FINKLER, M.S.; Indiana University Kokomo: Variation in soil water content influences the size of laboratory-reared Chelydra serpentina hatchlings from eggs incubated in natural nest soil.

Most studies that have investigated the influence of hydric conditions during incubation on reptile hatchling phenotype have employed either vermiculite or sand as incubation media, and the applicability of data derived from eggs using one media type or the other to natural population has had considerable debate. However, few studies have employed soil from actual nesting areas as the incubation media. In this study, we tested the influence of variation in substrate water content on the size of hatchling snapping turtles from Southeast Michigan using soil collected from naturally-formed snapping turtle nests form the same location. Eggs from five clutches were fully buried in sterilized soil that had been dried then reconstituted to six different levels of hydration (3, 5, 7, 9, 11, and 13% gravimetric water content). Changes in egg mass over the course of incubation correlated linearly with the relative water content of the soil. Moreover, mass at hatching correlated linearly with the relative water content of the soil. These findings support the hypothesis that variation in soil hydration can influence the size of hatchlings emerging from natural nests. Moreover, these findings suggest that models describing the effects of hydric conditions on embryonic development in the eggs need to consider the impact that heterogenous particulate size and organic content may have on the matric water potential and thermal conductivity of soils in natural nests.