Meeting Abstract

S5-4   10:30 - 11:00  Diving birds are different beasts: Morphology and evolution of aquatic Aves Lapsansky, AB*; Warrick, DR; Tobalske, BW; University of British Columbia; Oregon State University; University of Montana tony.lapsansky@gmail.com

Diving poses significant challenges to terrestrial animals, yet members of all major quadrupedal lineages have re-invaded water to some extent. From the inception of evolutionary theory, study of these lineages has deepened our understanding of the underlying principles of evolution, adaptation, and constraint. Still, there is much to be learned. Gaps in our knowledge exist in part because much of the research on diving animals has focused on mammals. But with over 200 diving species from 16 orders, birds represent a widespread yet poorly studied air-water invasion. Birds and mammals are different beasts. In aquatic birds, adaptations for diving have been superimposed on a Bauplan adept at fluid locomotion: streamlined bodies to reduce drag and forelimbs capable of producing thrust from a non-solid substrate. Thus, insights gained from studying diving mammals may not translate directly to birds, as the tradeoffs between life in air and life in water may be of lesser import. We performed an exhaustive review of the locomotor strategies of diving birds and used new and previously published data to test fundamental hypotheses seeking to explain their morphology, behavior, and evolution. Contrary to the prevailing hypotheses, we find that diving in birds did not co-evolve with the enlargement of muscles used during aquatic locomotion - that is, diving birds are not “weighed-down” by muscular specializations for water, which would limit their ability to locomote in air. Furthermore, we find no evidence that wing-propelled diving has selected for small wings due to hydrodynamic drag. Excluding flightless birds, both wing-propelled and foot-propelled divers have equally small wings for their body sizes, likely driven by selection against buoyancy. Our results and the diversity of diving birds highlight the importance of exaptation and innovation in the evolution of organismal form and function.