Cusack, B.J.*; Niewiarowski, P.H.: Variation In Endurance In The Fence Lizard, Sceloporus undulatus: The Effect Of Temperature, Behavior, And Morphology

We measured the thermal sensitivity of endurance capacity, preferred body temperatures, activity body temperatures, and several morphological characteristics of Sceloporus undulatus from Nebraska and Ohio. Overall, S. undulatus from Nebraska had higher endurance than Ohio S. undulatus. Endurance measured over S. undulatus‘ range of field active body temperatures was statistically insensitive to temperature. Optimal body temperature for performance was statistically higher for the Nebraska population (mean = 31.26 C versus 29.86 C). Preferred body temperatures of both populations ranged approximately 29-34 C with a mean of 31.5 � 0.1 C. There was no difference between populations in the relationship between optimal body temperatures and preferred body temperatures. There was also no difference between populations in activity body temperatures (NE mean = 33.7 C; OH mean = 33.3 C). A previous study (Balk and Niewiarowski, 1998) found that S. undulatus from NE had lower maximal sprint speeds than S. undulatus from OH. Endurance and maximal sprint speed therefore appear to tradeoff at the population level between NE and OH. Furthermore, adult lizards from NE (high endurance, low maximal sprint speed) experience higher rates of mortality than adult lizards from OH (low endurance, high maximal sprint speed). This pattern is consistent with the hypothesis that endurance may be more important than maximal sprint speed in escaping predators, however there is currently no direct evidence to support such an hypothesis. More studies are needed to investigate covariation between locomotor performance parameters, life history traits and geographic variation in this species.