Ecological and evolutionary significance of locomotor performance in collared lizards (Crotaphytus collaris)

Abstract

Scope and Method of Study: The purpose of this study was to test hypotheses concerning the evolution of locomotor performance in collared lizards (Crotaphytus collaris). I investigated the roles of natural and sexual selection on locomotor performance in collared lizards 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. In addition I examined how well performance, morphology, and steroid hormone levels predicted survival and mating success in different age and sex classes.

Findings and Conclusions: Sprint speed predicted survival only in hatchlings, not adults. 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 and hatchlings, intra-sexual selection for territory maintenance may be a stronger selective agent on males. To further support the latter hypothesis, I found that only maximal sprint speed predicted mating success. These results represent the first connection of morphology, performance, behavior, and fitness for a population of animals, and suggest that sexual selection may act on whole-animal performance traits.