THE EVOLUTION OF MATERNAL INVESTMENT IN LIZARDS - AN EXPERIMENTAL AND COMPARATIVE-ANALYSIS OF EGG SIZE AND ITS EFFECTS ON OFFSPRING PERFORMANCE

Used comparative and experimental analysis of egg size in a Sceloporus lizard to examine the presumed trade-offs among offspring number, offspring size, and performance traits related to offspring size that are likely to influence fitness. Mean clutch size among populations increased to the north (7 vs. 12 eggs/clutch, California vs. Washington), whereas egg size decreased (0.65 vs. 0.40 g). The elevational patterns in S California paralleled the latitudinal trends. Several offspring life-history traits that are correlated with egg size also varied geographically, eg incubation time, hatchling size, growth rate, and hatchling spring performance. Hatchling viability of experimentally reduced eggs was remarkably high (c70%), even when up to 50% of the yolk was removed. Northern eggs hatched sooner, in part because of their small size. Though growth rate is allometrically related to size within each population (smaller hatchlings grow faster on a mass-specific basis), population differences in growth rate are likely to reflect genetic differentiation in the underlying physiology of growth. The slower sprint speed of hatchlings from Washington compared to hatchlings from California is largely due to the fact that eggs are smaller in the former population. -from Author