Incubation conditions as potential factors limiting the northern distribution of snapping turtles, Chelydra serpentina

We incubated snapping turtle eggs at extreme levels of temperature and moisture to test the hypothesis that incubation conditions limit the species' range by affecting hatching success and posthatching survival and growth. We also tested for local adaptations to cold incubation conditions by comparing the responses of embryos and hatchlings from a population near the northern limit of the species' range with those from a population farther south. Eggs of 20 clutches from two Ontario populations were incubated at 21.1 or 25.3 °C at one of three substrate moisture levels (−150, −300, −800 kPa), and hatchling survival and growth were monitored in the laboratory for 23 months. Hatching success, hatchling survival, and posthatching growth were lowest among turtles from eggs incubated at 21.1 °C. They were also uncoordinated and had poor control of their buoyancy. Hatching success was reduced in the drier substrates, but posthatching survival and growth were not affected by substrate moisture. Embryo and hatchling survival were lower in turtles from the southern population (which may be related to contaminants in the eggs) but hatchlings from that population grew the fastest. Hatching success at 21.1 °C or in the driest substrate did not differ between the two populations, but embryos from the northern population did show a greater increase in mortality at 21.1 °C relative to 25.3 °C than embryos from the more southerly population. The effects of lower incubation temperatures may be the most important factor limiting the northern distribution of this species, because lower temperatures during incubation and a shorter growing season probably reduce both the quantity and quality of hatchling turtles produced at northern sites.