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Session Schedule & Abstracts

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Friday 1st July, 2016

Geometric Morphometrics 2

Room: Salon C   11:30 am–1:00 pm

Moderator(s): Fruciano C, Stayton CT
GMM2-1  11:30 am  Quantitative morphological convergence and divergence of carnivorous rodents from the Indo-Pacific. Fabre P-H*, Institut des Sciences de l'Evolution de Montpellier (ISEM - UMR 5554 UM2-CNRS-IRD); Rowe K, Museum Victoria; Achmadi A, LIPI, Museum Zoologicum Bogoriense; Esselstyn J, Lousiana State University, Museum of Natural Science
Abstract: Convergence – the independent acquisition of similar characters across different lineages that did not share a common biological background – is a prime example to demonstrate the strength of extrinsic factors that might deterministically shape phenotypic evolution. Natural selection factors have often drive exceptional morphological convergences among unrelated organisms. Several placentals are famous to have independently evolved herbivorans, nectarivorans, insectivorans or carnivorans convergent adaptations highlighting the dietary constraint on their cranio-dental morphologies. Among the most spectacular dietary change of ecology and morphology are the shift toward termitophagy and vermivorry found several independent lineages. Rodents of the family Muridae (rats and mice) have migrated from Asia to the major landmasses of the Indo-Pacific archipelago (IPA) multiple times since the Miocene. Their ecological diversity is facilitated by a remarkable array of morphologies, including some associated with unique niche shifts toward an animalivorous diet. Our study focus on four independent acquisitions of animalivory in the Indo-Pacific using an exhaustive murine sampling for this region and provide what is to date the most thorough examination of a mammal adaptive radiation involving a spectacular change of morphology and ecology. We obtained a new integrative framework on morphology, molecules, ecology and phylogeny from animalivoran rodents from all the Indo-Pacific area, comprising two thousand specimens from 221 murine species for jaw and skull. Demonstrating quantitative convergence among independent lineages is challenging. Morphological similarities among unrelated lineages may be qualitatively apparent but not reflect quantitative convergence of traits. Using recent comparative methods and a large dataset containing both ecomorphological and phylogenetical data we were able to infer the quantitative convergence among these animalivoran IPA murines.

GMM2-2  11:45 am  Morphometric models for estimating bite force in murid rodents: empirical versus analytical models. Ginot S*, ISE-M; Hautier L, ISE-M; Herrel A, MNHN; Claude J, ISE-M
Abstract: Bite force is an ecologically significant performance trait that can be readily measured using an ad hoc device. However, it may also be derived from bone morphology either with simple models using muscular levers or more complex ones relying on geometric morphometrics. We quantified morphologies and measured bite force in different rodent species (Muridae), in the wild and in the lab, to better understand the relationship between performance and morphology. Using geometric morphometric data, we produced several predictive models uniting bite force with morphology at different evolutionary scales. These empirical models were compared with an analytical one, based on muscular lever and mechanical advantage. We first looked at how bite force and mandible morphology change throughout ontogeny in lab-reared pups of Mus musculus domesticus at different stages from 15 (just after incisor eruption) to 68 days (maturity). Then, we analysed mandible shape and bite force variation/covariation in four wild species of Muridae: Rattus exulans, Rattus tanezumi, Mus cervicolor, and Mus cookii. This allowed us to estimate the divergence among intraspecific and interspecific patterns of covariation of mandible shape with bite force. Finally, in order to estimate the best approach, we applied our predictive models to other individuals and species and interpreted the deviations between observed bite force and predicted bite force with regard to ecological and behavioural factors (e.g. differences in aggressiveness, commensalism...).

GMM2-3  12:00 pm  Darwin’s Niata - an anatomical, morphometric, and genetic study of an extinct cattle breed: expanding morphological boundaries through selective breeding. Veitschegger K*, Paläontologisches Institut und Museum, University of Zürich, Zürich, Switzerland; Wilson LAB, School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, New South Wales, Australia; Camenisch G, Institute of Evolutionary Biology and Environmental Studies, University of Zürich, Zürich, Switzerland; Keller LF, Institute of Evolutionary Biology and Environmental Studies, University of Zürich, Zürich, Switzerland; Sánchez-Villagra MR, Paläontologisches Institut und Museum, University of Zürich, Zürich, Switzerland
Abstract: Domestication can produce phenotypes that expand the morphospace occupied by wild forms, providing case studies of rapid evolution and morphological transformation. An example is the now extinct Niata cattle form, its peculiar features having been the subject of discussion and argumentation in the writings on evolution by Charles Darwin. The Niata cattle form has been considered an achondroplastic dwarf, an oddity of selective breeding, and, owing to its atypical jaw shape, a non-viable variation of cattle. We explored the validity of these hypotheses, and the proposed unique features of the Niata cattle, by combining morphological, geometric morphometric, and genetic approaches. Using a sample of 87 breeds as comparison, we analyzed landmark data of 340 skulls, cranial suture closure data of 27 sutures, applied Finite Element Analysis (FEA) to 3D virtual models of the skull to evaluate feeding biomechanics, and extracted genetic data using SNiP sequencing methods. Our results reveal that the Niata cattle have very distinctive anatomical features that are unique to this taurine breed. Niata cattle occupy a very distinct position in morphospace owing to their short snout and high forehead, features that are much less pronounced in other classical brachycephalic cattle breeds. Although the Niata was described by some as an achondroplastic dwarf, it does not fit the morphological characteristics of this congenital disease. The size, postcranial skeleton, and external suture obliteration in diagnostic parts of the skull contradict this hypothesis. In conclusion, the Niata was a viable variation of cattle that is as much part of the potential morphospace of cattle as is the bulldog for dogs. The rarity of the morphological traits of the Niata in cattle seems to be the result of human preference and a misinformed interpretation of skull features that are reminiscent of the “snorter dwarf” condition, which is the general term for a lethal form of achondroplasia in cattle.

