Growth Rates and Sexual Size Dimorphism in Bothrops jararacussu in Captivity (Viperidae, Crotalinae).

Abstract

Female-biased sexual size dimorphism (SSD) is the most widespread form of SSD in snakes and is often linked to increased female fecundity. Although the exact mechanisms underlying SSD development in snakes remain unclear, differences in growth rates between sexes are thought to be a primary driver. In this study, we tracked the growth rates of a litter of Bothrops jararacussu raised under a controlled environmental and feeding conditions. We compared the snout-vent length (SVL), mass, and specific growth rate indexes (L_SG and M_SG) between sexes over a 570-day period. At birth, both male and female snakes had the same SVL and mass, and their growth rates were similar during the first year. However, during the second year, male growth rates began to decline while female growth rates remained high, leading to the development of SSD. Notably, SSD emerged independently of food consumption and became statistically significant after males reached sexual maturation sizes. We suggest that the decrease in the male's growth rates was mediated by intrinsic factors, rather than energetic restriction. These findings contrast with those reported for male-biased SSD species and highlight the physiological strategies adopted by species evolving under different selective pressures.