Sexual differences in head form and diet in a population of Mexican Lance-headed Rattlesnakes, Crotalus polystictus

Sexual dimorphism of phenotypic traits associated with resource use is common in animals, and may result from niche divergence between sexes. Snakes have become widely used in studies of the ecological basis of sexual dimorphism because they are gape-limited predators and their head morphology is likely to be a direct indicator of the size and shape of prey consumed. We examined sexual dimorphism of body size and head morphology, and sexual differences in diet in a population of Mexican lance-headed rattlesnakes, Crotalus polystictus, from the State of México, Mexico. Maximum snout–vent length of males was greater than that of females by 21%. Males had relatively larger heads, and differed from females in head shape after removing effects of head size. In addition, male rattlesnakes showed positive allometry in head shape: head width was amplified while snout length was truncated with increased head size. In contrast, our data did not provide clear evidence of allometry in head shape of...