PETERSON, C.C.*; HUSAK, J.: Sexual selection and dimorphism of morphology and locomotor performance I n a polygynous, territorial lizard lizard

Integrative, whole-animal traits such as locomotor performance could, in theory, evolve via sexual selection. Predictions of this hypothesis include: 1) such a secondary sexual performance characteristic should be sexually dimorphic in adults, but not in juveniles, 2) proximate morphological correlates of performance should vary similarly, and 3) variation in performance among males should be correlated to mating success. We tested these predictions in a population of the polygynous, male-territorial lizard Crotaphytus collaris. Maximal sprint performance was measured on a computer-timed racetrack in complete ontogenetic series of wild-caught male and female collared lizards. Individual variation in sprint speed was highly repeatable. Sprint speed scaled to body size, but was not consistently correlated with any other morphological characteristics once body size was accounted for. Contrary to our prediction, size-relative sprint speed did not differ between sexes in any size class. In contrast, adult lizards (but not juveniles) were strongly sexually dimorphic for several morphological characteristics, including relative hindlimb length (a common intraspecific correlate of sprint speed in other lizards). We suggest that the longer legs of males may compensate for the slowing effect of their relatively much larger heads. In a subset of adult males for which both field and laboratory data were available, sprint speed was a better predictor of territory size and number of female home ranges overlapped than was body size or any other morphological variable. These results are suggestive of sexual selection for whole-animal locomotor performance in male collared lizards, but do not reveal proximate correlates of performance variation.