Sexual Dimorphism and Feeding Ecology of the Black-bellied Bunchgrass Lizard Sceloporus aeneus (Squamata: Phrynosomatidae) in Central Mexico

Morphology and resource use have a significant influence on lizard population dynamics. In this study, sexual dimorphism and feeding ecology were assessed in a population of Sceloporus aeneus from central Mexico. Sexual dimorphism was recorded, with males being larger than females in several morphological characteristics, such as jaw width, femur length, tibia length, and forearm length, but not snout-vent length (SVL) or jaw length, which were similar in both sexes. The stomach contents analysis indicated an insectivorous diet composed of 11 prey categories, of which females consumed 11 and males consumed 9. Low values of feeding niche breadth were found, as well as high overlap between sexes and seasons. For the whole population, adult preys of the family Formicidae and orders Coleoptera and Hemiptera showed the highest values of food importance and abundance. A higher volume of stomach contents was recorded during the dry season than the wet season in both females and males. Results showed a pattern of sexual dimorphism similar to that of other species of the genus Sceloporus, but different from those of other populations of the same species. Morphological variation in jaw length and width seems to be related to food resources use because, in spite of the high similarity in the diet between sexes, the volume of stomach contents was not correlated with SVL in females. These findings suggest a constant consumption of food that is subsequently invested in reproduction. Further studies analyzing morphology and diet and their effect on reproductive characteristics such as clutch size, eggs mass, and volume are needed among populations of this species. The results obtained in this research could help explain the differences and similarities previously reported on the morphology and reproductive characteristics for S. aeneus and other species of the S. scalaris group.