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Session Schedule & Abstracts

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Thursday 30th June, 2016

Locomotion 1

Room: Salon G   9:30 am–11:00 am

Moderator(s): Fabre A-C, Gibb AC
LOC1-1  9:30 am  Comparing rodent species of different sizes for ecomorphological analyses. Verde Arregoitia L.D.*, Natural History Museum Bern
Abstract: Multispecies comparative analyses can identify the functional relationships between morphology and ecology. In comparisons across multiple species, two methodological issues are controversial because they can alter a study’s results and interpretation: size correction and relative measurements. First, we are usually interested in the interspecific trait differences that remain once differences in overall size have been controlled for. Second, ecologically-relevant characters are often relative measures. For example: in mammals jumping locomotion is associated with increased hind foot length relative to the length of the body. Relative measures (ratios) can lead to data with poor distributional properties and the potential for spurious correlations with ecological data. Combining size correction and relative measures becomes problematic, because the calculation of ratios is not effective for statistical control but is essential for evaluating proportionality. This work explores how the choice of size-related statistical procedures affects ecomorphological analyses. I test the effects of various methods on a set of craniodental, external, and ecological characters for 200 species of rodents from five biogeographic realms, representing all the ecotypes in the order. Relative measurements relate to locomotion mode and feeding strategy better than individual size-corrected traits, but their use requires careful testing of how the variance components behave in a comparative framework. Additionally, comparative analyses across species need to control for the non-independence of species data that arises through patterns of shared common ancestry.

LOC1-2  9:45 am  Coevolution between forelimb shape and loading regime in strepsirrhines. Fabre A-C*, MNHN; Granatosky M C, Duke University; Hanna J, West Virginia School of Osteopathic Medicine; Schmitt D, Duke University
Abstract: Animals can move in similar environments using different locomotor strategies that can be difficult to define using only strict qualitative categories. Despite the interesting results that have come forth from this approach, analyses remain hampered by a lack of quantitative data linking kinematics or kinetics of locomotion to bone shape. Few studies have considered the effect of limb loading on anatomical form directly. In this study we quantify 1) the shape of the forelimb, 2) the loading regime of the forelimb during arboreal locomotion, and 3) the relationship between the shape of the forelimb and the loading regime. Eight species showing substantial variation in the use and morphology of the forelimb, ranging from quadrupedal terrestrial (ring-tailed lemur) to quadrupedal arboreal (Aye Aye) to vertical leaping (Sifaka) were examined. The morphology of the bones of the forelimb was quantified using geometric morphometric approaches and peak loads on the forelimb were recorded as animals walked on an instrumented horizontal pole at the Duke Lemur Center. These data were then used to quantitatively link locomotor behavior, morphology, body mass and mechanics using covariation analyses in a phylogenetic comparative framework (2B-PLS and phylogenetic 2B-PLS). Our results show strong anatomical differences between slow quadrupedal climbers, vertical leapers and quadrupedal species in the shape of the long bones of the forelimb. Loading regimes were also different between animals with different locomotor strategies. A strong covariation between long bone shape and loading regime was detected even when taking into account the phylogeny. The covariation between shape and mechanical demands was stronger in bones involved in load transfer (humerus and ulna) compared to the radius. This project was supported by an NSF BCS 0749314 grant, the Leakey and Force and Motion Foundation, Fondation Fyssen and the Marie-Skodowska Curie fellowship (EU project 655694 - GETAGRIP)

LOC1-3  10:00 am  Limb specializations and adaptive diversification in Mustelidae. Kilbourne BM*, Museum für Naturkunde Berlin
Abstract: Mustelidae, a carnivoran clade of ~60 species consisting of weasels, otters, badgers, and martens, exhibit a diversity of locomotor habits, including climbing, digging, and swimming. The combined functional diversity and species richness of Mustelidae make this clade an ideal group in which to test whether primary locomotor habit constitutes a selective regime acting upon limb morphology. To quantify limb skeletal morphology, I performed a principal component analysis on 28 variables reflecting bone robustness and muscle moment arms for a sample of 36 mustelid species. The scores for each taxon along PC axes 1 to 3 were then fitted to models of trait diversification. Using Ornstein-Uhlenbeck models, I tested whether single and multi-optima models of adaptive diversification best describe the variation in limb skeletal morphology, with multi-optima models reflecting selective regimes for locomotor habit and differences in body size. Additionally, single and multi-rate models of Brownian motion were also tested. PC-1, which represents 95% of the variance, is a measure of taxon size. PC-2 and PC-3 respectively represent 2 and 1% of the variance yet distinguish climbing, digging, and swimming specialists. Notably PC-2 represents a trade-off between bone gracility and robustness, whereas PC-3 represents an elongation of the deltoid tuberosity, olecranon process, and greater trochanter. The variance in PC-1 is best fit by a model of selective regime based upon differences in body size, whereas PC-2 and PC-3 are best fit by selective regimes based upon locomotor habit. Though differences in body size appear to have the greatest bearing upon the overall diversification of limb skeletal morphology in mustelids, locomotor habit remains an influential selective regime for the relative mass and proportions of the limb bones, as well as the moment arms of limb muscles.

