal one. However, although central to our understanding of how humans and environmental conditions shaped animals during domestication, the phenotypic changes associated with this idiosyncratic domestication process remain unclear. Using geometric morphometrics on a sample of horse teeth including Pleistocene wild horses, modern Icelandic and Thoroughbred domestic horses, Przewalski’s wild horses of recent age and domestic horses of different ages through the Holocene, we show that, despite variations in size likely related to allometry (changes to bone size in proportion to body size), natural and artificial selective pressures and geographic and temporal heterogeneity, the shape of horse teeth has changed surprisingly little over thousands of years across Eurasia: the shapes of the premolars of prehistoric and historic domestic horses largely resemble those of Pleistocene and recent wild horses. However, this changed dramatically after the end of the Iron Age with an explosive increase in the pace and scale of variation in the past two millennia, ultimately resulting in a twofold jump in the magnitude of shape divergence in modern breeds. Our findings indicate that the pace of change during domestication may vary even within the same structure with shape, but not size, suggesting a ‘long-fuse’ model of phenotypic modification, where an initial lengthy period of invariance is followed by an explosive increase in the phenotypic change. These observations support a testable model that is applicable to other traits and species and add a new layer of complexity to the study of interactions between humans and the organisms they domesticated.

2016 - Lost in the Other Half: Improving Accuracy in Geometric Morphometric Analyses of One Side of Bilaterally Symmetric Structures [Articolo su rivista]
Cardini, Andrea Luigi
abstract

Systematists and evolutionary biologists have widely adopted Procrustes-based geometric morphometrics for measuring size and shape in biology. Many structures, and in fact most animals, are bilaterally symmetric with an internal plane of symmetry (also called object symmetry). Often, when quantifying asymmetric variation is not an aim, only one or the other side is measured and analyzed. This approach has been used in hundreds of studies. Its implicit assumption is that the information on the other side is redundant and a single side will, therefore, produce results mirroring those one would have obtained from the analysis of the entire structure with all its left and right landmarks. However, the extent to which this assumption is met has, to my knowledge, never been explored. Using two example data sets, I will show that congruence may be high in analyses at a macroevolutionary level but much lower at a microevolutionary one, and inaccuracies might especially affect shape. I will discuss some of the other factors that may influence results and will suggest a simple expedient that can improve both the visualization and accuracy of shape analyses in one-side-only studies.

2015 - Bioturbation beyond Earth: potential, methods and models of astroichnology [Abstract in Atti di Convegno]
Baucon, Andrea; de Carvalho, Carlos Neto; Bernardini, Federico; Cardini, Andrea Luigi; Cavalazzi, Barbara; Celani, Antonio; Felletti, Fabrizio; Ferretti, Annalisa; Schönlaub, Hans Peter; Todaro, Mary Antonio Donatello
abstract

Traces – burrows, borings, footprints – are important evidences of biological behaviour on Earth, yet they received relatively little attention in the field of astrobiology. This study aims to discuss the application of ichnology (i.e. the study of life activity traces) to the search for past and modern life beyond Earth (i.e. herein called Astroichnology).

2015 - How many specimens do I need? Sampling error in geometric morphometrics: testing the sensitivity of means and variances in simple randomized selection experiments [Articolo su rivista]
Cardini, Andrea Luigi; Seetah, Krish; Barker, Graeme
abstract

One of the most basic but problematic issues in modern morphometrics is how many specimens one needs to achieve accuracy in samples. Indeed, this is one of the most regularly posed questions in introductory courses. There is no simple and certainly no absolute answer to this question. However, there are a number of techniques for exploring the effect of sampling, and our aim is to provide an example of how this might function in a simplified but informative way. Thus, using resampling methods and sensitivity analyses based on randomized subsamples, we assessed sampling error in horse teeth from several modern and fossil populations. Centroid size and shape of an upper premolar (PM2) were captured using Procrustes geometric morphometrics. Means and variances (using three different statistics for shape variance) were estimated, as well as their confidence intervals. Also, the largest population sample was randomly split into progressively smaller subsamples to assess how reducing sample size affects statistical parameters. Results indicate that mean centroid size is highly accurate; even when sample size is small, errors are generally considerably smaller than differences among populations. In contrast, mean shape estimation requires large samples of tens of specimens (ca. >20), although this requirement may be less stringent when variance in a population is very small (e.g. populations that underwent strong genetic bottlenecks). Variance in either centroid size or shape can be highly inaccurate in small samples, to the point that sampling error makes it as variable as differences among spatially and chronologically well-separated populations, including two which are highly distinctive as a consequence of strong artificial selection. Likely, centroid size and shape variance require no <15–20 specimens to achieve a reasonable degree of accuracy. Results from the simplified sensitivity analysis were largely congruent with the pattern suggested by bootstrapped confidence intervals, as well as with the observations of a previous study on African monkeys. The analyses we performed, especially the sensitivity assessment, are simple and do not require much time or computational effort; however, they do necessitate that at least one sample is large (50 or more specimens). If this type of analyses became more common in geometric morphometrics, it could provide an effective tool for the preliminarily exploration of the effect of sampling on results and therefore assist in assessing their robustness. Finally, as the use of sensitivity studies increases, the present case could form part of a set of examples that allow us to better understand and estimate what a desirable sample size might be, depending on the scientific question, type of data and taxonomic level under investigation.

2015 - Marmot evolution and global change in the past 10 million years [Capitolo/Saggio]
Polly, P. David; Cardini, Andrea Luigi; Davis, Edward B.; Steppan, Scott J.
abstract

Ground squirrels of the genus Marmota are known for their ability to tolerate bitterly cold climates, which they in part accomplish with their exceptional ability to hibernate for as much as eight months a year (Armitage et al., 2003). Most of the 15 living species are associated with montane habitats, and those that are not, like the North American woodchuck (Marmota monax) and the eastern European and central Asian bobak (M. bobak) inhabit regions with strongly seasonal climates and often bitterly cold winters (Armitage, 2000) (Figure 9.1). All marmots construct burrows, which can be more than one metre deep even in comparatively mild climates and as much as seven metres deep in the harsh climates of the Himalayas (Barash, 1989). During the cold phases of the last half of the Quaternary the fossil record demonstrates many marmots inhabited periglacial environments (Zimina and Gerasimov, 1973; Kalthoff, 1999). For these reasons, marmots are sometimes considered to be a quintessentially Quaternary clade, specialists on the cold variable climates that are unique to the past 2.6 million years of Earth's history. The world in which they originated, however, was very different; a warmer one in which there were no tundra biomes, no glacial–interglacial cycles, and no permanent ice cover in the Northern Hemisphere. In this chapter, we review the fossil and phylogenetic history of marmots, the palaeoenvironments in which they originated, and their relationship to glacial–interglacial cycles to better understand the contexts in which the specializations of this unique clade of rodents arose. ...

2015 - Piracy strikes back on Lake Maggiore (Northen Italy): first report of Common Merganser Mergus merganser kleptoparasitizing Great Crested grebe Podiceps cristatus [Articolo su rivista]
Cardini, Andrea Luigi; Chiozzi, Giorgio
abstract

Not available

2015 - The 'temporal effect' in hominids: Reinvestigating the nature of support for a chimp-human clade in bone morphology [Articolo su rivista]
Pearson, Alannah; Groves, Colin; Cardini, Andrea Luigi
abstract

In 2004, an analysis by Lockwood and colleagues of hard-tissue morphology, using geometric morphometrics on the temporal bone, succeeded in recovering the correct phylogeny of living hominids without resorting to potentially problematic methods for transforming continuous shape variables into meristic characters. That work has increased hope that by using modern analytical methods and phylogenetically informative anatomical data we might one day be able to accurately infer the relationships of hominins, including the closest extinct relatives of modern humans. In the present study, using 3D virtually generated models of the hominid temporal bone and a larger suite of geometric morphometric and comparative techniques, we have re-examined the evidence for a Pan-Homo clade. Despite differences in samples, as well as the type of raw data, the effect of measurement error (and especially landmark digitization by a different operator), but also a broader perspective brought in by our diverse set of approaches, our reanalysis largely supports Lockwood and colleagues' original results. However, by focusing not only mainly on shape (as in the original 2004 analysis) but also on size and 'size-corrected' (non-allometric) shape, we demonstrate that the strong phylogenetic signal in the temporal bone is largely related to similarities in size. Thus, with this study, we are not suggesting the use of a single 'character', such as size, for phylogenetic inference, but we do challenge the common view that shape, with its highly complex and multivariate nature, is necessarily more phylogenetically informative than size and that actually size and size-related shape variation (i.e., allometry) confound phylogenetic inference based on morphology. This perspective may in fact be less generalizable than often believed. Thus, while we confirm the original findings by Lockwood et al., we provide a deep reinterpretation of their nature and potential implications for hominid phylogenetics and we show how crucial it is not to overlook size in geometric morphometric analyses.

2015 - Why the Long Face? Kangaroos and Wallabies Follow the Same ‘Rule’ of Cranial Evolutionary Allometry (CREA) as Placentals [Articolo su rivista]
Cardini, Andrea Luigi; Polly, David; Dawson, Rebekah; Milne, Nick
abstract

Among closely related species, larger mammals tend to have a longer face and proportionally smaller braincase. This putative ‘rule’ in mammalian macroevolution has been proposed for the first time in 2013 based on 3D geometric morphometrics of antelopes, fruit bats, tree squirrels and mongooses. To firmly demonstrate that this trend holds as a ‘rule’ requires expanding the analysis in more lineages and other mammalian orders: if supported in most groups, it may indeed become a new evolutionary ‘rule’ besides famous ones such as Bergmann’s and Allen’s. In this study, using statistical shape analysis and both standard and comparative methods on a sample of kangaroos, wallabies and other macropodine marsupials, we show that the ‘big size-long face’ pattern is indeed found also outside the placentals. This provides support to the hypothesis of an important role of size-related shape changes (i.e., allometry) in the origin of the exceptional disparity of mammals, that, only in terms of size, span more orders of magnitude than any other animal: from 3 to 4 g of a tiny bat to more than 100 tons in blue whales.

2014 - Extreme climate, rather than population history, explains mid-facial morphology of Northern Asians [Articolo su rivista]
Evteev, A.; Cardini, Andrea Luigi; Morozova, I.; O’Higgins, P.
abstract

Previous studies have examined mid-facial cold adaptation among either widely dispersed and genetically very diverse groups of humans isolated for tens of thousands of years, or among very closely related groups spread over climatically different regions. Here we present a study of one East Asian and seven North Asian populations in which we examine the evidence for convergent adaptations of the mid-face to a very cold climate. Our findings indicate that mid-facial morphology is strongly associated with climatic variables that contrast the temperate climate of East Asians and the very cold and dry climate of North Asians. This is also the case when either maxillary or nasal cavity measurements are considered alone. The association remains significant when mtDNA distances among populations are taken into account. The morphological contrasts between populations are consistent with physiological predictions and prior studies of mid-facial cold adaptation in more temperate regions, but among North Asians there appear to be some previously undescribed morphological features that might be considered as adaptive to extreme cold. To investigate this further, analyses of the seven North Asian populations alone suggest that mid-facial morphology remains strongly associated with climate, particularly winter precipitation, contrasting coastal Arctic and continental climates. However, the residual covariation among North Asian mid-facial morphology and climate when genetic distances are considered, is not significant. These findings point to modern adaptations to extreme climate that might be relevant to our understanding of the mid-facial morphology of fossil hominins that lived during glaciations.

