OUFIERO, C.E.*; ANGILLETTA, M.J.; Indiana State Univ., Terre Haute: It�s not just the size; it�s what�s inside that counts: Female size, egg size, and egg composition in the lizard Sceloporus undulatus.

Morphological constraints are thought to produce non-adaptive variation in egg size. For example, the size of a female�s pelvis may force her to produce eggs that are smaller than optimal size. In the eastern fence lizard (Sceloporus undulatus), smaller females produce smaller eggs, consistent with the hypothesis of pelvic constraints. However, females may alter the composition of their eggs to compensate for limits on egg size. To evaluate this hypothesis, we examined the size and composition of eggs of females from 6 populations of S. undulatus, which span the range of body sizes observed in this species. Eggs produced by smaller females had a higher energy density, which partially compensates for the reduction in egg size. This trend was observed within and among the six populations of S. undulatus. Our result suggests adaptive allocation of resources by females, but raises an intriguing question: Why don�t larger females produce smaller, more energetically dense eggs? Producing a smaller egg of equal energy content may have implications for water uptake, gas exchange, and other processes.