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Session Schedule & Abstracts

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Thursday 30th June, 2016

General Morphology 4

Room: Salon C   4:30 pm–5:45 pm

Moderator(s): Cuff AR, Higashiyama H
GEN4-1  4:30 pm  Ventilatory rib kinematics in the savannah monitor, Varanus exanthematicus: an XROMM study. Cieri RL*, University of Utah; Moritz S, Brown University; Brainerd EL, Brown University
Abstract: Squamates use aspiration breathing, driving air into their lungs mainly by using costal expansion to generate negative internal pressures. Because squamates use lateral undulations to locomote, rib motions are thus responsible for both ventilation and locomotion in these animals. The vertebral ribs are single headed, permitting three degrees of rotation between the ribs and vertebral column. In this study, X-ray Reconstruction of Moving Morphology (XROMM) was used to quantify the three dimensional rib rotations in 3 individuals of Varanus exanthematicus, which are typically described as bucket-handle rotation about a dorsoventral axis, pump-handle rotation about a mediolateral axis, and caliper motion about a rostrocaudal axis. During deep breathing in standing and prone lizards, we found rib motion to include a mixture of bucket and pump handle motions. Although the vertebral ribs did not deform during ventilation or translate substantially relative to the sternal ribs, a thin segment of the sternal ribs deformed during each breath. Compared to standing breaths, the sternum and vertebral column move around a more acute angle during prone breaths, and the vertebral ribs exhibit a greater degree of bucket handle rotation in prone breaths compared to standing. These differences in kinematics between breaths during different postures may help to explain the evolution of unrestrictive costal joint anatomies in Squamata, as the joint design must permit variations in ventilatory and locomotor motions under different conditions and postures. We found most of the ribs of V. exanthematicus to move during ventilation, unlike in iguanas. This difference in ventilatory strategy may reflect differences in endurance, locomotor strategies, or lung designs between Iguana and Varanus.

GEN4-2  4:45 pm  Grow bigger, dig deeper? Allometric effects of size on forelimb muscle architecture in the southern brown bandicoot (Isoodon obesulus; Marsupialia: Peramelidae). Lane M. L.*, Murdoch University; Warburton N. M., Murdoch University; Fleming P. A., Murdoch University
Abstract: Physiological cross-sectional area (PCSA), which is proportional measure of the maximum force-generating capacity of a muscle, is often used in studies of animal ecomorphology. In such studies, sample sizes is minimal and intraspecific variation is rarely considered, although is important where either potential ecological function changes with age, or where sexual dimorphism is correlated with behavioural differences or some degree of niche separation between the sexes. The southern brown bandicoot (Isoodon obesulus) is a medium-sized, omnivorous scratch-digging marsupial that utilises subterranean food items. Males (0.89kg) are significantly heavier than females (0.62kg). Isoodon obesulus fusciventer is commonly found across Western Australia, and reasonable numbers of ethically-sourced specimens are available, enabling a comprehensive comparison of the morphology of both sexes. We investigated intraspecific variation in forelimb muscle architecture during growth (for individuals ranging in body mass from 0.2-2kg). Larger animals (heavier than 1kg) have increased PCSA scores in 78% of muscles measured, with the extrinsic muscles, m. triceps brachii, muscles on the scapula and the m. flexor digitorum produndus muscles having the highest PCSA scores. Larger animals had greater investment in muscles involved in elbow extension, carpal flexion and digit flexion, while smaller animals had increased muscles involved in humeral retraction – the muscle actions emphasised in fossorial mammals where they generate large out-forces to act against the soil during fossorial behaviour. The intraspecific variations suggests likely differences in feeding ecology between animals of different sizes.