2014 - Just another island dwarf? Phenotypic distinctiveness in the poorly known Soemmerring's Gazelle,Nanger soemmerringii(Cetartiodactyla: Bovidae), of Dahlak Kebir Island [Articolo su rivista]
Chiozzi, Giorgio; Bardelli, Giorgio; Ricci, Marcella; De Marchi, Giuseppe; Cardini, Andrea Luigi
abstract

The gazelles of Dahlak Kebir are the only population of Nanger soemmerringii Cretzschmar, 1828 living on an island. Little is known on the biology of these animals, except that they are evidently smaller than their conspecifics living on the continent. We took advantage of a recently acquired collection of crania, probably the largest available study sample of the Dahlak Kebir population worldwide, to explore the phenotypic variation of this island endemism. To this aim, we employed state of the art geometric morphometrics techniques and multivariate statistics to compare the insular population with samples of two out of three subspecies of N. soemmerringii from continental Africa. We found that not only is the size of the animal remarkably smaller in Dahlak Kebir gazelles, but their cranial shape is also highly distinctive, and this might be only partly explained by allometry. We also showed that phenotypic variance might have been reduced in the island population, likely as a consequence of genetic bottlenecks. This unique population is part of a species vulnerable to extinction. Our results suggest that the Dahlak Kebir Island gazelles might represent a significant component of its variation and potential for adaptive change and evolution. More information, including molecular data, and an accurate assessment of its taxonomic relevance and conservation status, is urgently needed.

2014 - Missing the third dimension in geometric morphometrics: how to assess if 2D images really are a good proxy for 3D structures? [Articolo su rivista]
Cardini, Andrea
abstract

Procrustean geometric morphometrics has made large use of 2D images for studying three-dimensional structures such as mammalian bones or arthropod exoskeleta. This type of use of 2D data is still widespread today and will likely remain common for several years due to its simplicity, efficiency and low cost. However, using 2D pictures to measure morphological variation in a 3D object is an approximation that inevitably implies measurement error. Despite this being an obvious problem, which was emphasized since the early days of the first applications of geometric morphometrics to biology, whether 2D is a good proxy for 3D has been a rather neglected topic in the literature until very recently. In this paper, using marmot mandibles and crania as an example, I show how to assess the potentially crucial impact of 'missing the third dimension' in 2D landmarks and suggest a new method to test the accuracy of these data: the method is simple and can be easily performed in a user-friendly free software such as MorphoJ. This test is complimentary to other more exploratory analyses, that can also be performed using free programs and might offer a routine protocol to estimate the goodness of the 2D to 3D approximation in geometric morphometrics. Example data and a fully worked out MorphoJ project are provided for readers to learn how to replicate the analysis.

2014 - Morphometric analysis of pelvic sexual dimorphism in a contemporary Western Australian population [Articolo su rivista]
Franklin, Daniel; Cardini, Andrea Luigi; Flavel, Ambika; Marks, Murray K.
abstract

Requisite to routine casework involving unidentified skeletal remains is the formulation of an accurate biological profile, including sex estimation. Choice of method(s) is invariably related to preservation and by association, available bones. It is vital that the method applied affords statistical quantification of accuracy rates and predictive confidence so that evidentiary requirements for legal submission are satisfied. Achieving the latter necessitates the application of contemporary population-specific standards. This study examines skeletal pelvic dimorphism in contemporary Western Australian individuals to quantify the accuracy of using pelvic measurements to estimate sex and to formulate a series of morphometric standards. The sample comprises pelvic multi-slice computer tomography (MSCT) scans from 200 male and 200 female adults. Following 3D rendering, the 3D coordinates of 24 landmarks are acquired using OsiriX® (v.4.1.1) with 12 inter-landmark linear measurements and two angles acquired using MorphDb. Measurements are analysed using basic descriptive statistics and discriminant functions analyses employing jackknife validation of classification results. All except two linear measurements are dimorphic with sex differences explaining up to 65 % of sample variance. Transverse pelvic outlet and subpubic angle contribute most significantly to sex discrimination with accuracy rates between 100 % (complete pelvis-10 variables) and 81.2 % (ischial length). This study represents the initial forensic research into pelvic sexual dimorphism in a Western Australian population. Given these methods, we conclude that this highly dimorphic bone can be used to classify sex with a high degree of expected accuracy.

2013 - Biogeographic variation in the baboon: dissecting the cline [Articolo su rivista]
Dunn, Jason; Cardini, Andrea Luigi; Elton, Sarah
abstract

All species demonstrate intraspecific anatomical variation. While generalisations such as Bergman's and Allen's rules have attempted to explain the geographic structuring of variation with some success, recent work has demonstrated limited support for these in certain Old World monkeys. This study extends this research to the baboon: a species that is widely distributed across sub-Saharan Africa and exhibits clinal variation across an environmentally disparate range. This study uses trend surface analysis to map the pattern of skull variation in size and shape in order to visualise the main axes of morphological variation. Patterns of shape and size-controlled shape are compared to highlight morphological variation that is underpinned by allometry alone. Partial regression is used to dissociate the effects of environmental terms, such as rainfall, temperature and spatial position. The diminutive Kinda baboon is outlying in size, so analyses were carried out with and without this taxon. Skull size variation demonstrates an east-west pattern, with small animals at the two extremes and large animals in Central and Southern Africa. Shape variation demonstrates the same geographical pattern as skull size, with small-sized animals exhibiting classic paedomorphic morphology. However, an additional north-south axis of variation emerges. After controlling for skull size, the diminutive Kinda baboon is no longer an outlier for size and shape. Also, the east-west component is no longer evident and discriminant function analysis shows an increased misclassification of adjacent taxa previously differentiated by size. This demonstrates the east-west component of shape variation is underpinned by skull size, while the north-south axis is not. The latter axis is explicable in phylogenetic terms: baboons arose in Southern Africa and colonised East and West Africa to the north, diverging in the process, aided by climate-mediated isolating mechanisms. Environmental terms appear poorly correlated with shape variation compared with geography. This might indicate that there is no simple environment-morphology association, but certainly demonstrates that phylogenetic history is an overbearing factor in baboon morphological variation.

2013 - Clines in Africa: does size vary in the same way among widespread Sub-Saharan monkeys? [Articolo su rivista]
Cardini, Andrea Luigi; Dunn, J.; O'Higgins, P.; Elton, S.
abstract

Aim We characterize and compare patterns of clinal size variation amongdiverse widespread sub-Saharan monkeys with the aim of identifying common-alities and differences in biogeographical variation. Thus, we accurately quan-tify nonlinear clines in representatives of the main lineages of widespread sub-Saharan terrestrial and arboreal monkeys, and provide a crude numerical esti-mate of the strength of similarities across taxonomic groups.Location Sub-Saharan Africa.Methods Variations of skull centroid size, as a proxy for body mass, were modelledover sub-Saharan Africa within two terrestrial monkey species (Papio hamadryas andChlorocebus aethiops) and two arboreal monkey taxa (Procolobus (Piliocolobus) sp.,and the superspecies Cercopithecus nictitans – mitis) using inverse distance weighting,thin-plate splines and kriging. The model with the highest cross-validated accuracywas used to produce contour plots that visualized clines and predicted size at equallyspaced localities across overlapping areas of distribution ranges. Correlations amongthese predictions were used as a similarity measure among clines.Results Irrespective of phylogenetic distances and ecological differences, allgroups showed similarities in clinal size over central Africa: large animalsmostly live in and around the tropical forest of the Congo basin; size declinesrapidly towards the Horn of Africa and the coasts of Kenya and Tanzania. Sizealso tends to decrease in western Africa but clinal patterns in this region vary,with vervets exceptionally showing a size increase.Main conclusions Similarities in patterns of size across diverse monkey groupswere found. Nonetheless, complexity in clines and a degree of heterogeneity acrossgroups were evident, which is unlikely to be compatible with the exclusive effect onsize of a single main environmental factor. Primary productivity may be most sig-niﬁcant in relation to the consistent observation of large sizes in and adjacent tothe central African tropical forest belt. Complex clines, such as those of Africanmonkeys, are difﬁcult to compare visually and data collection from evenly sampledsets of localities, where all species of interest may be found, is often impractical orsimply not feasible for primates and other protected animals. The development ofimproved quantitative methods for the description and comparison of clines inmammals and other organisms is required.

2013 - Concordance of traditional osteometric and volume rendered MSCT interlandmark cranial measurements [Articolo su rivista]
Franklin, D.; Cardini, Andrea Luigi; Flavel, A.; Kuliukas, A.; Marks, M. K.; Hart, R.; Oxnard, C.; O’Higgins, P.
abstract

The statistical quantification of error and uncertainty is inherently intertwined with ascertaining the admissibility of forensic evidence in a court of law. In the forensic anthropological discipline, the robustness of any given standard should not only be evaluated according to its stated error, but the accuracy and precision of the raw data (measurements) from which they are derived. In the absence of Australian contemporary documented skeletal collections, medical scans (e.g. multislice computed tomography – MSCT) offer a source of contemporary population-specific data for the formulation of skeletal standards. As the acquisition of morphometric data from clinical MSCT scans is still relatively novel, the purpose of this study is to assess validity of the raw data that is being used to formulate Australian forensic standards.Six human crania were subjected to clinical MSCT at a slice thickness of 0.9mm. Each cranium and its corresponding volume rendered three-dimensional MSCT image were measured multiple times. Whether differences between MSCT and dry bone interlandmark measurements are negligible is statistically quantified; intra- and inter-observer measurement error is also assessed. We found that traditional bone measurements are more precise than their MSCT counterparts, although overall differences between the two data acquisition methods are negligible compared to sample variance. Cranial variation accounted on average for more than 20x the variance explained by MSCT vs. bone measurements. Similarly, although differences between operators were sometimes significant compared to intra-operator variance, they were negligible when compared to sample variance, which was on average 12x larger than that due to inter-operator differences.

2013 - Erratum to 'Estimation of sex from cranial measurements in a Western Australian population' [Forensic Sci. Int. 229 (2013) 158.e1-158.e8] [Articolo su rivista]
Franklin, D.; Cardini, A.; Flavel, A.; Kuliukas, A.
abstract

2013 - Estimation of sex from cranial measurements in a Western Australian population [Articolo su rivista]
Franklin, Daniel; Cardini, Andrea Luigi; Flavel, Ambika; Kuliukas, Algis
abstract

It is widely accepted that the most accurate statistical estimations of biological attributes in the human skeleton (e.g., sex, age and stature) are produced using population-specific standards. As we previously demonstrated that the application of foreign standards to Western Australian individuals results in an unacceptably large sex bias (females frequently misclassified), the need for population-specific standards is duly required and greatly overdue. We report here on the first morphometric cranial sexing standards formulated specifically for application in, and based on the statistical analysis of, contemporary Western Australian individuals. The primary aim is to investigate the nature of cranial sexual dimorphism in this population and outline a series of statistically robust standards suitable for estimating sex in the complete bone and/or associated diagnostic fragments. The sample analysed comprised multi-detector computed tomography cranial scans of 400 individuals equally distributed by sex. Following 3D volume rendering, 31 landmarks were acquired using OsiriX, from which a total of 18 linear inter-landmark measurements were calculated. Measurements were analysed using basic descriptive statistics and discriminant function analyses employing jackknife validations of classification results. All measurements (except frontal breadth and orbital height - Bonferroni corrected) are sexually dimorphic with sex differences explaining 3.5-48.9% of sample variance. Bizygomatic breadth and maximum length of the cranium and the cranial base contribute most significantly to sex discrimination; the maximum classification accuracy was 90%, with a -2.1% sex-bias. We conclude that the cranium is both highly dimorphic and a reliable bone for estimating sex in Western Australian individuals.

