The biomechanics and energetics of locomotion in sea turtles: understanding the influence of load carrying on performance

Turtles have the most distinctive body plans of vertebrates (1). Turtles appear in the fossil record over 220 million years ago. Turtles are unique among vertebrates in that their whole body is enclosed within a rigid bony shell, composed of the carapace and plastron, that protects from predators. Their shells would appear to constrain their lives; however, turtles inhabit a range of both aquatic and terrestrial habitats and many species effectively move between both (2,3). We will integrate biological, biomechanical and physiological techniques to collate energetics data across three turtle species at the organismal down to the cellular level (4). We have selected sea turtles as they vary in their degree of specialisation to different loads(5) to provide a broad range that will allow us to better understand turtle locomotor performance, the trade-offs in changing environments and the impact of constraints on their life in a box. Studying turtles will provide an important model for future research on functional diversity, adaptation and evolution. Water and air represent the fluid media in which organism must survive and move and the physical disparities (density, viscosity, gravitational load) between these environments can have important consequences for adaptation and performance of organisms like turtles that routinely transverse between aquatic and terrestrial environments. There are key differences in substrate between these terrestrial biomes as well. We will determine how load bearing influences differences in the metabolic cost of transport and locomotor biomechanics at the organismal level and investigate using musculoskeletal computational models the adaptations that ultimately physiologically constrain locomotor performance in sea turtles in the context of environmental change.