Size matters: Sexual dimorphism in the pelvic spurs of the Bahamian Boa ( Chilabothrus strigilatus strigilatus )

Determining gender in snakes almost always involves highly intrusive techniques that have the potential to seriously harm the animal. Clear morphological differences of conspecific males and females, defined as sexual dimorphism, can provide an alternative strategy to determine the sex of a snake with little harm. The commonly used sexual size dimorphism (SSD), however, is not ubiquitously applicable and has its limitations for some taxa and different life stages. The size differences in pelvic spurs, a little investigated morphological feature in some snakes, could provide a minimally invasive method to determine sex in these snakes. We compared the pelvic spurs of 32 Bahamian Boas of different life stages and body sizes to find out if pelvic spurs provide a robust alternative to identify sex in these snakes. We found that male Bahamian Boas possessed spurs nearly twice as long and notably more curved than females and that the proportion of the spurs to body size differed significantly between the sexes. Furthermore, spur length increased considerably more with an increase in body size in males than in females. We conclude that the investigation of the pelvic spurs in these boas allows for a simple and minimally invasive approach to determine gender and may also represent an alternative strategy for other species.