2013 - GEOMETRIC MORPHOMETRICS [Voce in Dizionario o Enciclopedia]
Cardini, Andrea Luigi
abstract

The aim of this article is to provide a simple introduction to Geometric MorphoMetrics (GMM). GMM is the numerical study of the interaction of size and shape with covarying factors in biology. It represents the modern form of morphometrics, a discipline with a century long history, and it includes a variety of methods. GMM makes extensive use of the advances in computer technology and digital imaging, providing tools to analyse and collect data within a rigorous statistical framework. Thanks to the combination of analytical power and intuitive visualizations using computer graphics, GMM has rapidly emerged as one of the most widely applied disciplines in biology. In this review, I will: 1) briefly summarize the history of morphometrics; 2) provide a rapid overview of the new methods; 3) describe and exemplify the analysis of anatomical landmark coordinates using Procrustes methods, the leading set of techniques in morphometrics. Specific topics, which may not be of interest for the general reader but could be of help to those who may want to learn and apply these methods, are discussed in a series of sections in the Appendix.

2013 - Larger mammals have longer faces because of size-related constraints on skull form [Articolo su rivista]
Cardini, Andrea Luigi; Polly, P. David
abstract

Facial length is one of the best known examples of heterochrony. Changes in the timing of facial growth have been invoked as a mechanism for the origin of our short human face from our long-faced extinct relatives. Such heterochronic changes arguably permit great evolutionary flexibility, allowing the mammalian face to be remodelled simply by modifying postnatal growth. Here we present new data that show that this mechanism is significantly constrained by adult size. Small mammals are more brachycephalic (short faced) than large ones, despite the putative independence between adult size and facial length. This pattern holds across four phenotypic lineages: antelopes, fruit bats, tree squirrels and mongooses. Despite the apparent flexibility of facial heterochrony, growth of the face is linked to absolute size and introduces what seems to be a loose but clade-wide mammalian constraint on head shape.

2013 - On growth and form in the "computer era": from geometric to biological morphometrics. [Articolo su rivista]
Cardini, Andrea Luigi; Loy, Anna
abstract

Almost 100 years after the publication of Thompson's seminal book "On growth and form", the study of animal morphology is becoming again central to biology. This is also thanks to the development of powerful computerized quantitative methods for statistical shape analysis, collectively known as geometric morphometrics (GM). GM was announced as a revolution just two decades ago. The "revolution" is now a standard tool in numerical analyses of phenotypic variation in mammals and other organisms. Hundreds of studies are published every year that take advantage of GM (e.g., more than 800 entries in Google Scholar only for 2012). We celebrate the 20t anniversary of the "revolution in morphometrics" (Rohlf and Marcus, 1993, p. 129) with the publication of a "Yellow Book", a special issue of Hystrix dedicated to Evolutionary Morphometrics and Virtual Morphology. A series of 14 papers by leading morphometricians summarizes the main achievements in GM (surface methods, comparative shape analysis, phenotypic trajectories quantification, modularity/integration, the use of R in morphometrics), describes its most innovative developments (ecometrics, eigensound analysis, biomechanical GM), and discusses common misunderstandings of well extablished methods (visualization of shape differences). Besides celebrating the success of statistical shape analysis in biology, this issue aims at introducing to GM readers unfamiliar with or intimidated by its strong numerical background. This is why, as Editors, we asked all contributors to provide concise and accurate but also clear and simple descriptions of techniques and applications. We hope that we succeeded in this aim, and wish that this Yellow Book may help to tighten the connection between biologists and statisticians for a truly "biological" GM.

2013 - Rings without a lord? Enigmatic fossils from the lower Palaeozoic of Bohemia and the Carnic Alps [Articolo su rivista]
Ferretti, Annalisa; Cardini, Andrea Luigi; Crampton, James S.; Serpagli, Enrico; David Sheets, H.; Štorch, Petr
abstract

Fossilized ring-like structures, whose function and taxonomic affiliation are enigmatic, were recovered for the first time from the Upper Ordovician of the Carnic Alps and the Silurian of Bohemia. These rings, already mentioned as minor constituents in previous conodont studies (e.g., Webers 1966; Bischoff 1973), were reported from the Palaeozoic of several regions in Europe and North America. Originally considered as inwardly accreted adhering discs of a benthic Hyolithelminth worm with a phosphatic tubular projection, they were later reinterpreted in relation to a putative crinoid epibiont or even as possible Scyphozoans. Despite a long debate, neither the function of the enigmatic Palaeozoic rings nor their taxonomic affiliation have been fully clarified.The study material, extracted with a standard technique in use for conodonts, consists of 235 elements from 16 stratigraphic levels in the Plöcken Formation (Carnic Alps, Cellon Section; Amorphognathus ordovicicus Biozone, Hirnantian, Ordovician) and in the Kopanina Formation (Bohemia, Mušlovka Quarry; Polygnathoides siluricus Biozone, Ludfordian, Silurian). To explore whether ring size and shape changed over time, we employed a novel combination of geometric morphometric approaches for outlines with no 'homologous' landmarks and showed that only size appreciably varied with an increase of ca. 20%.The emerging data from this study are consistent with the interpretation of the rings as an adhering structure of a benthic organism living on a relatively uniform hard substrate.

2013 - The long and winding road: identifying pig domestication through molar size and shape [Articolo su rivista]
A., Evin; T., Cucchi; Cardini, Andrea Luigi; U. S., Vidarsdottir; G., Larson; K., Dobney
abstract

The ability to document the effects of domestication from archaeological remains of animals and plants is essential for reconstructing the history of one of the most important transitions in human prehistory – the shift from hunting and gathering to farming. In mammals, teeth are well preserved in archaeological remains and are known to be taxonomically informative. In this study, we compare three sets of dental morphometric descriptors in wild and domestic pigs {(Sus} scrofa) – maximum length, size and shape variables from {2D} geometric morphometrics – in order to assess which of the three provides the best ability to correctly distinguish current wild and domestic West Palaearctic pigs. For this purpose, we used predictive linear discriminant analysis with cross-validation taking into account potential bias due to heterogeneous sample sizes and important number of predictors. Classification accuracy of wild and domestic status ranged between 77.3 and 93\% depending of the tooth and the descriptor analyzed. However, individual posterior probabilities of correct classification were appreciably smaller when using tooth length and centroid size compared to shape variables. Size appeared to be a poor indicator of wild and domestic status, contrary to shape which in addition provides a high degree of confidence in the wild versus domestic predictions. Our results indicate that geometric morphometrics offers an extremely powerful alternative to more traditional biometric approaches of length and width measurements to capture the elusive morphological changes induced by the domestication process in archaeological remains.

2013 - Virtual Morphology and Evolutionary Morphometrics in the new millenium. [Monografia/Trattato scientifico]
Cardini, Andrea Luigi; Loy, Anna
abstract

EDITED VOLUME; abstract N/A

2012 - Can morphospace shed light on cave bear spatial-temporal variation? Population dynamics of Ursus spelaeus from Romualdova pećina and Vindija, (Croatia) [Articolo su rivista]
T. K., Seetah; Cardini, Andrea Luigi; P. T., Miracle
abstract

Cave bear (Ursus spelaeus) behavioural ecology, as evidenced through population dynamics, is crucial forimproving our understanding of why this species went extinct. Despite the fact that the bones of thisspecies have been recovered in very large quantities, allowing for extensive study, fundamental questionsregarding its life-ways remain unanswered. We present research using geometric morphometrics (GMM)on molars to investigate population structure based on morphological variation over space and throughtime. This preliminary work deliberately restricts the geographic catchment area for sampling, allowingfor a meaningful appraisal of scale of variation within a spatially conservative framework. Our resultsdemonstrate no signiﬁcant morphological variation evident temporally and a small but statisticallysigniﬁcant degree of shape variation geographically despite the proximity of the study localities. Theseﬁndings suggest that an accurate quantitative exploration of morphospace may be an important source ofevidence on environmental and climatic shifts and the resulting inﬂuence on animal morphology.

2012 - Estimation of sex from sternal measurements in a Western Australian population [Articolo su rivista]
Daniel, Franklin; Ambika, Flavel; Algis, Kuliukas; CARDINI, Andrea Luigi; Murray, K. Marks; Charles, Oxnard; Paul, O’Higgins
abstract

In Australia, particularly Western Australia, there is a relative paucity of contemporary population-specific morphometric standards for the estimation of sex from unknown skeletal remains. This is largely a historical artefact from lacking, or poorly documented, repositories of human skeletons available for study. However, medical scans, e.g. MSCT (multislice spiral computed tomography) are an ingenious and practical alternative source for contemporary data. To that end, this study is a comprehensive analysis of sternal sexual dimorphism in a sample of modern Western Australian (WA) individuals with a main purpose to develop a series of statistically robust standards for the estimation of sex. The sample comprises thoracic MSCT scans, with a mean of 0.9 millimeter (mm) slice thickness, on 187 non-pathological sterna. Following 3D volume rendering, 10 anatomical landmarks were acquired using OsiriX® (version 3.9) and a total of 8 inter landmark linear measurements were calculated using Morph Db (an in-house developed database application). Measurements were analyzed using basic descriptive statistics and discriminant function analyses, with statistical analyses performed using SPSS 19.0. All measurements are sexually dimorphic and sex differences explain 9.8–47.4% of sample variance. The combined length of the manubrium and body, sternal body length, manubrium width, and corpus sterni width at first sternebra contribute significantly to sex discrimination and yield the smallest sex-biases. Cross-validated classification accuracies, i.e., univariate, stepwise and direct function, are 72.2–84.5%, with a sex bias of less than 5%. We conclude that the sternum is a reliable element for sex estimation among Western Australians.

2012 - Less is more: researcher survival guide in times of economic crisis. [Articolo su rivista]
Cagnacci, F.; Cardini, Andrea Luigi; Ciucci, P.; Ferrari, N.; Mortelliti, A.; Preatoni, D.; Russo, D.; Scandura, M.; Wauters, L.; Amori, G.
abstract

The global economic crisis leads to important changes in investment policies that hit scientific research too. Scientists are currently facing a period of limited availability of research funds. However, this period of shortage of economic resources may also represent an opportunity of re- newal for scientific research, since it may call for improved efficiency and effectiveness and lead to a critical re-evaluation of strategies and priorit- ies. In this opinion paper, we collated a scattered and non-exhaustive list of suggestions for mammal research during a period of limiting financial resources. Our main objective is to stimulate debate, and possibly provide some useful hints, especially to young mammalogists.

