1) Phenotypic variation within populations is influenced by the environment via plasticity and natural selection. How phenotypes respond to the environment can vary among traits, populations, and life stages in ways that can influence fitness.

2) Plastic responses during early development are particularly important because they can affect components of fitness throughout an individual’s life. Consequently, how natural selection shapes developmental plasticity could be influenced by fitness consequences across different life stages. Moreover, spatial variation in selection pressures could generate differences in plastic responses among populations.

3) To gain insight into sources of variation in phenotypes and survival, we used a laboratory egg incubation experiment using brown anole lizards (Anolis sagrei) from mainland (ancestral) and island (descendent) populations, combined with a mark-release-recapture experiment in the field. Our study was designed to (i) quantify the effects developmental temperature on embryo development and offspring morphology, (ii) assess how developmental temperature influences offspring survival across different life stages, and (iii) quantify how thermal reaction norms vary among ancestral and descendant populations.

4) Developmental temperature influenced offspring morphology, but thermal reaction norms of embryos showed little variation among populations. Developmental temperature influenced offspring survival, but the patterns differed between embryo and hatchling stages; the optimal temperature for embryos was about 5ºC lower than that for hatchlings. High temperatures were thermally stressful to embryos, but they reduced incubation duration and led to early hatching. In turn, earlier hatching increased the probability of survival to adulthood. Moreover, the effect of temperature on hatchling survival was most pronounced for offspring that hatched late in the season.

5) The difference in optimal developmental temperatures between life stages may be driven by physiological tolerance for embryos and by ecological factors for hatchlings. Moreover, the fitness consequences of the developmental environment depend upon the phenology of hatching. Overall, these results highlight how the developmental environment can differentially effect fitness across life stages and show that temporal thermal heterogeneity can influence survival of embryos, but the consequences on post-hatching stages may vary at different times of the season.