Meeting Abstract
Elevational clines have long been recognized for their consistent patterns of climatic variation. Specifically, daily temperatures at lower elevations are generally warmer and less variable than daily temperatures at higher elevations. Thus, organisms at either extreme of the elevational range are likely experiencing markedly different climates. The consistent thermal differences that occur with elevation are likely to drive local adaptation to the thermal regimes frequently experienced. Here, we compared the thermal physiology of three sympatric phrynosomatid lizard species (Sceloporus tristichus, S. graciosus, and Uta stansburiana) across an elevational gradient in San Juan County, Utah. Because climate varies with elevation, we predicted lower thermal tolerance would decrease as elevation increased, and that critical thermal breadth would increase with elevation as daily temperatures become more variable with increasing elevation. We also expected lizards at lower elevations to exhibit greater thermal specialization at lower elevations (i.e., higher maximal performance across a narrower range of body temperatures). Contrary to predictions, we found no evidence of consistent patterns of variation in thermal physiology across elevation in any of the three lizard species we measured. Although lizards were captured across their entire elevational range for the area, the gradient (~500m for each species) may not have provided a large enough thermal gradient to drive adaptive processes. Alternatively, the seeming ubiquity of each of these species along the elevation gradient and lack of discernible patterns in thermal physiology may suggest a relatively large degree of gene flow along the gradient, potentially washing out any local adaptation at the extremes.