2012 - Rings without a lord? Enigmatic fossils from the Lower Paleozoic of Bohemia and the Carnic Alps. [Abstract in Atti di Convegno]
Ferretti, Annalisa; Cardini, Andrea Luigi; Crampton, James S.; Rigoni, Cecilia; Serpagli, Enrico; Sheets, H. David; Štorch, Peter
abstract

2012 - The application of traditional and geometric morphometric analyses for forensic quantification of sexual dimorphism: preliminary investigations in a Western Australian population [Articolo su rivista]
D., Franklin; Cardini, Andrea Luigi; A., Flavel; A., Kuliukas
abstract

A current limitation of forensic practice in Western Australia is a lack of contemporary population-specific standards for biological profiling; this directly relates to the unavailability of documented human skeletal collections. With rapidly advancing technology, however, it is now possible to acquire accurate skeletal measurements from {3D} scans contained in medical databases. The purpose of the present study, therefore, is to explore the accuracy of using cranial form to predict sex in adult Australians. Both traditional and geometric morphometric methods are applied to data derived from {3D} landmarks acquired in {CT-reconstructed} crania. The sample comprises multi-detector computed tomography scans of 200 adult individuals; following {3D} volume rendering, 46 anatomical landmarks are acquired using {OsiriX} (version 3.9). Centroid size and shape (first 20 {PCs} of the Procrustes coordinates) and the inter-landmark {(ILD)} distances between all possible pairs of landmarks are then calculated. Sex classification effectiveness of the {3D} multivariate descriptors of size and shape and selected {ILD} measurements are assessed and compared; robustness of findings is explored using resampling statistics. Cranial shape and size and the {ILD} measurements are sexually dimorphic and explain 3.2 to 54.3 \% of sample variance; sex classification accuracy is 83.5–88.0 \%. Sex estimation using {3D} shape appears to have some advantages compared to approaches using size measurements. We have, however, identified a simple and biologically meaningful single non-traditional linear measurement (glabella–zygion) that classifies Western Australian individuals according to sex with a high degree of expected accuracy (87.5–88 \%).

2011 - Discriminant function analyses in archaeology: are classification rates too good to be true? [Articolo su rivista]
K., Kovarovic; L. C., Aiello; Cardini, Andrea Luigi; C. A., Lockwood
abstract

The use of discriminant function analyses (DFA) in archaeological and related research is on the increase, however many of the assumptions of this method receive a mixed treatment in the literature. Statisticians frequently use complex statistical models to investigate analytical parameters, but such idealised datasets may be hard to relate to "real-life" examples and the literature difficult to assess. Using two faunal datasets that are more typical of archaeological and related research, one comprised of size-corrected linear measurements of bovid humeri and another of 3D geometric morphometric (GMM) shape data of African monkey skulls, and two simulated datasets, we illustrate some of the most important but often ignored issues of DFA. We specifically show why it is paramount to address "over-fitting" by cross-validation when applying this method and how the probability of correctly classifying cases by chance can be properly and explicitly taken into account. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.

2011 - Exploring Clinal Variation in the Morphology of Baboons (Papio spp.): A Geometric Morphometric Approach [Abstract in Rivista]
J., Dunn; Cardini, Andrea Luigi; S., Elton
abstract

2011 - GeMBiD, a Geometric Morphometric Approach to the Study of Biological Diversity: An Example Study of the Red Colobus (Procolobus Piliocolobus ) Species Complex [Articolo su rivista]
Cardini, Andrea Luigi; S., Elton
abstract

Determining conservation priorities requires an understanding of biological diversity in terms of both genetic variation and phenotypic difference. The phenotype is where many adaptations are expressed and thus provides the potential for future evolution, including responses to rapidly changing environments. We suggest that applying geometric morphometrics (a set of methods related to image analysis) to the study of morphological differences among closely related populations can effectively quantify phenotypic variation in poorly studied taxa, and provide an informative estimate of the degree of morphological divergence relative to their better known relatives. The approach is simple and flexible, but has proven to be powerful. As an example of a Geometric Morphometric approach to the study of Biological Diversity (GeMBiD), we provide a preliminary estimate of the morphological distinctiveness of a poorly studied red colobus monkey, the Semliki red colobus (Procolobus sp. ellioti), by using cross-validated discriminant analyses on cranial shape data and comparing chance-corrected classification accuracy in this population with that of other populations of monkeys within and outside the red colobus lineage. By fruitfully exploiting available museum collections and by developing networks of scientists who can provide information on and study material from rare populations, GeMBiD could become a useful tool for complementing genetic analyses of biodiversity.

2011 - Leaf Morphology, Taxonomy and Geometric Morphometrics: A Simplified Protocol for Beginners [Articolo su rivista]
V., Viscosi; Cardini, Andrea Luigi
abstract

Taxonomy relies greatly on morphology to discriminate groups. Computerized geometric morphometric methods for quantitative shape analysis measure, test and visualize differences in form in a highly effective, reproducible, accurate and statistically powerful way. Plant leaves are commonly used in taxonomic analyses and are particularly suitable to landmark based geometric morphometrics. However, botanists do not yet seem to have taken advantage of this set of methods in their studies as much as zoologists have done. Using free software and an example dataset from two geographical populations of sessile oak leaves, we describe in detailed but simple terms how to: a) compute size and shape variables using Procrustes methods; b) test measurement error and the main levels of variation (population and trees) using a hierachical design; c) estimate the accuracy of group discrimination; d) repeat this estimate after controlling for the effect of size differences on shape (i.e., allometry). Measurement error was completely negligible; individual variation in leaf morphology was large and differences between trees were generally bigger than within trees; differences between the two geographic populations were small in both size and shape; despite a weak allometric trend, controlling for the effect of size on shape slighly increased discrimination accuracy. Procrustes based methods for the analysis of landmarks were highly efficient in measuring the hierarchical structure of differences in leaves and in revealing very small-scale variation. In taxonomy and many other fields of botany and biology, the application of geometric morphometrics contributes to increase scientific rigour in the description of important aspects of the phenotypic dimension of biodiversity. Easy to follow but detailed step by step example studies can promote a more extensive use of these numerical methods, as they provide an introduction to the discipline which, for many biologists, is less intimidating than the often inaccessible specialistic literature.

2011 - Morphometrics and phylogenetics: Principal components of shape from cranial modules are neither appropriate nor effective cladistic characters [Articolo su rivista]
D. C., Adams; CARDINI, Andrea Luigi; L. R., Monteiro; P., O'Higgins; F. J., Rohlf
abstract

Not available

2010 - A Geometric Morphometric Approach to the Quantification of Population Variation in Sub-Saharan African Crania [Articolo su rivista]
D., Franklin; Cardini, Andrea Luigi; C. E., Oxnard
abstract

We report here on new data examining cranial variation in 18 modern human sub-Saharan African populations. Previously, we investigated variation within southern Africa; we now extend our analyses to include a series of Central, East, and West African crania, to further knowledge of the relationships between, and variation and regional morphological patterning in, those populations. The sample comprises 377 male individuals; the three-dimensional coordinates of 96 landmarks are analyzed using Procrustes-based methods. Interpopulation variation is examined by calculating shape distances between groups, which are compared using resampling statistics and parametric tests. Phenotypic variance, as a proxy for genetic variance, is measured and compared across populations. Principal components and cluster analyses are employed to explore relationships between the populations. Shape differences are visualized using three-dimensional rendered models. Observed disparity patterns imply a mix of differences and similarities across populations, with no apparent support for genetic bottlenecks, which is likely a consequence of migrations that may have influenced differences in cranial form; supporting data are found in recent molecular studies. The Pygmy sample had the most distinctive cranial morphology; characteristically small in size with marked prognathism. These features characterized, although less strongly, the neighboring Bateke, and are possibly related to similar selective pressures in conjunction with interbreeding. Small cranial size is also involved in the considerable distinctiveness of the San and Khoikhoi. The statistical procedures applied in this study afford a powerful and robust means of quantifying and visualizing the magnitude and pattern of cranial variation between sub-Saharan African populations. Am. J. Hum. Biol. 22:23-35, 2010. (C) 2009 Wiley-Liss, Inc.

2010 - A geometric morphometric assessment of the optic cup in glaucoma [Articolo su rivista]
P. G., Sanfilippo; Cardini, Andrea Luigi; I. A., Sigal; J. B., Ruddle; B. E., Chua; A. W., Hewitt; D. A., Mackey
abstract

The morphologic appearance of the optic disc is of interest in glaucoma. In contrast to descriptive classification systems that are currently used, a quantitative approach to the analysis of optic disc morphology is required. Our goal was to determine the optimal method for quantifying optic cup shape by comparing traditional (ovality, form-factor and neuroretinal rim (NRR) width ratio) and geometric morphometric approaches. Left optic disc stereophotographs of 160 (80 normal and 80 glaucomatous (stratified by severity)) subjects were examined. The optic cup margins were stereoscopically delineated with a custom tracing system and saved as a series of discrete points. The geometric morphometric methods of elliptic Fourier analysis (EFA) and sliding semi-landmark analysis (SSLA) were used to eliminate variation unrelated to shape (e.g. size) and yield a series of shape variables. Differences in optic cup shape between normal and glaucoma groups were investigated. Discriminant functions were computed and the sensitivity and specificity of each technique determined. Receiver operator characteristic (ROC) curves were calculated for all methods and evaluated in their potential to discriminate between normal and glaucomatous eyes based on the shape variables. All geometric morphometric methods revealed differences between normal and glaucomatous eyes in optic cup shape, in addition to the traditional parameters of ovality, form-factor and NRR width ratio (p<0.0005). SSLA (minimum bending energy criterion - 18 points) had the best sensitivity (83%) and area under the curve (AUC) (0.91). EFA (72 points) performed similarly well (74%, 0.89) as did the set of traditional shape-based variables (76%, 0.86). This study demonstrated that a geometric morphometric approach for discriminating between normal and glaucomatous eyes in optic cup shape is superior to that provided by traditional single parameter shape measures. Such analytical techniques could be incorporated into future automated optic disc screening modalities. (C) 2010 Elsevier Ltd. All rights reserved.

2010 - Biogeographic Analysis Using Geometric Morphometrics: Clines in Skull Size and Shape in aWidespread African Arboreal Monkey [Capitolo/Saggio]
Cardini, Andrea Luigi; José Alexandre Felizola Diniz, Filho; P., David Polly; Sarah, Elton
abstract

Despite the “renaissance” of biogeography in the last two decades with its centralrole in the study of biodiversity and evolution, and the “revolution” in morphometricsbrought about by methods based on the analysis of Cartesian coordinates ofanatomical landmarks, the use of geometric morphometrics in biogeographic studieshas been rather limited. With this analysis we aim to provide an example ofhow geometric morphometrics can fruitfully be applied to the study of clinal variationin a widespread African monkey group by a simple extension of methodswidely employed by macroecologists and biogeographers to multivariate shape data.Throughout the paper we aim to explain these techniques so that those who are newto them can use and adapt them for their own needs, in some cases providing specificinstructions on how to perform certain operations in standard morphometricsand statistical software. Our hope is that this may stimulate morphometricians andscientists from other disciplines to explore geographic variation in size and shapeusing up-to-date geometric morphometric methods. The application of geometricmorphometrics to ecological, biogeographic and phylogeographic studies has enormouspotential for a thorough understanding of how form changes in space and timeduring evolution and in relation to genetic and environmental factors.

