Sexual size monomorphism of a Pygmy Rattlesnake (Sistrurus miliarius) population in southwestern Missouri, USA

Pitvipers are known for their sexual dimorphism in their body size with males being larger than females. One hypothesis for the increased size of males is the selective pressure from ritualistic combat between males within a species. The Pygmy Rattlesnake (Sistrurus miliarius) is a diminutive species that has not seen a lot of research outside of central Florida. This study aimed to see if a southwestern Missouri population of S. miliarius follows the typical sexual dimorphism found in pitvipers. 48 S. miliarius were captured and 27 adults were compared based on the ratios of their tail length (TL) and mass, to snout-vent length (SVL). Males had longer TL:SVL than females but were no different in their body size. Like the central Florida populations, this Missouri population doesn’t show any sexual size dimorphism. We discuss the potential implications of these findings in the context of future research and other pitviper species.