Adaptation or plasticity? Effects of temperature on metabolic rate and life-history traits in the Australian Painted Dragon lizard.

Daniel Jacob Ritchie, Christopher R. Friesen

The roles of adaptation and plasticity in shaping life-history traits have long been a subject of debate in evolutionary ecology, with the relevance of each varying by traits, populations, species, and clades. Ectothermic organisms, which obtain most of their metabolic energy from ambient heat, occupy wide geographic ranges where heat can be unevenly distributed. There is considerable potential for populations at opposite ends of a temperature cline to exhibit differing thermal adaptations, energy budgets, and phenotypically plastic responses to temperature. Using factorial laboratory experiments, we investigated the hypothesis that two populations of male painted dragon lizards (Ctenophorus pictus) would differ significantly in thermal physiological traits at opposite ends of a temperature-cline. After acclimatising both populations in warm and cool temperature treatments, we quantified differences in thermal performance curves, somatic growth (body size and weight) and reproductive investment (relative testes mass). We found that the Northern, warm-adapted population had a significantly higher metabolic rate at high temperatures and ina greater investment in body size and relative testes mass than the cool-adapted southern population, consistent with geographic variation of thermal traits across both populations. The effects of temperature treatment were negligible, except for body length (skeletal growth), which was greater in the cool treatment for both populations, suggesting similar thermal plasticity responses. Our results indicate that thermal adaptation and phenotypic plasticity both contribute to life-history variation in C. pictus.