2010 - Size variation facilitates population divergence but does not explain it all: an example study from a widespread African monkey [Articolo su rivista]
S., Elton; J., Dunn; Cardini, Andrea Luigi
abstract

Subspecific variation is widespread in vertebrates. Within Africa, several mammals have extensive geographic distributions with attendant morphological, ecological, and behavioural variations, which are often used to demarcate subspecies. In the present study, we use a primate species, the vervet monkey, Cercopithecus aethiops, as a case study for intraspecific divergence in widespread mammals, assessed through hard tissue morphology. We examine intraspecific differences in size, shape, and non-allometric shape from a taxonomic perspective, and discuss the macroevolutionary implications of findings from microevolutionary analyses of geographic variation. A geometric morphometric approach was used, employing 86 three-dimensional landmarks of almost 300 provenanced crania. Many of the taxonomic differences in skull morphology between vervet populations appear to be related to geographic proximity, with subspecies at opposite extremes of a west-to-east axis showing greatest divergence, and populations from central and south Africa being somewhat intermediate. The classification rate from discriminant analyses was lower than that observed in other African primate radiations, including guenons as a whole and red colobus. Nonetheless, taxonomic differences in shape were significant and not simply related to either geography or size. Thus, although shifts in size may be an important first step in adaptation and diversification, with size responding more quickly than shape to environmental change, the six vervet taxa currently recognized (either as species or subspecies) are not simply allometrically scaled versions of one another and are probably best viewed as subspecies. Holding allometry constant when examining inter-population differences in shape may thus help to reveal the early stages of evolutionary divergence. The vervet case study presented here hence has relevance for future studies examining intraspecific differentiation in other large mammals, particularly through the methods used to identify small but biologically meaningful divergence, with attendant implications for conservation planning. (C) 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101, 823-843.

2009 - Detecting biological uniqueness using geometric morphometrics: an example case from the Vancouver Island marmot [Articolo su rivista]
Cardini, Andrea Luigi; D:, Nagorsen; P., O’Higgins; P. D., Polly; Jr R. W., Thorington; P., Tongiorgi
abstract

The Vancouver Island marmot (M. vancouverensis) consists of a small insular population with an uncommon dark-brown pelage colour. This population provides an excellent example of how morphology and molecules can tell very different stories about the evolution of a group. Mitochondrial DNA indicates that the degree of divergence of M. vancouverensis is minimal and actually comparable or even smaller than among populations of continental species of marmots. Accurate geometric morphometric analyses on crania and mandibles from modern and subfossil samples, in contrast, convincingly demonstrate that the Vancouver Island marmot is one of the most distinctive populations among all living marmots. Thus, M. vancouverensis is not simply a dark variant of its sister species M. caligata but represents a highly morphologically derived population whose evolutionary significance is overlooked by molecular analyses. In this study, we show how geometric morphometrics can complement studies of genetic divergence by measuring the phenotypic dis- tinctiveness of a population. This was done by performing cross-validated discriminant analyses on mandibular shape in the Vancouver Island marmot and its closest Nearctic relatives. Thus, we found that using mandibles we can achieve in M. vancouverensis a classification accuracy as high as for ‘good species’ (i.e., species which are also significantly divergent in molecular analyses) and much higher than in populations within those same species. The approach used in this study is simple, effective and, at least in this specific case, fairly robust to sampling error in small samples. Thus, such morphological analysis seems promising as a tool complementary to molecular studies to aid detection of biological distinctiveness in natural populations. We suggest that its potential should be explored and its usefulness examined also in Palearctic marmots and other mammals. If successful, the ‘geometric morphometric approach to the study of biological diversity‘ would add a phenotypic dimension to the characterization of the evolutionary significance of populations. In turn, this would allow a more inclusive understanding of the complexity of adaptive variation with potential implications for conservation biology.

2009 - Geographical and taxonomic influences on cranial variation in red colobus monkeys (Primates, Colobinae): introducing a new approach to 'morph' monkeys [Articolo su rivista]
Cardini, Andrea Luigi; S., Elton
abstract

To provide accurate but parsimonious quantitative descriptions of clines in cranial form of red colobus, to partition morphological variance into geographical, taxonomic and structured taxonomic components, and to visually summarize clines in multivariate shape data using a method which produces results directly comparable to both univariate studies of geographical variation and standard geometric morphometric visualization of shape differences along vectors. Equatorial Africa. Sixty-four three-dimensional cranial landmarks were measured on 276 adult red colobus monkeys sampled over their entire distribution. Geometric morphometric methods were applied, and size and shape variables regressed onto geographical coordinates using linear and curvilinear models. Model selection was done using the second-order Akaike information criterion. Components of variation related to geography, taxon or their combined effect were partitioned using partial regresssion. Multivariate trends in clinal shape were summarized using principal components of predictions from regressions, plotting vector scores on maps as for univariate size, and visualizing differences along main axes of clinal shape variation using surface rendering. Significant clinal variation was found in size and shape. Clines were similar in females and males. Trend surface analysis tended to be more accurate and parsimonious than alternative models in predicting morphology based on geography. Cranial form was relatively paedomorphic in East Africa and peramorphic in central Africa. Most taxonomic variation was geographically structured. However, taxonomic differences alone accounted for a larger proportion of total explained variance in shape (up to 40%) than in size (<= 20%). A strong cline explained most of the observed size variation and a significant part of the shape differences of red colobus crania. The pattern of geographical variation was largely similar to that previously reported in vervets, despite different habitat preferences (arboreal versus terrestrial) and a long period since divergence (c. 14-15 Myr). This suggests that some aspects of morphological divergence in both groups may have been influenced by similar environmental, geographical and historical factors. Cranial size is likely to be evolutionarily more labile and thus better reflects the influence of recent environmental changes. Cranial shape could be more resilient to change and thus better reflects phylogenetically informative differences.

2009 - Monkey macroecology: spatial, environmental and taxonomic influences on cranial morphology in Piliocolobus and Chlorocebus [Abstract in Rivista]
S., Elton; Cardini, Andrea Luigi
abstract

abstract

2009 - Optic disc morphology - Rethinking shape [Articolo su rivista]
P. G., Sanfilippo; Cardini, Andrea Luigi; A. W., Hewitt; J. G., Crowston; D. A., Mackey
abstract

Morphometrics, a branch of morphology, represents the study of size and shape components of biological form and their variation in the population. Assessment of optic disc morphology is essential in the diagnosis and management of many ophthalmic disorders. Much work has been performed to characterize size-related parameters of the optic disc; however, limited information is available on shape variation in the general population. In contrast to optic disc or cup sizes, which are conceptually meaningful variables with a defined unit of measurement, there are few metric constructs by which to quantify, visualize and interpret variation in optic disc or cup shape. This has significance in ophthalmic diseases with a genetic basis as recent evidence has suggested that optic disc shape may be heritable. Conventional optic disc shape measures of 'ovality' and 'form-factor' reduce a complex structure to a single number and eliminate information of potential diagnostic relevance from further analyses. The recent advent of 'geometric morphometrics', a branch of statistics that incorporates tools from geometry, biometrics and computer graphics in the quantitative analysis of biological forms, has enabled spatial relationships in shape data to be retained during analysis. The analytical methods employed in geometric morphometrics can be separated into two distinct groups: landmark-based (e.g. Procrustes analysis, thin-plate splines) and boundary outline techniques (e.g. Fourier analysis). In this review, we summarize current approaches to the study of optic disc morphology, discuss the underlying theory of geometric morphometrics within the context of analytical techniques and then explore the contemporary relevance of the subject matter to several biological fields. Finally we illustrate the potential application of geometric morphometrics to the specific problem of optic disc shape and glaucoma assessment. (C) 2009 Elsevier Ltd. All rights reserved.

2009 - Tempo and mode of evolutionary divergence in modern and Holocene Vancouver Island marmots (Marmota vancouverensis) (Mammalia, Rodentia) [Articolo su rivista]
D. W., Nagorsen; Cardini, Andrea Luigi
abstract

Marmota vancouverensis is the only insular species among the 14 species of marmots. The evolutionary history of this species is unresolved. Although M. vancouverensis is strongly differentiated in osteological and other morphological characters, its low genetic divergence suggests recent evolution from an ancestral continental species. We used geometric morphometric techniques to assess the morphology of hemimandibles from 239 modern M. vancouverensis, Marmota caligata, Marmota flaviventris, Marmota olympus and 30 Holocene (9435-735 cal. yr bp) subfossil M. vancouverensis. Our results confirm that the mandible of M. vancouverensis is strongly differentiated in shape from continental marmot species, but similar in size to its mainland sister species M. caligata. Temporal variation in size and shape over the past 2500 years among allochronic samples of M. vancouverensis was minimal suggesting that the morphological divergence of this species occurred in a period of rapid change following its isolation from mainland populations in the late Pleistocene. Selection pressures associated with environmental changes and founder effects and genetic drift resulting from population bottlenecks created by population declines and habitat fragmentation are hypothesized as factors contributing to the morphological divergence of this species.

2009 - The phylogenetic signal in cranial morphology of Vipera aspis: a contribution from geometric morphometrics [Articolo su rivista]
Gentilli, A.; Cardini, Andrea Luigi; Fontaneto, D.; Zuffi, M. A. L.
abstract

Morphological variation in the frontal bone and cranial base of Vipera aspis was studied using geometric morphometrics. Significant differences in shape were found among samples from subspecies present in Italy (V. a. aspis, V. a. francisciredi, V. a. hugyi). Sexual dimorphism was negligible as well as allometry and size differences. The most divergent subspecies was V. a. aspis, possibly in relation to its recent history of geographic isolation in a glacial refugium. Shape clusters were in good agreement with clusters from studies of external morphology and completely congruent with results from molecular studies of mtDNA.

2009 - The radiation of red colobus monkeys (Primates, Colobinae): morphological evolution in a clade of endangered African primates [Articolo su rivista]
Cardini, Andrea Luigi; S., Elton
abstract

Red colobus monkeys are a group of African monkeys that include some of the most endangered primate populations. Despite urgently needing to understand the importance of particular populations for preserving the biodiversity of this lineage, their evolutionary relationships remain poorly understood, and their taxonomy is unstable, and often enigmatic. Data on behaviour, ecology, genetics, and morphology are thus strongly needed to address taxonomic issues that are not only relevant for primatologists, but also for conservation biologists. In this study, we investigated the morphological diversity and evolution of red colobus by examining the cranial variation of 369 individuals from most living populations. Crania were measured using a set of 64 anatomical landmarks, and were analysed using geometric morphometric methods for the study of three-dimensional landmark coordinates. We found significant differences among most of the populations traditionally described on the basis of pelage colour and geographic distribution. However, differences tended to be smaller within biogeographic assemblages, which might be related to mountain refugia during periods of forest contraction in the Pleistocene.We also found a tendency towards large taxonomic distances, which suggested that populations might have originated earlier than has been traditionally thought, a result congruent with a recent molecular phylogenetic analysis. However, the distinctive forms of East African relict populations might be related to an acceleration of morphological evolution in small peripheral isolates, under strong selective pressures. This indicates that small and isolated populations, which are also the most endangered ones, might indeed be unique representatives of the red colobus radiation, and hence contribute to its biodiversity significantly. However, in- depth morphological studies of red colobus, particularly those in peripheral populations that tend to be rare in the wild, as well as in museum collections, is hampered by a paucity of data. In these cases, populations might be extinct before primatologists and conservationsts can even appreciate what was lost. (C) 2009 The Linnean Society of London, Zoological Journal of the Linnean Society, 2009.

