Acute and Seasonal Effects of Temperature on Bite Performance of Alligator Snapping Turtles (Macrochelys temminckii)

Abstract

Environmental temperatures influence most aspects of ectotherm biology, especially when fluctuating on daily and seasonal scales. The Alligator Snapping Turtle (Macrochelys temminckii) is a species of conservation concern inhabiting temperate latitudes in the southeastern United States. To study the effect of temperature and season on the bite performance of M. temminckii, we used a force transducer and high-speed videography to measure bite force and kinematics, including bite duration, jaw velocity and acceleration, and lunge velocity and acceleration, for 21 captive subadult M. temminckii. We also recorded bite behaviors, including willingness to gape and bite, and pre-bite aggressive displays. We conducted trials at 5°C, 15°C, and 25°C, and repeated our measurements in summer and winter. Maximum bite force varied significantly with temperature, albeit not to an extent likely to be biologically relevant. All bite kinematics varied significantly across at least one of the testing temperatures within seasons, with individuals performing maximally at 25°C. Willingness to bite was more affected by temperature than willingness to gape, with subjects requiring more provocation to gape and bite at 5°C than at higher temperatures and displaying fewer pre-bite aggressive behaviors. There was limited evidence of seasonal acclimation in bite kinematics, with higher summer temperatures yielding maximal performance, and measurements at lower temperatures varying little between seasons. Our findings support the need for rigorous standardization of temperature in studies of ectotherm performance and suggest that care must be taken in selecting the time of year in which temperature studies are conducted.