Do Changing Moisture Levels during Incubation Influence Phenotypic Traits of Hatchling Snakes (Tropidonophis mairii, Colubridae)?

Abstract

Phenotypic traits (e.g., size, strength, speed) of hatchlings in many reptile species are influenced by hydric conditions in the nest. Previous experiments have focused on comparisons between eggs maintained under constant (but different) conditions, but eggs in natural nests frequently experience strong temporal shifts in soil water content during incubation. Keelback snakes (Tropidonophis mairii) in the Australian wet-dry tropics nest over most of the year, so early nests experience decreasing water availability during development, late nests experience increases, and others (midyear) remain stable in this respect. We mimicked these three conditions and incubated 54 eggs (nine from each of six clutches) in a split-clutch design to maintain the same average water content but with differing trajectories through incubation. The experimental treatments significantly affected the total amount of water taken up by the eggs (and thus final egg mass), but incubation periods were unaffected. Hatchling size but not strength showed minor but statistically significant effects of incubation regimes. The ability of keelback eggs to take up excess water whenever it becomes available (either early or late in development) and to retain it even when conditions change buffers embryogenesis effectively (but not completely) against fluctuations in soil water conditions.