2008 - Anthropology from the desk? The challenges of the emerging era of data sharing [Articolo su rivista]
S., Elton; Cardini, Andrea Luigi
abstract

Not available

2008 - Does the skull carry a phylogenetic signal? Evolution and modularity in the guenons [Articolo su rivista]
CARDINI, Andrea Luigi; S., Elton
abstract

Form and genes often tell different stories about the evolution of animals, with molecular data generally considered to be more objective than morphological data. However, form provides the basis for the description of organisms, and the study of fossils crucially depends on morphology. Complex organisms tend to evolve as 'mosaics', in which parts may be modified at varying rates and in response to different selective pressures. Thus, individual anatomical regions may contain different phylogenetic signals. In the present study, we used computerized methods to 'dissect' the skulls of a primate clade, the guenons, into functional and developmental modules (FDM). The potential of different modules as proxies for phylogenetic divergence in modern lineages was investigated. We found that the chondrocranium was the only FDM in which shape consistently had a strong and significant phylogenetic signal. This region might be less susceptible to epigenetic factors and thus more informative about phylogeny. The examination of the topology of trees from the chondrocranium suggested that the main differences evolved at the time of the radiation of terrestrial and arboreal guenons. However, phylogenetic reconstructions were found to be strongly affected by sampling error, with more localized anatomical regions (i.e. smaller/less complex FDMs) generally producing less reproducible tree topologies. This finding, if confirmed in other groups, implies that the utility of specific FDMs for phylogenetic inference could, in many cases, be hampered by the low reproducibility of results. The study also suggested that uncertainties due to sampling error may be larger than those from character sampling. This might have implications for phylogenetic analyses, which typically provide estimates of support of tree nodes based on characters but do not generally take into account the effect of sampling error on the tree topology. Nonetheless, studies of the potential of different FDMs as proxies for phylogenetic divergence in modern lineages, such as the present study, provide a framework that may help in modelling the morphological evolution of present and fossil species. (C) 2008 The Linnean Society of London.

2008 - Evolutionary Acceleration and Divergence in Procolobus kirkii [Articolo su rivista]
K., Nowak; Cardini, Andrea Luigi; S., Elton
abstract

We investigated the role of geographical insularity in divergence and speciation of Procolobus kirkii by examining cranial morphology. The sample (n=369) included museum specimens of Procolobus spp. and recently deceased individuals of P. kirkii from the main island of Zanzibar and 2 smaller islands in the archipelago. Geometric morphometrics evinced pronounced divergence of Procolobus kirkii from mainland Procolobus, including members of P. badius ssp., P. pennantii ssp., P. rufomitratus, P. gordonorum and also representatives of the assemblage of red colobus populations from Central Equatorial Africa. Procolobus kirkii has a small cranium, consistent with the island rule for large mammals, reduced sexual dimorphism consistent with Rensch's rule, and a distinct cranial form. Analyses of phenotypic variance of Procolobus kirkii gave no evidence for population bottlenecks in the history of the species, but there is a clear indication that the species has experienced accelerated morphological evolution of size, probably as a result of insularity. Their highly distinctive morphology lends weight to the argument that they are a unique insular endemic species in need of active conservation.

2008 - Evolutionary acceleration and divergence in Procolobus kirkii (International Journal of Primatology DOI: 10.1007/s10764-008-9306-1) [Articolo su rivista]
Nowak, K.; Cardini, A.; Elton, S.
abstract

2008 - GeMBiD, a ‘Geometric morphometric approach to the study of biological diversity’ [Altro]
Cardini, Andrea Luigi; Elton, S.
abstract

2008 - Mandibular morphology as an indicator of human subadult age: geometric morphometric approaches [Articolo su rivista]
D., Franklin; Cardini, Andrea Luigi; P., O'Higgins; C. E., Oxnard; I., Dadour
abstract

Methods for skeletal identification have a long history in physical and forensic anthropology. Recent literature demonstrates that new methods are constantly being developed, concurrent with refinements to those already commonly employed. The present study concerns the application of geometric morphometrics to assess the potential of mandibular morphology as a developmental marker for estimating age at death in subadult human skeletal remains. The sample comprises 79 known age and sex subadult individuals of South African Bantu and African American origin; 38 bilateral three-dimensional landmarks were designed and acquired using a portable digitizer. Linear regression was used to predict age using the multivariate descriptors of mandible size and shape based on configurations of three-dimensional landmarks. Our results show that the mandible can be used to predict age in the subadult skeleton with accuracy comparable to standards based on the dentition (standard error rates are between +/- 13 and +/- 3.0 years). These results closely parallel our previous study using the linear measurement of ramus height, but suggest that geometric morphometrics may be slightly more accurate when adolescents are included in the sample.

2008 - Variation in guenon skulls (I): species divergence, ecological and genetic differences [Articolo su rivista]
Cardini, Andrea Luigi; S., Elton
abstract

Guenons are the most diverse clade of African monkeys. They have varied ecologies, include arboreal and terrestrial species, and can be found in nearly every region of sub-Saharan Africa. Species boundaries are often uncertain, with a variable number of species and subspecies mostly recognised on the basis of their geographic distribution and pelage. If guenon soft tissue patterns show high variability, the same does not seem to hold for skull morphology. Guenon skulls are traditionally considered relatively undifferentiated and homogeneous. However, patterns of variation in skulls have never been examined using a large number of specimens sampled across the breadth of species diversity. Thus, in the present study, skulls of adult guenons and two outgroup species are analysed using three-dimensional geometric morphometrics. Three-dimensional coordinates of 86 anatomical landmarks were measured on 1,315 adult specimens belonging to all living guenon species except Cercopithecus dryas. Species are well-discriminated using shape but the best discrimination occurs when species have either a long evolutionary history (e.g., Allenopithecus nigroviridis) or represent extremes of size variation (Miopithecus sp. and Erythrocebus patas). Interspecific phenetic relationships reflect size differences. Four main clusters are found that mainly correspond to four size groups: the smallest species (Miopithecus sp.), the largest species (E. patas plus the study outgroups), a group of medium-small arboreal guenons, and a group of medium-large arboreal and terrestrial guenons. Correlations between interspecific shape distances and interspecific differences in size are higher than between shape distances and genetic distances. However, if only the component of interspecific shape variation which is not correlated to evolutionary allometry is used in the comparison with genetic distances, correlations are up to 1.4 times larger than those including allometric shape. The smallest correlations are those between shape and ecological distances, which is consistent with the lack of clusters clearly reflecting broad ecological specialisations (e.g., arboreality versus terrestriality). Thus, size, which is generally considered more evolutionarily labile than shape, seems to have played a major role in the evolution of the guenons. The incongruence between interspecific shape differences and phylogeny might be explained by a large proportion of shape changes having occurred along allometric trajectories that tend to be conserved within this clade. (C) 2007 Elsevier Ltd. All rights reserved.

2008 - Variation in guenon skulls (II): sexual dimorphism [Articolo su rivista]
Cardini, Andrea Luigi; S., Elton
abstract

Patterns of size and shape sexual dimorphism in adult guenons were examined using a large sample of skulls from almost all living species. Within species, sexual dimorphism in skull shape follows the direction of size-related shape variation of adults, is proportional to differences in size, and tends to be larger in large-bodied species. Interspecific divergence among shape trajectories, which explain within species sex differences, are small (i.e., trajectories of most species are nearly parallel). Thus, changes in relative proportions of skull regions that account for the distinctive shape of females and males are relatively conserved across species, and their magnitude largely depends on differences in size between sexes. A conservative pattern of size-related sexual dimorphism and a model of interspecific divergence in shape which strongly reflects size differences suggest a major role of size and size-related shape variation in the guenon radiation. It is possible that in the guenons, as in the neotropical primates (with whom they have obvious parallels), size has helped to determine morphological change along lines of least evolutionary resistance, influencing sexual dimorphism. In Miopithecus and Erythrocebus, the smallest and largest guenon genera, it is likely that the interaction of ecology and size contributes significantly to patterns of sexual dimorphism. The results of this study thus emphasise the need to consider allometry and size alongside ecology and behaviour when examining primate sexual dimorphism. (C) 2007 Elsevier Ltd. All rights reserved.

2007 - A geometric morphometric approach to the study of ecogeographical and clinal variation in vervet monkeys [Articolo su rivista]
Cardini, Andrea Luigi; A., Jansson; S., Elton
abstract

Aim To examine and visualize clines in size and shape of Cercopithecus aethiops Linneus, 1758 (Primate, Cercopithecidae) skulls, and to investigate environmental factors which might best explain the observed variation. Location Sub-Saharan Africa. Methods Eighty-six three-dimensional anatomical landmarks were used to describe 306 skulls of adult C. aethiops sampled over its entire distribution. Geometric morphometric methods for the quantitative analysis of form variation were applied. Size and shape variables were computed and regressed onto geographical coordinates and environmental variables (elevation, temperature, rainfall, moisture and Shannon rainfall diversity index) using both linear and curvilinear models. Components (geographical, environmental, spatially structured environmental and residual) of ecogeographical variation in skull form were partitioned using partial regression. A novel approach for summarizing and visualizing nonlinear patterns of clinal variation using surface rendering of three-dimensional shapes is presented. Results Clinal variation in size and shape was highly significant, and was best described by curvilinear models. There were strong similarities between females and males. The cline in size was especially pronounced, explaining up to about 40% of observed variation, and was mainly longitudinal rather than latitudinal. A major trend of clinal shape variation also occurred from west to east, and corresponded to an expansion of the face relative to the neurocranium in the west. In the east, skulls also tended to be deeper and with narrower zygomatic arches. Geography and the spatially structured environmental component were the major contributors to the explained variance in size in both sexes, but the proportion of variance explained by the latter was smaller in females. In contrast, geography and environment explained similar amounts of variation in shape and their contribution was about twice that of the spatially structured environmental component. About 60-80% of variation in skull form was not explained by any variable in the analysis. The main factors influencing skull size differed in females and males, with rainfall being very influential in males. Both female and male skull shapes were strongly affected by average annual rainfall. Main conclusions A strong spatial and environmental basis to variations in African vervet monkey skull form was evident. However, the observed pattern did not conform to predictions based on Bergmann's rule. Rainfall consistently emerged as an important predictor, which may contribute to intraspecific variation in the size and shape of vervet monkey skulls through its effect on habitat productivity.

