Geographical, climatic and biological constraints on age at sexual maturity in amphibians

Age at sexual maturity is a central life-history parameter, strongly related to key traits such as body size and longevity. It is influenced by environmental and intrinsic factors that affect growth rates and gonad development. Using data on the age at sexual maturity in 123 species of amphibians worldwide, we tested whether sexual maturity is delayed at high altitudes and latitudes, in cold and dry regions and on islands. We further tested whether sexual maturity is delayed in species with parental care and direct development (no tadpole stage). Using phylogenetic regression and correcting for body size, we found a positive relationship between latitude and sexual maturity. Surprisingly, altitude was negatively correlated with sexual maturity in small species. Temperature was negatively related to sexual maturity in females but not in males. Precipitation and seasonality did not effect on either sex. Species that engage in parental care or have direct-developing larvae mature early. We found no effect of insularity, contradicting the insular syndrome hypothesis. Meta-analyses revealed that, within species, sexual maturity is reached at younger ages in warm temperatures in aseasonal environments and in low altitudes. Thus, although life-history strategies affect maturation time, climate can further delay or accelerate development – probably through effects on metabolic rates and season length.