Laboratory and field experiments identify sources of variation in phenotypes and survival of hatchling lizards

To understand the process of natural selection, relationships between phenotype and fitness and sources of phenotypic variation must be known. We examined the importance of incubation moisture conditions, maternal yolk investment, and clutch (genotype) to phenotypic variation in hatchlings of the lizard Sceloporus undulatus. Eggs were distributed among two moisture treatments and a third treatment in which yolk was removed. After hatching, mass, snout–vent length, tail length, body shape, thermal preference, running speed, desiccation rate, and growth rate were measured for each hatchling in the laboratory. Hatchlings were then released at a field site in order to monitor growth and survival under natural conditions. Hatchlings from the dry and yolk-removed treatments were significantly smaller than those from the wet treatment. However, neither performance nor survival were affected by moisture or yolk removal. All phenotypes were affected by clutch. Clutches that produced relatively large hatchlings had higher survival than clutches that produced relatively small hatchlings. Furthermore, clutches that produced relatively slow growing individuals and fast runners had higher survival rates than clutches that produced relatively rapid growing individuals and slow runners. Our results emphasize the overriding importance of clutch (genotype) to variation in phenotypes and survival in hatchling S. undulatus.