2007 - Evolution and morphology of Marmota (Rodentia, Sciuridae): ontogeny and interspecific comparison of skulls of all living species [Relazione in Atti di Convegno]
Cardini, Andrea Luigi; Hoffmann, R. S.; O'Higgins, P.; Sala, Luigi; THORINGTON R. W., Jr; Tongiorgi, Paolo
abstract

No aspect of the biology of a species should be neglected if we are to achieve a comprehensive understanding of its evolutionary history. Marmots have been thoroughly used as model organisms by eco-ethologists interested in the evolution of mammal societies. In contrast, phylogenetic and morphological studies have received less attention and have seldom involved all living species. Over the last few years, several studies have been published, which investigate morphological variation in marmots using modern morphometric techniques. These studies have improved our understanding of marmot evolution, supporting subgeneric classifications based on DNA sequences, suggesting an early occurrence of interspecific differences during ontogeny, showing the importance of allometry in the development of age-specific traits, and revealing an unexpected acceleration in the rate of morphological divergence of the youngest and most endangered marmot species, M. vancouverensis. The aim of this paper is to provide the reader with a synthetic overview of these recent advances in the study of marmot biology.

2007 - Evolutionary acceleration in the most endangered mammal of Canada: speciation and divergence in the Vancouver Island marmot (Rodentia, Sciuridae) [Articolo su rivista]
Cardini, Andrea Luigi; R. W. Thorington J., R.; P. D., Polly
abstract

The Vancouver Island marmot is the most endangered mammal of Canada. Factors which have brought this population to the verge of extinction have not yet been fully elucidated, but the effects of deforestation and habitat fragmentation on survival rates, as well as those of variation in rainfall, temperature, snowpack depth and snowmelt strongly suggest that marmots on the island are struggling to keep pace with environmental changes. Genetic analyses, however, seem to indicate that the Vancouver Island marmot may merely represent a melanistic population of its parental species on the mainland. Were it not for its black pelage colour, it is unlikely that it would have attracted much attention as a conservation priority. Our study uses three-dimensional coordinates of cranial landmarks to further assess phenotypic differentiation of the Vancouver Island marmot. A pattern of strong interspecific divergence and low intraspecific variation was found which is consistent with aspects of drift-driven models of speciation. However, the magnitude of shape differences relative to the putatively neutral substitutions in synonymous sites of cytochrome b is too large for being compatible with a simple neutral model. A combination of bottlenecks and selective pressures due to natural and human-induced changes in the environment may offer a parsimonious explanation for the large phenotypic differentiation observed in the species. Our study exemplifies the usefulness of a multidisciplinary approach to the study of biological diversity for a better understanding of evolutionary models and to discover aspects of diversity that may be undetected by using only a few genetic markers to characterize population divergence and uniqueness.

2007 - Mandibular morphology as an indicator of human subadult age: Interlandmark approaches [Articolo su rivista]
D., Franklin; Cardini, Andrea Luigi
abstract

The dentition is widely recognized as the set of developmental markers that appear to show the least variability against chronological age; these markers are thus widely used in forensic anthropological investigations. As a possible alternative, we investigate here the potential of mandibular morphology as a developmental marker for estimating age at death in subadults. The sample analyzed comprises 79 known age and sex subadult individuals of South African Bantu and African American origin. Linear measurements of ramus height were obtained from the mathematical conversion of three-dimensional landmark data. A series of regression analyses were then performed to predict age by using the measurement of ramus height; results were cross-validated using a jackknife procedure. Our results show that ramus height can be used to predict age in the subadult skeleton with accuracy, closely approaching that of standards based on the dentition (standard error rates are between +/- 1.1 years and +/- 2.4 years).

2007 - Sample size and sampling error in geometric morphometric studies of size and shape [Articolo su rivista]
Cardini, Andrea Luigi; S., Elton
abstract

Geometric morphometric studies are increasingly becoming common in systematics and palaeontology. The samples in such studies are often small, due to the paucity of material available for analysis. However, very few studies have tried to assess the impact of sampling error on analytical results. Here, this issue is addressed empirically using repeated randomized selection experiments to build progressively smaller samples from an original dataset of similar to 400 vervet monkey (Cercopithecus aethiops) skulls. Size and shape parameters (including mean size and shape, size and shape variances, angles of allometric trajectories) that are commonly used in geometric morphometric studies, are estimated first in the original sample and then in the random subsamples. Estimates are then compared to give an indication of what is the minimum desirable sample size for each parameter. Mean size, standard deviation of size and variance of shape are found to be fairly accurate even in relatively small samples. In contrast, mean shapes and angles between static allometric trajectories are strongly affected by sampling error. If confirmed in other groups, our findings may have substantial implications for studies of morphological variation in present and fossil species. By performing rarefaction analyses like those presented in our study, morphometricians can be easily provided with important clues on how a simple but crucial factor like sample size can alter results of their studies.

2006 - Postnatal ontogeny of marmot (Rodentia, Sciuridae) crania: Allometric trajectories and species divergence [Articolo su rivista]
Cardini, Andrea Luigi; R. W., Thorington
abstract

Marmots are the largest extant representatives of the squirrel family (Sciuridae). Members of this clade are believed to have conservative skeletal characters and are inclined to convergence in species with similar size and ecology. However, this does not seem to hold for the mandible and cranium of marmots; instead, similarities reflect subgeneric classification or geographic distribution. To understand the pattern of morphological evolution in the genus Marmota, the ontogeny of the cranium is investigated in 7 of the 14 living marmot species. In particular, the role of allometry in producing intra- and interspecific differences is analyzed. Sexual dimorphism in allometric trajectories is found to be negligible, whereas shape traits that characterize a specific age are mostly allometric. Allometry accounts for an important proportion, although not for the majority, of shape variation during postnatal ontogeny of the cranium. Interspecific differences in allometric trajectories are generally small and the majority of shape differences in relation to phylogeny appear early in ontogeny. Thus, allometry might have had a limited role in producing the morphological variation of living marmot species or it might even have constrained the range of evolutionary changes in this clade. A very different role of allometry as a source of morphological novelties can be speculated to exist in earlier stages of man-not evolutionary history, when a highly distinctive cranial shape evolved concomitant with a 2-fold increase in size. Three sets of analyses are performed to investigate the ontogeny of cranial form in Marmota. Three-dimensional (3D) coordinates of anatomical landmarks are used to describe the whole man-not cranium in the first 3D geometric morphometric analysis of a sciurid taxon. Also, anatomical landmarks that describe the dorsal and lateral sides of the cranium are used for 2-dimensional (2D) analyses complementary to previous studies on the ventral cranium. Despite the complexity of the cranium, which makes it a poor candidate for 2D studies, results of 2D and 3D analyses are generally in good agreement.

2006 - Static allometry, species discrimination and sexual dimorphism of guenons (Primates, Cercopithecinae): a three-dimensional morphometric analysis of the skull [Abstract in Rivista]
Cardini, Andrea Luigi; P., O'Higgins; S., Elton
abstract

2005 - Morphological evolution in marmots (Rodentia, Sciuridae): size and shape of the dorsal and lateral surfaces of the cranium [Articolo su rivista]
Cardini, Andrea Luigi; R. S., Hoffmann; R. W., Thorington
abstract

Marmots are the largest ground squirrels and have been extensively studied by sociobiologists investigating the evolution of mammal societies. Being a member of the sciurid clade, traditionally considered inclined to convergence, they are also a group on which to test the hypothesis of sciurid propensity to homoplasy of osteological characters. In the present analysis, the dorsal and lateral surfaces of the cranium of all living marmot species are compared with geometric morphometric techniques. Phenetic groups are found which reflect the subgeneric classification of marmots and are consistent with previous morphometric analyses of the mandible and ventral cranium. Two species have distinctive morphologies and phenetic relationships not congruent with phylogeny. Marmota vancouverensis is highly divergent for osteological characters, fur colour and behaviour despite its young age and close genetic similarity to Marmota caligata. Its small population may represent a rare chance to study evolutionary processes during rapid allopatric speciation in mammals, but strong conservation efforts are required to preserve this unique component of the Vancouver Island biodiversity. Also, Marmota monax has distinctive cranial traits. These are possibly related to its long separate evolutionary history and unique ecology and behaviour. Size-related convergence is not evident in Marmota. When outgroup species are included, Spermophilus, Cynomys, Tamias, and Sciurus group together on one branch, Marmota on the other. This is best explained as a retention of the ancestral morphology in the smaller members of the Marmotini (Spermophilus, Cynomys, and Tamias) and the evolution of derived morphology in Marmota.

2005 - Post-natal ontogeny of the mandible and ventral cranium in Marmota species (Rodentia, Sciuridae): allometry and phylogeny [Articolo su rivista]
Cardini, Andrea Luigi; P., O'Higgins
abstract

Post-natal ontogenetic variation of the marmot mandible and ventral cranium is investigated in two species of the subgenus Petromarmota (M. caligata, M. flaviventris) and four species of the subgenus Marmota (M. caudata, M. himalayana, M. marmota, M. monax). Relationships between size and shape are analysed using geometric morphometric techniques. Sexual dimorphism is negligible, allometry explains the main changes in shape during growth, and males and females manifest similar allometric trajectories. Anatomical regions affected by size-related shape variation are similar in different species, but allometric trajectories are divergent. The largest modifications of the mandible and ventral cranium occur in regions directly involved in the mechanics of mastication. Relative to other anatomical regions, the size of areas of muscle insertion increases, while the size of sense organs, nerves and teeth generally decreases. Epigenetic factors, developmental constraints and size variation were found to be the major contributors in producing the observed allometric patterns. A phylogenetic signal was not evident in the comparison of allometric trajectories, but traits that allow discrimination of the Palaearctic marmots from the Nearctic species of Petromarmota are present early in development and are conserved during post-natal ontogeny.

2004 - Evolution of marmots (Rodentia, Sciuridae): combining information on labial and lingual sides of the mandible [Articolo su rivista]
Cardini, Andrea Luigi
abstract

The morphology of the lingual side of the mandible was analysed in the genus Marmota. Adults from 12 of 14 living species were compared using geometric morphometric techniques. The information on the lingual side was then combined with that of the labial side from a previous analysis. The combined dataset is the most complete description of a marmot mandible ever used in an interspecific comparison in this genus and it represents the second morphological study ever realized that includes a large sample with all marmot species. The study confirmed the uniqueness of M. vancouverensis for mandible morphology, with atypical traits likely to have evolved in a relatively young but small population of marmots isolated on the Vancouver Island since the end of the Pleistocene (10 000-100 000 ybp), stressing the importance of a strong effort to save this species from extinction. Marmota olympus also has a distinctive mandibular trait undetected in a previous analysis using information on the lingual side only. The Olympic marmot has a longer evolutionary history but it is presently found only in the Olympic Peninsula and shares with M. vancouverensis a similar history of geographic isolation and population bottlenecks. Genetic bottlenecks might have profoundly affected marmot morphological evolution and may have increased the rate of shape change in marmot radiations. Both the analysis of the lingual side alone and the combined dataset (lingual and labial information) failed to clearly discriminate the two main marmot subgenera but the combined description of the mandible supports the similarity of the two main species (M. caligata and M. flaviventris) of the subgenus Petromarmota, and the proximity of the North American M. monax to Palaearctic marmots. Surprisingly, the analysis of the lingual side indicated that M. canitschatica and M. marmota have unusual traits for the subgenus Marmota. At least for the latter species, this finding is congruent with peculiarities in fur and parasitic relationships, and may be related to an ancient phylogenetic origin for M. marmota.

