Intrapopulational variation in the skeleton of the desert spiny lizard, Sceloporus magister (Reptilia, Iguanidae)

Skeletal variation within a lizard population of Sceloporus magister is described and analyzed. Thirty-four osteological measurements were recorded on three age groups. A decrease in skeletal variation was found with increasing age. Of the three skeletal regions studied in each age group, the skull was the least variable, followed by the pectoral girdle-limbs and pelvic girdle-limbs regions. Skeletal variation between the sexes for adult and sub-adult age groups was also examined. Statistically significant sexual dimorphism was found only in the adult age group, with the adult females being less variable than the adult males in all three skeletal regions. This sexual dimorphism is analyzed in terms of three hypothesis: 1) competition hypothesis – which accounts for sexual dimorphism as a result of a balance between interspecific and intraspecific competition; 2) optimal feeding hypothesis – which relates sexual dimorphism to feeding strategy; and 3) sexual selection hypothesis – which relates sexual dimorphism to energy budgets involving growth, maintenance, and reproduction. Statistically significant sets of discriminating characters -which allow for the separation of the sexes were found for the adult and sub-adult age groups as well as for a combined age group. The significance of the discriminating characters along with their value in paleontological studies are discussed.