Influence of interspecific competitors on behavioral thermoregulation: developmental or acute plasticity?

Abstract

Many ectotherms reduce their exposure to changing thermal conditions using behavioral thermoregulation. The effectiveness of behavioral thermoregulation in maintaining ectotherm body temperatures within the target range is influenced not only by environmental (operative) temperatures but also by the presence of other con- and heterospecific individuals. How species’ interactions affect behavioral thermoregulation is largely unknown. Theory predicts that species’ interactions could affect the plasticity of behavioral thermoregulation in two ways, i.e., by developmental plasticity of a preferred temperature range or by an acute shift in body temperatures. Empirical tests of these predictions are scarce. We examined the developmental and acute effects of heterospecific social interactions on the accuracy and effectiveness of thermoregulation in the larvae of two competing species, Ichthyosaura alpestris and Lissotriton vulgaris. The presence of heterospecifics during larval development had no effect on preferred body temperatures but it modified later acute thermoregulatory responses to heterospecifics. Ichthyosaura alpestris larvae from heterospecific tanks increased their thermoregulatory accuracy and effectiveness, while L. vulgaris larvae from conspecific tanks relaxed their thermoregulatory efforts. The thermal dependence of somatic growth suggests that modified behavioral thermoregulation has the potential to accelerate growth in competitively dominant I. alpestris. Acute thermoregulatory responses are affected by heterospecific social interactions in newt larvae, but not conspecific. A developmental plastic response modified body temperatures not the target thermoregulatory range, which shows that the influence of heterospecific social interactions is more complex than predicted by theory. Species interactions complicate estimating an ectotherm’s vulnerability to ongoing climate change. Many ectothermic animals control their body temperature through behavioral thermoregulation. Their thermoregulatory decisions are influenced not only by environmental temperatures, but also by the presence of other species. We show that the current thermoregulatory effort in interacting newt larvae is affected by previous experience with competing species. The influence of heterospecific social interactions is more complex than predicted by theory, which complicates estimating an ectotherm’s vulnerability to ongoing climate change.