Thermal dependence and individual variation in tonic immobility varies between sympatric amphibians.

Tonic immobility (TI) is an important antipredator response employed by prey in the last stages of a predation sequence. Evolution by natural selection assumes consistent individual variation (repeatability) in this trait. In ectotherms, which experience variable body temperatures, TI should be repeatable over a thermal gradient to be targeted by natural selection; however, information on thermal repeatability of this trait is missing. We examined thermal repeatability of TI in juveniles of two sympatric amphibians, smooth (Lissotriton vulgaris) and alpine (Ichthyosaura alpestris) newts. Both species showed disparate TI responses to body temperature variation (13-28 °C). While the proportion of TI response was repeatable in both taxa, it increased with body temperature in alpine newts but was temperature independent in smooth newts. Duration of TI decreased with body temperature in both taxa but was only repeatable in smooth newts. Our results suggest that a warming climate may affect population dynamics of sympatric ectotherms through asymmetry in thermal reaction norms for antipredator responses.

Repeatability and heritability of resting metabolic rate in a long-lived amphibian.

Resting metabolic rate (RMR), i.e. spent energy necessary to maintain basic life functions, is a basic component of energy budget in ectotherms. The evolution of RMR through natural selection rests on the premise of its non-zero repeatability and heritability, i.e. consistent variation within individual lifetimes and resemblance between parents and their offspring, respectively. Joint estimates of RMR repeatability and heritability are missing in ectotherms, however, which precludes estimations of the evolutionary potential of this trait. We examined RMR repeatability and heritability in a long-lived ectotherm, the alpine newt (Ichthyosaura alpestris). Individual RMR was repeatable over both six-month (0.28 ±â€¯0.09 [SE]) and five-year (0.16 ±â€¯0.07) periods. While there was no resemblance between parent and offspring RMR (0.21 ±â€¯0.34), the trait showed similarity among offspring within families (broad-sense heritability; 0.25 ±â€¯0.09). Similar repeatability and broad-sense heritability values in parental and offspring generations, respectively, and non-conclusive narrow-sense heritability suggest the contribution of non-additive genetic factors to total phenotypic variance in this trait. We conclude that RMR evolutionary trajectories are shaped by other processes than natural selection in this long-lived ectotherm.

Repeatability of thermal reaction norms for spontaneous locomotor activity in juvenile newts.

Locomotor activity is a major attribute of animals. Although this trait determines important ecological processes, such as dispersal and species interactions, the sources of its variation are not fully understood. We examined the influence of body temperature (13, 18, 23, and 28 °C) and individual identity on spontaneous locomotor activity in juvenile alpine newts, Ichthyosaura alpestris, over three consecutive weeks. Locomotor activity was characterized by four parameters: distance covered, mean velocity, frequency of movements, and total activity rate (all directional and non-directional movements). Apart from total activity rate, thermal reaction norms for locomotor parameters had convex or concave curvilinear shapes. During the first trial series, i.e. across the four body temperatures that were tested, individual identity explained less variation in thermal reaction norms than during the second series. Individual means, i.e. the vertical positions of individual thermal reaction norms, were repeatable between trial series in all locomotor activity parameters but the frequency of movements. We conclude that spontaneous locomotor activity is a complex trait, which can be characterized by several parameters with varying individual repeatability and thermal dependency. This information should be considered for planning further locomotor activity experiments, conservation strategies, and modeling ectotherm responses to climate change.