GMM2-4  12:15 pm  Physical media influence the rate and pattern of turtle carapace shape evolution. Djurakic M*, University of Novi Sad, Faculty of Sciences, Department of Biology and Ecology; Herrel A, UMR 7179 CNRS/MNHN Départment d'Ecologie et de Gestion de la Biodiversité
Abstract: Aquatic and terrestrial environments subject organisms to considerably different selective pressures because water is about 800 denser and 50 times more viscous than air. Therefore, it is not surprising that even remotely related aquatic animals resemble each other in form and function as the morphological solutions to the functional requirements are limited by mechanical constraints. However, how the physical environment influences the rate of morphological evolution is largely unknown. Here we tackle this question by comparing the rate and pattern of the carapace shape evolution between aquatic, semi-aquatic and terrestrial turtles. Shell shape was quantified by 3D geometric morphometrics, and rates of shape evolution were compared using a time-calibrated molecular phylogeny. Patterns of shape evolution were examined by comparing evolutionary rates for upper- (vertebral and costal plates) and lower-carapace (marginal plates) relative to the physical environment. The first phylogenetic principal component showed a gradient from terrestrial to aquatic turtles highlighting the correlated evolution of morphology with the physical environment. Whole shell shape showed a greater evolutionary rate for terrestrial turtles compared to aquatic ones. Although terrestrial turtles exhibited greater rates for both carapace parts compared to aquatic turtles, statistical significance was obtained only for the lower-carapace. While the terrestrial environment favors a tall, well developed lower-carapace, this part of the shell is unfavorable in aquatic media. As a consequence, aquatic turtles exhibited a greater evolutionary rate for the upper carapace compared to the lower part, while the opposite pattern was observed for terrestrial turtles. Semi-aquatic turtles showed same evolutionary rates for both parts. Results suggest that biomechanical constraint of two physical media influence rate and pattern of turtle carapace shape evolution.

GMM2-5  12:30 pm  Patterns of morphological and mechanical evolution in the turtle shell. Stayton CT*, Bucknell University   tstayton@bucknell.edi
Abstract: Turtles provide an excellent opportunity to study the interplay between morphology, functional performance, and diversification. Here turtle shells are used to test hypotheses regarding the influence of functional demands on morphological diversification. The traditional view suggests that structures which perform a greater number of functions will show slower rates of evolution and lower levels of diversification than those which perform fewer functions. More recent hypotheses propose that diversification may be greater in structures which have many functions, where performance cannot be simultaneously optimized on all functions. We test these hypotheses by comparing the diversification patterns of aquatic turtle shells (whose shells must be strong, hydrodynamically efficient, and allow efficient self-righting if overturned) and terrestrial turtle shells (for which hydrodynamic performance is not relevant). We find broad support for the traditional hypothesis: terrestrial shells show greater levels of morphological disparity within and among clades than aquatic shells. However, this is despite higher rates of morphological evolution in aquatic shells. Separate tests on the carapace and plastron on shells further complicate this picture. Analyses of shape-performance relationships in mechanical strength, hydrodynamic efficiency, and righting ability, provides a resolution: functional influences on diversification appear to be strongly influenced by the shapes of performance surfaces. Neither the presence of a single optimum (or even any optimum) morphology, nor the presence of one-to-one mapping of morphology onto performance, can be assumed when examining even modestly complex structures. However, it may be possible to use patterns of evolution to make testable hypotheses about the complex shapes of performance or selective surfaces. This research was funded by NSF-RUI grant IOS-1257142.

GMM2-6  12:45 pm  A look at measurement error in geometric morphometrics. Fruciano C*, Queensland University of Technology; Weisbecker V, University of Queensland; Phillips MJ, Queensland University of Technology
Abstract: Geometric morphometrics – once considered revolutionary – has now reached maturity and is routinely used in ecological and evolutionary studies. However, the presence and the extent of measurement error is often overlooked in empirical studies. Here, using empirical data, we analyse measurement error and bias from different sources (preservation, presentation, digitization, multiple operators). We then apply multiple methods to reduce measurement error. Our results suggest that measurement error is pervasive and often subtle (and for this reason, easy to overlook). We suggest that often multiple approaches should be used to test and account for different sources of measurement error.

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