Sprint speed and degree of wariness in two populations of whiptail lizards (Aspidoscelis tesselata) (Squamata Teiidae)

Predation is an important selective force that can influence morphology, physiology, behavior, and life-history traits in natural populations. Lizards exhibit a variety of antipredator strategies including flight. Laboratory studies were conducted to determine sprint speed at various body temperatures for juveniles from two populations of the unisexual whiptail lizard Aspidoscelis tesselata. Lizards reared from eggs collected at Terlingua Creek, TC (a site characterized by more abundant vegetation; Big Bend National Park, Texas) exhibited significantly slower sprint speeds regardless of body temperature (25, 30, or 35 oC), as compared to conspecifics from Hot Springs, HS (sparse vegetation). At 30 degrees C, maximal sprint speed of HS and TC lizards was 46.9 and 38.1 cm/sec, respectively. Field studies were also conducted to assess degree of wariness, Lizards from the HS site ran at a greater approach distance, ran to a greater final distance, and to a greater final total distance than their counterparts of similar size and mass from the TC site. From a total of 186 lizards that were approached at the HS site, 65 (35%) fled to an open area while 121 (65%) stopped running when they found a suitable shelter site under a rock or bush. Similarly, 37 of 92 lizards (40%) stopped running in an open area at the HS site, as -compared to 60% that found a shelter site, usually under a shrub or mesquite bush. These results suggest that population differences in sprint speed and wariness may have a genetic basis and result from selection favoring faster sprint speed in animals found in habitats that make them more vulnerable to predation.