HUSAK, J.F.*; Oklahoma State University: When Do Collared Lizards Use Maximal Sprint Speed?

In order to understand how selection acts on performance capacity, the ecological role of the performance parameter being measured must be determined. Knowing if and when an animal uses maximal performance capacity may give insight into what specific selective pressures may be acting upon morphology and performance. I investigated the potential roles of natural and sexual selection on locomotor performance in collared lizards (Crotaphytus collaris) by measuring maximal sprint speed in the laboratory, in addition to field-realized sprint speed for the same individuals in three different contexts: foraging, escaping a predator, and responding to a rival intruder. Of the three contexts, females used closer to maximal speed while escaping predators than in the other contexts. Adult males, on the other hand, used closer to maximal speed while responding to an unknown intruder tethered within their territory. Sprint speeds during foraging attempts were far below maximal capacity for all lizards. Collared lizards appeared to choose microhabitats near refugia such that maximal speed was not necessary to escape predators. Although natural selection for predator avoidance cannot be ruled out as a strong selective force acting on locomotor performance in collared lizards, especially in females, intra-sexual selection for territory maintenance may be a stronger selective agent on males.