GEN4-3  5:00 pm  Big cat, weak cat? The scaling of postcranial myology within Felidae. Cuff AR*, UCL; Randau M, UCL; Pierce SE, Harvard University; Hutchinson JR, Royal Veterinary College; Goswami A, UCL
Abstract: Felids (cats) span a wide range of body masses, from around 1kg in the smallest extant species around 500kg in the largest extinct species. Across this range of sizes, they remain remarkably conservative with regards to the maintenance of a crouched posture, despite major biomechanical tradeoffs for the largest felids. Understanding the scaling of the locomotor musculature is important to see if and how felids compensate for their postural limitations. Using dissection, we collected data for vertebral and limb muscle architecture from nine species of felids spanning from 1.1kg to 133kg covering a wide range of extant body sizes. Data from the forelimbs show that many of the muscles involved in support functions scale with positive allometry, as do muscles linked to claw protraction and forearm flexion involved in the tackling of larger prey by the biggest felid species. In the hindlimb, only a few muscle metrics scale with positive allometry, and of those most are linked to hip and thigh movements. In the vertebral column, nearly all muscle metrics scale indistinguishably from isometry, despite there being osteological allometry across the vertebrae. When phylogeny is accounted for, nearly all significant allometries across the muscles of the postcranium become indistinguishable from isometry. Considering that cross-sectional area (a metric of force production) scales by mass2/3, and most muscles scale near-isometrically, unlike allometric trends that seem to apply to other mammals, the result is that large felids become relatively weaker than their smaller relatives. Using the scaling equations calculated from the modern species, and CT scans of fairly complete specimens for both the extinct North American lion (Panthera atrox) and the sabre-toothed cat Smilodon fatalis, we were able to reconstruct digital skeletons, and upon those the myology of these taxa, more accurately than previously possible.

GEN4-4  5:15 pm  Transforming tails into tools: syngnathid fishes used as bio-inspiration. Neutens C.*, Ghent University; De Dobbelaer B., KU Leuven; Claes P., KU Leuven; Praet T., Ghent University; Porter M., Clemson University; De Beule M., Ghent University; Christiaens J., Ghent University; De Kegel B., Ghent University; Dierick M., Ghent University; Boistel R., Université de Poitiers; Adriaens D., Ghent University
Abstract: The development and innovation of products can be compared to thousands of years of natural selection, where only those morphologies that had an adaptive advantage compared to others were retained. In our study, we have been looking for serially articulated systems that are characterized by an unlikely combination of strength, flexibility and the potential for miniaturization. A biological system that meets all these needs can be found in the tail of syngnathid fishes. Within this family, four different morphotypes can be distinguishes, being pipefishes, pipehorses, seahorses and seadragons. The natural variation among the tails of these different morphotypes goes from very solid and rigid system (as seen in pipefishes and seadragons) to very flexible, but less rigid systems (as seen in some pipehorses) but also systems that combine flexibility and rigidity (as seen in seahorses). The first part of this study focused on the different morphological patterns observed within and between the tails of the different morphotypes. For this part, virtual 3D reconstructions of complete tails were made based on µCT-scans. In the second part, a 3D surface based morphometric analysis was performed to determine the skeletal shape characteristics that can be linked to prehensile tailed species. In the third and last part, these characteristics were mimicked by using a virtual, dynamic model to determine what the implications are on the flexibility of the tail and which specific morphological adaptations could lead to the observed differences in tail flexibility and rigidity.

GEN4-5  5:30 pm  On the whole-anatomy of the murine hepatobiliary system by using the transparency method. Higashiyama H*, The University of Tokyo; Kanai Y, The University of Tokyo
Abstract: The biliary tract, including the gallbladder, is a well-branched ductal structure that exhibits great variation in morphology among vertebrates. Because of its variety, the biliary tract has been a major enigmatic body part in the field of comparative anatomy. However, the whole-anatomy of the biliary tract with related blood vessels, nerves, and smooth muscle has been not fully documented in many species especially in small animals, mostly because they surrounded by the opaque liver tissue. To reconcile this, at the outset, we described the whole-anatomy of the biliary system of mouse (Mus musculus) by the combination of the the classical technique of the color injection in blood vessel and biliary tract, immunohistochemistry, and recently invented transparency method CUBIC. Although some rodents have highly derived morphology, in the result, the topographical relationships of the murine biliary system were very similar to those of human, dogs and opossums. Phylogenetically, the murine hepatobiliary system should represent at least the ancestral state of eutherians, and is also useful as an experimental model for studying the human hepatobiliary system. We also report the recent advances in the comparative anatomy with transgenic mice, and other vertebrate species.

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