Two populations of the Neotropical lancehead Bothrops leucurus were studied in two locations in Brazil (Espirito Santo, ES, and Bahia, BA) with different rainfall seasonality patterns. The timing of reproduction was very similar in both populations, with the mating season occurring in autumn (when spermatozoa were found in uteri) and births occurring in summer. In males, spermatogenesis peaked in autumn, with evidence for increased secretory activity in the epithelium of the ductus deferens during the mating season in both populations. Our results indicate that phylogenetic inertia plays a major role in determining the timing of reproductive events in B. leucurus. However, snout-vent length (SVL) and clutch size were larger in individuals from BA than ES, which may be a result of differences in rainfall seasonality or other proximate factors (e.g., differential prey availability).Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Univ Estadual Paulista, UNESP, Programa Posgrad Biol Anim, Sao Paulo, BrazilInst Butantan, Lab Ecol & Evolucao, Sao Paulo, BrazilUniv Fed Sao Paulo UNIFESP, Dept Expt Neurol, Sao Paulo, BrazilUniv Estadual Paulista, UNESP, Programa Posgrad Biol Anim, Sao Paulo, BrazilFAPESP: 08/56169-5FAPESP: 12/15037-4