Sexual dimorphism and ontogenetic changes of Amazonian pit vipers (Bothrops atrox)

Sexual dimorphism of body size (SSD) is widespread in snakes and has been the subject of numerous studies, but few have examined sexual shape dimorphism (SShD). The present study explores sexual size and shape dimorphism in the Amazonian pit viper Bothrops atrox. We combine linear and geometric morphometrics to describe differences in body size and head shape between the sexes and how these differences are generated throughout ontogeny. Our study shows that B. atrox is sexually dimorphic, with females being larger than males, except for tail length. Females also have relatively larger heads, differing not only in size but also in shape. Our results reveal that both size and shape of the head vary significantly from neonates to adults. Head shape changes in B. atrox are associated with allometry and follow similar trends in both sexes: neonates have a relatively shorter and more robust head and shorter snout, while adults show a wider and flattened head. Although our results indicate that allometry is an important factor in determining sexual shape dimorphism, additional studies on diet and performance may be necessary to understand the ecological implications of such differences.