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Session Schedule & Abstracts

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Sunday 3rd July, 2016

Symposium: Functional (secondary) adaptation to an aquatic life in vertebrates 3

Room: Salon A   2:30 pm–3:30 pm

Moderator(s): A. Houssaye & F. Fish
AQU3-1  2:30 pm  How to become aquatic with the mustelid toolkit? A morphometric insight into aquatic mustelid long bone evolution. Botton-Divet L*, UMR 7179 MNHN/CNRS, Mecadev, Paris; Fabre A-C, UMR 7179 MNHN/CNRS, Mecadev, Paris; Herrel A, UMR 7179 MNHN/CNRS, Mecadev, Paris; Cornette R, UMR 7205 MNHN/CNRS/UPMC/EPHE, ISYEB, Paris; Houssaye A, UMR 7179 MNHN/CNRS, Mecadev, Paris   
Abstract: The locomotor apparatus at least partially reflects where and how an animal moves. Biological structures are shaped by functional demands, yet are constrained by phylogenetic history as well as architectural and developmental constraints. As the locomotor apparatus can be used for locomotion through media with different mechanical properties, it is exposed to often diverging selective pressures. This is especially the case for semi-aquatic species that have to cope with the dramatic differences in density and viscosity in water versus land. Mustelids (Carnivora) display a large range of locomotor behaviors with several specializations ranging from arboreal to semi-aquatic. Semi-aquatic mustelids including otters (Lutrinae) and minks (Mustelinae) present many degrees of adaptation to the aquatic environment. This diversity is associated with a diversity in the modes of swimming that can involve one or both limb pairs. Moreover, the axial skeleton and tail may be used for propulsion too depending on the species and swimming speed. Here we examine the adaptations of semi-aquatic mustelids to locomotion in both environments and test whether minks present traits that are convergent on those observed in otters. To do so we use 3D geometric morphometrics to describe the shape of the long bones of both the fore- and hind limbs in five species of otters, two species of mink and closely related terrestrial Mustelinae. We test for convergence between minks and otters in long bone shape and explore whether swimming mode impacts long bone shape in otters.

AQU3-2  3:00 pm  Secondary evolution of aquatic propulsion in higher vertebrates: Validation and prospect. Fish F E*, West Chester University
Abstract: Re-invasion of the aquatic environment by terrestrial vertebrates resulted in the evolution of species expressing a suite of adaptations for high performance swimming. Examination of swimming by secondarily aquatic vertebrates provides opportunities to understand potential selection pressures and mechanical constraints, which may have directed the evolution of these aquatic species. Mammals and birds realigned the body and limbs for cursorial movements and flight, respectively, from the primitive tetrapod configuration. This realignment produced multiple solutions for aquatic specializations and swimming modes. Initially in the evolution of aquatic mammals and birds, swimming was accomplished by using paired appendages in a low efficiency, drag-based paddling mode. This mode of swimming arose from the modification of neuromotor patterns, associated with gaits characteristic of terrestrial and aerial locomotion. The evolution of advanced swimming modes occurred in concert with changes in buoyancy control for submerged swimming, and a need for increased aquatic performance. Aquatic mammals evolved three specialized lift-based modes of swimming that included caudal oscillation, pectoral oscillation, and pelvic oscillation. Based on modern analogs, a biomechanical model was developed to explain the evolution of the specialized aquatic mammals and their transitional forms. Subsequently, fossil aquatic mammals were described that validated much of the model. However for birds, which were adapted for aerial flight, fossil evidence has been less forthcoming to explain the transition to aquatic capabilities. A biomechanical model is proposed for birds to describe the evolution of specialized lift-based foot and wing swimming. For both birds and mammals, convergence in morphology and propulsive mechanics is dictated by the need to increase speed, reduce drag, improve thrust output, enhance efficiency and control maneuverability in the aquatic environment.

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