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Session Schedule & Abstracts

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Friday 1st July, 2016

Geometric Morphometrics 1

Room: Salon C   9:30 am–11:00 am

Moderator(s): Kirchner-Smith ME, Tinius A
GMM1-1  9:30 am  Morphological responses of the scapula and os coxae to selection for high voluntary locomotor activity in laboratory mice (Mus musculus domesticus, Rodentia: Muridae). Schutz H*, Pacific Lutheran University; Jamniczky H.A., Cumming School of Medicine, University of Calgary; Asplund C.L., Pacific Lutheran University; Braaten-Fierros K, Pacific Lutheran University; Higginbotham C, Pacific Lutheran University; Donovan Edward, Pacific Lutheran University; Garland T, University of California, Riverside
Abstract: In mammals, the major girdle elements (scapula and os oxae) serve as attachment sites for muscles powering locomotion and in females, the os coxae also forms much of the bony birth canal. Previous comparative work shows that scapular and coxal morphology reflect variation in locomotor function. However, few studies differential responses in these elements similar locomotor variation. Additionally, sexual dimorphism of the os coxae is common in mammals and numerous studies suggest that this dimorphism results from an evolutionary trade-off between reproduction and locomotion but the potential performance trade-offs are difficult to demonstrate. Given the importance of their functional roles, the scapula and os coxae can greatly inform our understanding of both morphological responses to changes in locomotor behavior and potential trade-offs between different functions, yet much of the work done to understand these questions is comparative in nature, presenting some limitations. To add to the existing knowledge of these patterns of scapular and coxal morphology, we employ an experimental evolutionary approach by using laboratory mice bred for high voluntary wheel running (HR) and from non-selected control (C) lines to investigate how selection for high locomotor activity differentially affects the morphologies of the scapula and os coxae as well as variation in the magnitude of sexual dimorphism in the os coxae. Specifically we used geometric morphometric analyses of the os coxae and scapula in a sample of male mice. We then used both geometric morphometrics and X-ray micro computed tomography to measure differences in the shape and in bone mineral density and bone volume of the os coxae in a sample of male and female mice. Our results indicate that the scapula and os coxae differ in the magnitude of their response to selection and that dimorphism of the os coxae differs with selection, but the trajectories of those differences were not as predicted.

GMM1-2  9:45 am  Using 3D geometric morphometrics to study interspecific variation in the forelimb of modern tapirs (Perissodactyla: Tapirus). MacLaren J. A.*, Universiteit Antwerpen; Aerts P., Universiteit Antwerpen; Nauwelaerts S., Universiteit Antwerpen
Abstract: Forelimb morphology is an indicator for terrestrial locomotor ecology. The limb morphology of the enigmatic tapir (Perissodactyla: Tapirus) has often been compared to that of basal perissodactyls, despite no quantitative studies comparing forelimb variation in modern tapirs. Here, we present a quantitative assessment of tapir forelimb osteology using three-dimensional geometric morphometrics to test whether the four modern tapir species are monomorphic in their forelimb skeleton. The shape of the scapula, humerus, radius and ulna of 24 individuals across the four species (T. indicus; T. bairdii; T. terrestris; T. pinchaque) was investigated. Bones were laser scanned to capture surface shape. 3D landmark analysis was used to quantify bone shape. Discriminant function analyses were performed to reveal landmarks which can be used in interspecific discriminations. Overall our results show that the appendicular skeleton contains notable interspecific differences. Our results demonstrate that upper forelimb bones can be used to discriminate between species (>91% accuracy), with the scapula proving the most diagnostic bone (100% accuracy). Features that most successfully discriminate between the four species include the placement of the cranial angle of the scapula, depth of the condylus humeri, and the lateral fovea capitis radii. Overall, the mountain tapir T. pinchaque most consistently exhibits the greatest divergence in morphology from the other three species. Despite previous studies describing all tapirs as functionally mediportal in their locomotor style, we find osteological evidence of a spectrum of locomotor morphology in the genus Tapirus. We conclude that the four extant tapir species differ in upper forelimb osteology; they are neither monomorphic, nor are they as conserved in their locomotor habits as previously described.

GMM1-3  10:00 am  3-D geometric morphometric exploration of pelvic girdle configuration in four ecomorphs of Greater Antillean anoles (Squamata: Dactyloidae). Tinius A*, University of Calgary; Russell A, University of Calgary
Abstract: Anoline lizards of the Greater Antillean islands have featured prominently in studies of convergent evolution, and have become a focal taxon for the study of ecomorphology. External morphological traits vary in association with exploitation of different portions of the structural habitat, and much of this variation is associated with the locomotor system. Previous morphological studies of the shoulder girdle of island anoles revealed that the 3-D form of isolated girdle elements differs markedly between anoline ecomorphs from Hispaniola and Puerto Rico, although girdle structure is relatively conservative in Jamaican anoles. Here we apply 3-D geometric morphometric approaches to the analysis of the in situ pelvic girdle of twenty-six species of anoles, belonging to the only four ecomorphs common to Jamaica, Puerto Rico and Hispaniola. Our investigations reveal subtle differences in the morphology of the pelvic girdle between anole ecomorphs. The structural differentiation of the pelvic girdle is less prominent than predicted based upon an earlier study of the pectoral girdle. Structural differences in the pelvic girdle are evident consistently, however, in anoles from all three islands. Twig anoles, in particular, are characterised by a relatively elongated ilium, an anteroposteriorly shortened pubis, and a greater anteroventral inclination of the pubic apron, when compared to the other ecomorphs. Trunk-crown anoles show a more posteriorly positioned ilium, with a greater anteroventral inclination. This differentiation in form likely relates to changes in the direction of muscle vectors, thus representing skeletal-morphological adaptations associated with differences in locomotor style and habitat use.

