Reproductive seasonality is common among snakes, with mating, pregnancy, and birth or oviposition occurring only during few months of the year and modulated mainly by two environmental phenomena—temperature and rainfall. Species of Bothrops inhabit regions with varied climatic conditions, including those that are tropical, subtropical, equatorial, and semiarid. Bothrops atrox is an endemic and widespread species of the Amazon rain forest. Such habitat is characterized by an equatorial climate with little variability in temperature and humidity, but marked seasonality in intense precipitation. We investigated several aspects of the reproductive biology of B. atrox, including the reproductive cycle, the sexual segment of the kidney (SSK), sperm storage, and the possible influence of temperature and rainfall on pregnancy duration, birth, and spermatogenesis. Specifically, we examined museum specimens to describe sexual dimorphism, litter size, and male and female urogenital cycles through macroscopic and histological analyses. Females of B. atrox exhibited follicular recrudescence mainly from January to April (part of the wet season). Pregnant females were found throughout the year (except May), but births were found to occur mainly at the end of the dry season (August–October). Males exhibited SSK hypertrophy and sperm production in the wet season (November–April). Females were found to be larger than males, but males of B. atrox—as with other members of the B. atrox species complex—obtain relatively larger body sizes when compared with other species of Bothrops, which might be an adaptive response to male–male combat in this species. Together, our results show that B. atrox from Amazonia has a unique reproductive strategy (for each sex) among pit vipers, indicating greater reproductive plasticity when compared with its congeners.
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Vol. 75 • No. 3