Geographic Differences of Growth Rate of Sceloporus Lizards (Sauria: Iguanidae)

Laboratory produced hatchlings of Sceloporus graciosus graciosus, S. undulatus consobrinus, S. u. garmani and S. u. undulatus that were raised under identical social, thermal-gradient and feeding environments grew at significantly distinct, population-specific rates. Growth rates expressed in the laboratory closely approximated those measured in the field for some populations, but were higher in the laboratory for others. Juvenile growth rate differences measured in the field seem due in part to genetic differences and in part to differences in the quality of the natural growing environment. T HE field studies of Tinkle (1967), Tinkle and Ballinger (1972) and others have pointed out that geographic variation of lifehistory parameters exists in lizards. At least two important questions, germane to the study of any trait differences, remain. First, what kinds of genotypic-environmental interactions result in these differences? Second, if there is some degree of genetic determination of these differences, how have environmental pressures selected for the evolution of differences?