The role of thermal environment in determining the life history of a terrestrial salamander

Largely using previously published data, we analyzed geographic variation in adult body size of terrestrial salamanders of the Plethodon glutinosus complex. Maximum body size of adult males is determined by size at maturity. In turn, size at maturity is determined by a negative relationship with environmental temperature. Moreover, both age at maturity and growth rate are correlated with size at maturity, but apparently only as coincidental correlates through the influence of temperature. The number of degree-days, estimated using temperature data from respective geographic locations, accurately predicts age at maturity for salamanders living in these areas. Development under cooler thermal regimes is more depressed than growth and, consequentially, adult body sizes are greater in cooler climates. This pattern of size variation fits thermal predictive models proposed for larval development in amphibians that breed in ponds. Phenotypic variation in adult body size appears to be accounted for largely by plastic responses to variation in thermal environments and may reflect a single reaction norm for the complex.