2004 - Mandibular shape in the genus Marmota (Rodentia, Sciuridae): a preliminary analysis using outlines [Articolo su rivista]
Cardini, Andrea Luigi; D. E., Slice
abstract

Marmots are of prominent interest for sociobiologists studying mammal societies. They are also a fascinating group on which to test congruence between morphological information and molecular phylogeny and the possible occurrence of hemoplasy in the evolution of the sciurid skeleton. To investigate marmot morphological relationships, an analysis of the outlines of the posterior region of the marmot mandible was performed using Elliptic Fourier analysis. Outgroup species belonging to other sciurid genera were also included, and the efficacy of this technique to discriminate taxa based on the morphology of this mandibular region was assessed. The mandible outlines led to a partial separation of the groups under study, but the phylogenetic signal seems to be weak compared to previous studies of the marmot mandible. indeed, epigenetic influences acting on the posterior region of the mandible, an area of insertion of important masticatory muscles, may be a source of phenotypic variation that can mask the phylogenetic signal. However, interpretations must be made with caution as the posterior region of the mandible is an apparently suitable structure for outline analysis but the poor alignment of the outlines using standard elliptic Fourier methods made the study more complex than expected.

2004 - Patterns of morphological evolution in Marmota (Rodentia, Sciuridae): geometric morphometrics of the cranium in the context of marmot phylogeny, ecology and conservation [Articolo su rivista]
Cardini, Andrea Luigi; P., O'Higgins
abstract

Marmots are of great interest for both sociobiologists studying the evolution of mammal societies and conservationists trying to protect them from extinction. In contrast, their phylogeny and morphological evolution are poorly understood and studied. Recently, a phylogenetic analysis using cytochrome b provided the first reconstruction of marmot evolutionary history and suggested that a high level of sociality evolved at least twice independently in the two proposed marmot subgenera. A morphological analysis of the marmot mandible supported this subgeneric classification and showed interesting, and unexpected, patterns in the evolution of marmot skeletal characters. In the present study we investigated a more complex, and potentially informative structure, the ventral cranium. Geometric morphometric techniques were applied in the first analysis of cranial morphology including all marmot species. Three main phenetic groups were found, which reflect phylogeny (subgenus Petromarmota, and Palaearctic subgenus Marmota) or geographical distribution (Palaearctic vs. Nearctic subgenus Marmota). Convergence in skeletal characters due to size similarities, a common finding in the sciurid skeleton according to traditional morphological analyses, did not occur in the marmot ventral cranium. Despite a genetic distance between Marmota vancouverensis and Marmota caligata similar to that among different populations of the latter species, the Vancouver Island marmot had the most atypical ventral cranium in the subgenus Petromarmota. This finding confirmed results obtained with the mandible, and emphasized the uniqueness of M. vancouverensis and the usefulness of complementing molecular analyses with morphological studies for a thorough characterization of population divergence, and a careful planning of conservation strategies. (C) 2004 The Linnean Society of London.

2004 - Shape diversity in the trophi of different species of Rotaria (Rotifera, Bdelloidea): a geometric morphometric study [Articolo su rivista]
D., Fontaneto; G., Melone; Cardini, Andrea Luigi
abstract

Rotifers have articulated hard jaws called "trophi", whose shapes are considered species-specific for monogonont rotifers but not for bdelloid rotifers. We present a geometric morphometric analysis of size and shape of bdelloid jaws, carried out on SEM pictures of trophi of nine morphospecies belonging to the genus Rotaria, using six landmarks. The Study Shows that trophi call also have species-specific form in bdelloids and suggests future directions for the analysis of the relationship between shape, size and diet in modelling trophi morphology during the evolution of Rotaria.

2004 - The phylogeny of Branchiobdellida (Annelida, Clitellata) assessed by sperm characters [Articolo su rivista]
Cardini, Andrea Luigi; M., Ferraguti
abstract

Data on the spermatozoa of Branchiobdellida were taken from the published literature: sperm models of 25 species belonging to 13 different branchiobdellidan genera have been compared with the aim of supplying further evidences for a phylogenetic analysis of the group. The species considered were representative of all traditional branchiobdellidan families, excluding the monotypic Caridinophilidae. Branchiobdellidan spermatozoa are complex cells, thus it was possible to analyse the variation of 20 characters within the group. A parsimony analysis has yielded nine minimal trees, eight of which are very similar to one another. The main conclusions of the phylogenetic analysis are: (a) the monophyly of the taxon Branchiobdellida is confirmed; (b) the most speciose branchiobdellidan genus, Cambarincola is polyphyletic; (c) none of the traditional 'families' are supported; (d) the genus Branchiobdella is monophyletic, but the position of one species, B. kobayashi, albeit basal to the whole genus, is not resolved; (e) the other two genera analysed for which more than one species was available, Pterodrilus and Xironogiton, are monophyletic; (f) there seems to be a 'trend' in the whole group towards an increase of acrosome length. Our results partly parallel those obtained by Gelder and Siddall (2000) with a combined analysis of molecular and somatic characters, and point to the need for a comprehensive revision of the Branchiobdellida based on a combination of molecular, somatic and spermatological data sets. (C) 2004 Elsevier GmbH. All rights reserved.

2003 - Skull form and evolution in Marmota (Rodentia, Sciuridae). [Relazione in Atti di Convegno]
Cardini, Andrea Luigi; Tongiorgi, Paolo; Sala, Luigi; O'Higgins, P.
abstract

A geometric morphometric analysis of the form of the marmot ventral cranium and mandible was carried out. Allometry was found to play an important role in shaping both these structures, and, although allometric trajectories were species-specific, similar shape changes were observed during ventral cranial and mandibular growth. Most of the ontogenetic shape changes occur in regions involved in the mechanics of mastication and bite. Sexual dimorphism is manifest mainly size. The interspecific comparison of ventral crania from all living marmot species produces results only partially congruent with those obtained for the mandible or with the marmot molecular phylogeny. The phylogenetic signal in the ventral cranium seems weaker than in the mandible, and the morphological clusters do not reflect evident size or ecological similarities. The ventral cranium could have limited evolutionary plasticity due to its complexity, and, thus, it may have retained plesiomorphic characters which contribute to mask the phylogenetic signal.

2003 - The geometry of the marmot (Rodentia : Sciuridae) mandible: Phylogeny and patterns of morphological evolution [Articolo su rivista]
Cardini, Andrea Luigi
abstract

Marmots have a prominent role in the study of mammalian social evolution, but only recently has their systematics received the attention it deserves if sociobiological studies are to be placed in a phylogenetic context. Sciurid morphology can be used as model to test the congruence between morphological change and phylogeny because sciurid skeletal characters are considered to be inclined to convergence. However, no morphological study involving all marmot species has ever been undertaken. Geometric morphometric techniques were applied in a comparative study of the marmot mandible. The adults of all 14 living marmot species were compared, and mean mandible shape were used to investigate morphological evolution in the genus Marmota. Three major trends were observed. First, the phylogenetic signal in the variation of landmark geometry, which describes mandible morphology, seems to account for the shape differences at intermediate taxonomic levels. The subgenera Marmota and Petromarmota, recently proposed on the basis of mitochondrial cytochrome b sequence, receive support from mandible morphology. When other sciurid genera were included in the analysis, the monophyly of the genus Marmota and that of the tribe Marmotini (i.e., marmots, prairie dogs, and ground squirrels) was strengthened by the morphological data. Second, the marmotine mandible may have evolved as a mosaic of characters and does not show convergence determined by size similarities. Third, allopatric speciation in peripheral isolates may have acted as a powerful force for modeling shape. This hypothesis is strongly supported by the peculiar mandible of M. vancouverensis and, to a lesser degree, by that of M. olympus, both thought to have originated as isolated populations in Pleistocene ice-free refugia.

2003 - Yellow-bellied marmots (Marmota flaviventris) 'in the shape space' (Rodentia, Sciuridae): sexual dimorphism, growth and allometry of the mandible [Articolo su rivista]
Cardini, Andrea Luigi; P., Tongiorgi
abstract

Geometric morphometrics was applied in a quantitative analysis of the morphology of the yellow-bellied marmot mandible. Five age classes were recognised by premolar toothwear, and the size and shape of the lower jaw were compared between sexes and among ages. Although the social role of adult males and females is markedly distinct, with the former mainly engaged to defend a territory with a female harem and the latter taking care of the young, mandible sexual dimorphism was moderate. On the contrary, form differences among age classes were conspicuous, and ontogenetic scaling, aimed at increasing mandible robustness, accounted for the majority of the shape change during growth. At least one mandibular shape modification, however, was related to the different behavioural ecology of immature and adult marmots. The mechanical efficiency of the superficial masseter and, thus, the strength of the incisor bite become so much greater in the sexually mature individuals that it cannot be interpreted as size-related adjustment. The need for stronger incisive bites is not explained by diet change, as the yellow-bellied marmot adults feed on the same grasses and forbs as the young and yearlings. Increasing the strength of the incisor bite is likely to be adaptive in order to provide adults with more efficient 'weapons' for intraspecific conflicts, and self- and kin-defence from predators. Morphological remodelling in the yellow-bellied marmot mandible seems to be more concerned with changes in size and behaviour during growth than with ethological differences between adults of the two sexes.

2001 - Crescita e forma in Marmota (Rodentia, Sciuridae): la morfometria geometrica della mandibola nell'indagine ontogenetica e filogenetica. [Altro]
Cardini, Andrea Luigi
abstract

2000 - A phylogenetic assessment of the branchiobdellidan family Branchiobdellidae (Annelida, Clitellata) using spermatological and somatic characters [Articolo su rivista]
Cardini, Andrea Luigi; M., Ferraguti; S. R., Gelder
abstract

The spermatozoa of six species belonging to the branchiobdellidan family Branchiobdellidae (i.e. Xironogiton victoriensis, Cirrodrilus kawamurai, Ankyrodrilus legaeus, Xironodrilus formosus, Branchiobdella kobayashii, Branchiobdella orientalis) were studied and compared to the other sperma-tozoa already described in the group. A parsimony analysis was performed on the spermatozoal data of the species examined, as well as on their somatic characters. The results of the two analyses were contrasted and a further parsimony analysis was run on the matrix comprising both sets of characters. The study of sperm ultrastructure confirmed the genera recognized with traditional somatic characters and the monophyly of the branchiobdellidans. Xironodrilus was proved to be the sister species of Ankyrodrilus and its inclusion into the family Branchiobdellidae was supported. Evolutionary hypotheses on intergeneric differences in the family consistent with its biogeography can be suggested by the cladograms: Xironogiton is an early offshoot of branchiobdellidan lineage migrating to North America and probably radiating only in recent times; Branchiobdella kobayashii has a spermatozoon completely different from that of the other species of the genus, thus suggesting a complex story for this widespread taxon with a disjunct distribution.

Università degli studi di Modena e Reggio Emilia

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