Lizard Reproductive Effort: Caloric Estimates and Comments on Its Evolution

Abstract

The energy content of eggs of 10 lizard species was determined and used as a measure of reproductive effort (ratio of clutch calories to body calories). Values for eggs ranged from 5.87 to 7.20 cal/mg ash—free dry weight (°=6.37). Species differences in calories going into reproduction during a breeding season, however, were primarily due to differences in clutch size and clutch frequency between species. Correlation analysis between three measures of reproductive effort, including the preceding, and a suite of demographic variables revealed only one significant correlation (negative) between clutch calories to body calories ratio and mean annual adult survivorship. The energy allocated to eggs in comparison to total annual energy expenditure was estimated for three of the species investigated. Sceloporus graciosus had the highest reproductive effort, with proportional values for first and older breeders about the same. The proportion of total energy expended on reproduction was slightly lower for UTA stansburiana, with first and older breeders exhibiting the same effort. Sceloporus jarrovi had the lowest reproductive effort, but showed an increasing effort with increasing age. These data suggest that the demographic environment may not be the primary selective pressure determining reproductive effort, and that reproductive effort may not be positively correlated with age in all species.