GMM1-4  10:15 am  How good is the tarsometatarsus for species identification? 3D Geometric Morphometrics in living and extinct foot-propelled diving birds. Kirchner-Smith M.E.*, University of California, Berkeley
Abstract: Hesperornithiformes (Aves: Ornithurae) were flightless foot-propelled diving birds that lived during the Late Cretaceous and have an excellent fossil record compared to most Mesozoic birds. Extinct bird taxa are often identified from fragmentary or isolated specimens, and several species of Hesperornis have been named on the basis of the tarsometatarsus alone. Size has often been the criterion for taxonomic differentiation, but little has been done to examine intraspecific factors that determine the form of this bone. To test for intraspecific and interspecific variation in the tarsometatarsus of hesperornithiforms, I examined variation in extant members of the foot-propelled diving Gaviidae (loons) and Podicipedidae (grebes). Loons and grebes are morphologically similar to extinct hesperornithiforms, making them appropriate analogues, even if we cannot assume homologous levels of variability in the two groups. Only adult female specimens were chosen for analysis, to reduce the possibility of sexual dimorphism or ontogenetic differences. I used landmark-based Geometric Morphometrics to analyze 3D scans of specimens from three species per family, totaling 22 extant specimens. Thirteen individuals from five named species of Hesperornis were also used. Separate analyses were performed on the shape of the full bone, the shape of the distal end, and the shape of the proximal end for each clade (Gaviidae, Podicipedidae, and Hesperornis). In nearly every Principal Component Analysis of extant and extinct groups, individuals did not group by species, and any “taxonomic” grouping recovered was poorly defined. These results indicate that intraspecific variation swamps interspecific variation in foot-propelled divers, and so the tarsometatarsus alone is not a reliable taxonomic guide. Therefore published taxonomic schemes of named hesperornithiforms based solely or mainly on tarsometatarsi should not be used in studies of diversity.

GMM1-5  10:30 am  Femoral neck bone density and morpho-functional feature in chimpanzees. Matsumura A*, National Defense Medical College; Okada M, Tsukuba University
Abstract: Morphology of bone well reflects daily behavior of animals. In the past studies, it is known that the cortical thicknesses of the femoral neck inferior regions are larger than the superior region in chimpanzees, but not so conspicuous in humans (Matsumura et al., 2010, Int. J. Primatol.). In order to confirm the mechanical effects of daily locomotion on the femoral neck of chimpanzees (Pan troglodytes), we examined the relationships between the density and thickness of cortical bone along the circumference in a cross-section of femoral neck. Femora from captive chimpanzees (specimens of Dokkyo Medical University; n=8) were used in this study. We obtained serial scans of 5 parts along the femoral neck, perpendicular to its long axis by using pQCT (XCT Research SA+, Stratec Medizintechnik GmbH). In each cross-section, data of cortical thickness were measured in 8 parts at every 45 degrees around the circumference. Data of cortical density were measured in 8 regions of ROI corresponding to the measurement parts of cortical thickness. Cortical density of femoral neck around mid-region showed lower values in the superior parts of every individual. The average density tended to show the smallest value in the superior part where cortical thickness was the smallest, and showed relatively small tendency in antero-superior region where cortical thickness was the second largest. In contrast, the density around anterior, inferior, and posterior regions showed relatively higher and almost constant values compared to the superior region while the values of density in the superior region had large dispersion. These results confirmed that the burdening of femoral neck of chimpanzees borne in daily locomotion is smaller in the superior parts compared to other parts. The results of the present study also indicate that cortical area and thickness reflect the strengthening of femoral neck rather than the cortical density against various loads.

GMM1-6  10:45 am  Ontogenetic changes in muscle architectural properties in the Eastern cottontail rabbit (Sylvilagus floridanus). Butcher MT*, Youngstown State University; Rose JA, Youngstown State University; Glenn ZD, Youngstown State University; Tatomirovich NM, Youngstown State University; Foster AD, NEOMED; Smith GA, Kent State University at Stark; Young JW, NEOMED
Abstract: Rabbits have fast-contracting muscles that allow them to accelerate rapidly. Moreover, juveniles may have performance advantages relative to adults that could increase their chances of escaping predation. We predicted that force and power capacity of the extensor musculature would be optimized in juvenile rabbits, allowing them to achieve levels of locomotor performance similar to, or even greater than, that of adults. To test this hypothesis, we quantified muscle architectural properties across ontogeny in Eastern cottontail rabbits (Sylvilagus floridanus). Measurements of muscle mass (MM), belly length (ML), fascicle length (LF), pennation angle, and physiological cross-sectional area (PSCA) were taken from each muscle, and these metrics were used to calculate functional estimates of maximum isometric force, joint torque, and instantaneous power. The scaling results did not support our hypothesis. Relative to body mass, extensor group MM and estimates of instantaneous power scale with positive allometry. However, juvenile rabbits may have several compensatory features that may allow for increased performance (and fitness) including higher LF/ML ratios, and greater effective mechanical advantage at the hindlimb joints. Therefore, development of their musculoskeletal system appears to provide juvenile rabbits with some advantages to evade predation by rapid acceleration. By contrast, adult rabbits may require positive allometry of muscle power in order to cope with greater absolute body size and associated limits on acceleration capacity. Supported by NSF IOS-1147044 and NEOMED.

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