Compensation for inundation‐induced embryonic diapause in a freshwater turtle: achieving predictability in the face of environmental stochasticity

Abstract

Summary We investigated the influence of duration of inundation‐induced diapause, incubation temperature and clutch of origin on incubation duration and survivorship of eggs of the Snake‐Necked Turtle, Chelodina rugosa, from the wet–dry tropics of northern Australia. Eggs of C. rugosa survive at least 25 weeks’ inundation, almost 6 months, with a clear optimal inundation duration of 6 weeks. Eggs not held under water suffered the same mortality as eggs inundated for 25 weeks. Underwater nesting is not a facultative capacity but, rather, inundation is essential for optimal survivorship of embryos. Inundation duration had a profound effect on incubation period, reducing it by up to 9 weeks over what would be expected for a given temperature. Eggs inundated for up to 7 weeks complete incubation faster than had they been laid at the same time in dry ground. There was remarkable variability in incubation period remaining after correcting for the effect of incubation temperature, inundation duration and clutch. We interpret these traits as adaptations that match the timing and duration of the period available for nesting to the timing and duration of the period available for successful hatching, emergence from the nest and hatchling survival. Our interpretation is placed in the context of considerable environmental stochasticity in the factors driving these variables.