Maternal Manipulation of Offspring Phenotypes via Nest-Site Selection in an Oviparous Lizard

Mothers may be able to manipulate the phenotypes of their progeny not only via direct pathways (e.g., allocation of nutrients and energy), but also indirectly, by inducing particular developmental pathways through selection of nest sites and thus, incubation conditions. In the field, female skinks (Bassiana duperreyi) in montane southeastern Aus- tralia select nest sites with specific thermal characteristics-especially, a high mean tem- perature and a high diel range in temperature. Monitoring of 14 natural nests throughout most of the incubation period revealed considerable differences among nests in both means and variances of thermal regimes. Laboratory experiments on this species show that both the mean and the variance of incubation temperatures profoundly influence developmental rates (and hence, incubation periods) as well as the body shape, activity levels, thermo- regulatory behavior, and running speeds of the hatchlings. Hence, a female's selection of a particular nest site can substantially modify both the time of emergence of the hatchlings, and the morphology and behavior of her offspring. Even within a single nest, minor dif- ferences among eggs in their depth below the ground surface will directly affect thermal variance, and so may strongly influence rates of embryogenesis and the phenotype of the hatchling. The effects of thermal variance (independent of the mean) on embryonic de- velopment rates and hatchling phenotypes suggest that data from constant-temperature incubation in the laboratory should be interpreted with caution.