Low repeatability of preferred body temperature in four species of Cordylid lizards: Temporal variation and implications for adaptive significance
van Wyk, J.H.
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Preferred body temperatures (Tsel) of ectotherms are important for ecological and evolutionary studies. In lizards, the measurement of Tsel is controversial for several reasons, generally related to hypotheses addressing how Tsel may evolve in the wild. Although seldom explicitly tested, evolutionary hypotheses of adaptation to local climate require that Tsel meets the conditions of natural selection, which include repeatability, heritability and a link to fitness. Here, we investigated repeatability (τ, intra-class correlation coefficient) of Tsel at several time-scales using four Cordylid species from heterogeneous thermal habitats. Although there was significant inter-individual variation within days (P < 0.005 in most cases), there was no significant inter-individual variation when calculated across several days (P > 0.05). Repeatability was low in all species investigated (from 0 to 0.482) when compared against other estimates of repeatability of Tsel in the literature. Irrespective of how Tsel was calculated, it showed inconsistent and variable temporal effects across species. Furthermore, repeatability of Tsel did not change with acclimation to laboratory conditions. These data have implications for understanding the evolution of thermoregulation in these and other ectotherms.