The relationship between bite force, sprint speed, and temperature in female Sceloporus occidentalis lizards
Authors:Yesenia Ibarra, Kristopher B. Karsten
Mentor:Kristopher B. Karsten , Assistant Professor of Biology, California Lutheran University
The purposes of this study were to determine if 1) there is a relationship between temperature and bite force and 2) if there is a trade-off between bite force and sprint speed in female Sceloporus occidentalis lizards. Lizards depend on the environment to regulate their body temperature. For example, S. occidentalis often regulate their body temperature to about 35°C, a temperature at which sprint performance is at a maximum. Bite force is important for lizards in eating prey and defending themselves from predators or rival lizards. Environmental temperature differences may impact this ecological variable. We propose that the female bite performance will have a lower curve, but will exhibit relatively high performance across a wide range of temperatures. However, one trade-off for having stronger bite force (i.e., larger heads) is that the larger head may inhibit maximal sprint speed (ability to escape a predator) for a given body size. We measured bite force in 18 females across 9 different temperatures ranging from 15-38°C. We incubated lizards for 1 hour at each of the test temperatures. After incubation, each lizard bit the force transducer 3 times per trial. Then, we placed lizards in an incubator at 35°C for 30 minutes of recovery. After collecting bite forces, we incubated lizards at 35°C for 1 hour and sprinted them on a racetrack with sensors located 25 cm apart. Each lizard sprinted 3 times with 1 hour rest between trials. We measured morphology after the sprint trials. Temperature did not have an effect on bite force performances in female lizards; females had relatively high performance across all temperatures. Additionally, we found no trade-off between bite force and sprint speed. Having a larger head (and bite force) does not negatively impact sprint performance.