A central goal of evolutionary physiology is to understand adaptive significance of physiological plasticity in thermally variable environments. The primary objective of the proposed research is to evaluate whether phenotypic plasticity induced during embryonic development is adaptive for newt larvae. Unlike previous studies (1) the proposed project will focus on plasticity induced during embryonic development, (2) biologically realistic range of developmental temperatures will be used, (3) six competing hypotheses about plastic responses to developmental temperature will be tested simultaneously, and (4) a new vertebrate model will be used for physiological plasticity studies. Approximately 1000 of newt larvae will be used to fulfil primary research goals of the proposed research: (1) evaluate the effect of maternal oviposition site choice on the induction, direction, magnitude of developmental plasticity, (2) test multiple hypotheses of developmental plasticity response, and (3) test of adaptive significance of developmental plasticity under seminatural conditions. This research will considerably contribute to understanding of the adaptive significance of developmental plasticity and its role in the evolution of thermal physiology.