Newswise — It’s hard to be two things at once. But people aren’t the only ones with this problem - animals face it too. In many cases, the reason is what biologists call “tradeoffs”: being good at one task may mean having traits that get in the way of accomplishing others. Tradeoffs are especially common in the different ways that animals move. For example, just like boats, swimming animals can have a hard time being both stable (resisting being knocked off course) and maneuverable (turning and navigating around obstacles). Many fishes have flexible bodies that help them succeed in both jobs, but many animals have more rigid bodies like boats. Animals with rigid bodies like boats should be more stable than maneuverable, but have had less study. Are there ways that such animals can break the mold and avoid tradeoffs?

Christopher Mayerl and colleagues examined this question by comparing swimming stability and turning in two different species of aquatic turtles with rigid bodies: the painted turtle, Chrysemys picta, and the pink-bellied sideneck turtle, Emydura subglobosa.  Their first step was to train turtles to chase worms that were pulled through a mechanical maze. Once this was done, they filmed the turtles using high-speed video and measured how stable they were and how good they were at turning.

Mayerl and colleagues found that the sideneck turtle was both more stable, and better at turning, than the painted turtle. The keys to how it avoided the tradeoff they expected involved differences in both body shape and behavior between the species. Sidenecks had larger hands and feet than the painted turtle, improving their ability to produce forces in water. Sideneck turtles also used faster limb movements during turning, and moved their limbs through smaller arcs during stability trials, helping to improve performance in both tasks. These results highlight how the structure and behavior of animals interact to determine how they perform in the environment. In addition, finding that rigid animals also have ways to avoid tradeoffs between stability and maneuverability could help aid designs of rigid vehicles made by humans.