LOC1-4  10:15 am  Variation of the felid (Mammalia: Felidae) scapula and implications for felid biology. Jasinski S.E.*, University of Pennsylvania; Dodson P., University of Pennsylvania
Abstract: The forelimb of felids is vital for understanding how these carnivorans move and capture prey. In turn, felid forelimbs are important for understanding the biology of these hypercarnivores. The scapula is pivotal in the anatomy of the forelimb as it is a key area of attachment for both extrinsic and intrinsic muscles. While cats are considered conservative in their bodyplans, differences are present in the morphology of the scapula and the corresponding forelimb myology. Although felids are generally similar, extant taxa fill different ecological niches, including cursoriality, piscivory, semi-arboreality, and scansoriality. Members of all major modern felid clades and predatory types were investigated. Eighty-five scapulae from 12 modern genera and 21 modern species of felids were utilized. Some features of the felid scapula are common to the entire family (e.g., enlarged caudal angle for pronounced large m. teres major and enlarged supraglenoid tubercle for a pronounced and large m. biceps brachii). However, key areas for understanding differences within the family include differences in the morphology of the cranial border, and of the acromion and suprahamate processes. Based on several variables, maximum variation occurs in medium-sized felids. By using geometric morphometrics and investigating the principal component analyses, the region of highest variation is the suprahamate process. Laterally, most felid clades form distinct groups, although the Prionailurus clade tend to group with or near the Lynx clade. On the medial scapular surface, the cursorial Acinonyx is distinct from all other felids. Additionally, some felid clades show a high degree of variation on the medial surface (e.g., Leopardus and Lynx), with the majority of variation present around the scapular head and neck. The inclusion of fossil felids with the data set should allow for interpretations of their possible behavior, biomechanics, and paleobiology.

LOC1-5  10:30 am  Hand skeleton and wingtip shape in coraciiform and piciform birds. Hieronymus TL*, NEOMED
Abstract: Differences in avian wingtip shape have well-characterized relationships to flight performance, migratory behavior, and feeding ecology. Kingfishers, woodpeckers, and their kin (Coraciimorphae) display a broad range of wingtip shapes, as well as a range of flight behaviors (including intermittent flight and flexed-wing upstroke) that cannot, as of yet, be clearly identified as adaptive responses to flight performance demands. These taxa also possess an unusual suite of morphologies in the forelimb skeleton at sites of flight feather attachment and articulation. This study examines the relationships between feeding and migration ecology, forelimb musculoskeletal characters,and distal primary feather lengths. Initial exploration of these relationships was conducted using phylogenetic co-inertia analysis on matrices of feeding and migratory behaviors (13 binary characters) and musculoskeletal morphology (79 categorical characters) for 65 coraciimorph taxa. Co-inertia between ecological characters and musculoskeletal characters points to several hot-spots of morphological variation, most notably the joint surfaces and muscle attachments of the carpometacarpus and digits II – III. A more fine-grained co-inertia analysis using skeletal GM semi-landmarks and distal primary feather lengths for 26 coraciimorph taxa recovers links between rounded wingtips and an elongate carpometacarpal-ulnare articular surface, increased area for the origin of flexor digiti minimi, and the presence of a pronounced dentiform process of the carpometacarpus that guides the tendon of extensor digitorum communis. The skeletal variability seen in coraciimorph taxa highlights potential mechanical constraints on flight stroke kinematics in these taxa.

LOC1 -6  10:45 am  Is variation in vertebral spine morphology associated with variation in myomere morphology in the killifishes? Minicozzi M, Northern Arizona University; Gillespie S, Northern Arizona University; Gibb A*, Northern Arizona University
Abstract: In fishes, the axial musculature is characterized by W-shaped muscles termed myomeres. However, little is known about the evolutionary factors that influence axial muscle morphology or how morphology affects locomotor performance. Our goal is to quantify variation in axial morphology in the caudal peduncle and, ultimately, determine how morphology influences locomotion in the killifishes (Cyprinodontiformes). We begin by surveying peduncle anatomy in three killifish species to test the hypothesis that muscle morphology and vertebral spine morphology co-vary. We predicted that if neural/hemal spines form a shallow angle relative to the vertebral column in a given species, then the myomeres would also inscribe shallow angles and form a compressed W shape; alternately, vertebral spine and myomere angles could demonstrate distinct patterns. Alizarin-red-stained and partially-cleared specimens of Gambusia affinis, Poecilia mexicana, and Kryptolebias marmoratus were dissected to expose myomeres in the peduncle. We quantified myomere and vertebral spine morphology (angles and lengths) to test the hypothesis that these two morphological parameters co-vary across species. We found that myomere morphology does vary significantly across species, and this variation is associated with parallel variation in spine angle: in species where the neural and hemal spines are more “sloped” toward the posterior vertebral centra to form a shallow angle, the anterior and posterior cones also form shallow angles, both relative to the vertebral column and to one another. In addition, when muscle length is normalized to body size, species with “deeper” (dorso-ventrally larger) caudal peduncles are formed by longer myomeres. Because vertebral elements and axial musculature are both derived from somites, these elements may be linked developmentally; however, the functional consequence of variation in peduncle depth and muscle/spine orientation remains unclear.

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