Thermal acclimation of swimming performance in newt larvae: the influence of diel temperature fluctuations during embryogenesis

P> Thermal acclimation is one of the basic strategies by which organisms cope with thermal heterogeneity of the environment. Under predictable variation in environmental temperatures, theory predicts that selection favours acclimation of thermal performance curves over fixed phenotypes. We examined the influence of diel fluctuations in developmental temperatures on the thermal sensitivity of the maximal swimming capacity in larvae of the alpine newt, Triturus alpestris. We incubated newt eggs under three thermal regimes with varying daily amplitudes (1, 5 and 9 degrees C) and similar means (17 center dot 6-17 center dot 9 degrees C), and accordingly we measured the swimming speed of hatched larvae at three experimental temperatures (12, 17 and 22 degrees C), which they would normally experience in their natural habitat. Embryonic development under low and middle temperature fluctuations produced larvae with similar swimming speeds across experimental temperatures. In contrast, the most fluctuating regime induced development of phenotypes, which at 12 degrees C swam faster than larvae developed under moderate diel fluctuations. Our results provide evidence that diel temperature fluctuations induce acclimation of thermal dependence of locomotor performance. In ectotherms experiencing diel cycles in environmental temperatures, this plastic response may act as an important pacemaker in the evolution of thermal sensitivity.