Meeting Abstract

73.4  Sunday, Jan. 6  Testing for temperature trade-offs in lizards ADOLPH, S.C*; BADGER, M.; Harvey Mudd College; Harvey Mudd College adolph@hmc.edu

Trade-offs in physiological performance between high and low temperatures are widely assumed to exist. However, temperature trade-offs in whole-organism traits have been surprisingly difficult to detect among individuals within populations. We tested for temperature trade-offs in (1) critical thermal limits and (2) sprint performance in Sceloporus lizards. In Sceloporus occidentalis, critical thermal maximum and critical thermal minimum were not positively correlated among individuals, as opposed to the prediction of the trade-off hypothesis. Instead, CTMin and CTMax exhibited a non-significant negative correlation. These results are consistent with two previous analyses that detected no significant evolutionary correlations between CTMin and CTMax among lizard species. In both Sceloporus occidentalis and S. graciosus, sprint performance was strongly positively correlated across temperatures, rather than exhibiting a trade-off. Correlations were similar in the two species. The magnitude of the phenotypic correlation between speeds at two different temperatures did not decline as a function of temperature difference. A quantitative genetic model suggests that these positive phenotypic correlations are unlikely to be accompanied by negative genetic correlations. The model suggests that selection on speed at a given temperature is more likely to result in evolution of overall speed rather than an evolutionary shift of the thermal performance curve along the temperature axis. Thus, we found no evidence of intraspecific temperature trade-offs in thermal tolerance or sprint locomotion in these lizards. CTMin, CTMax, and sprint speeds were all significantly repeatable, which is a requirement for detecting correlations (whether positive or negative). Repeatabilities were higher for sprint speeds than for critical thermal limits.