Nineteen samples of Cnemidophorus tigris gracilis (119 clutches) and 11 samples of C. t. septentrionalis (127 clutches), covering latitudinal and elevational gradients of approximately 8.3? and 1669 m, were used to examine the relationship of clutch size with body size of reproductive females and elevation, latitude, and mean annual precipitation of collecting sites. Of the four independent variables, body size and elevation had significant linear relationships with clutch size. Reproductive females of C. t. septentrionalis have larger bodies and produce larger clutches, on average, than reproductive females of C. t. gracilis. The difference in clutch size remained significant when body size was held constant in an analysis of covariance, but became nonsignificant with elevation as the covariate. In general, C. t. gracilis occupies lower elevational habitats, while the range of C. t. septentrionalis includes higher ele- vations. The simultaneous presence of yolked ovarian follicles and oviductal eggs in two individuals from southern populations of C. t. septentrionalis suggests a retained potential to produce multiple clutches. We conclude that the production of one relatively large clutch per season in C. t. septentrionalis rather than several smaller clutches (sensu C. t. gracilis) represents a phenotypically plastic response to elevation (climatic regimen) rather than being genetically fixed in this taxon. Two different life-history strategies are found among populations of Cnemidophorus tigris in its extensive latitudinal range. For example, pop- ulations of C. t. gracilis, distributed south of 36? in western and southern Arizona and parts of western Sonora, Mexico, produce several rela- tively small clutches of eggs during the repro- ductive season (Pianka, 1970; Parker, 1972). In contrast, populations of C. t. septentrionalis oc- cupy a disjunct range north of 36? on the Col- orado Plateau and produce one relatively large