Hatching Success of Turtle Eggs Exposed to Dry Incubation Environment

We tested the hypothesis that large eggs of a terrestrial turtle when exposed to stressful hydric environments are more likely to hatch than are small eggs of an aquatic turtle. Eggs of terrestrial Terrapene carolina were compared to eggs of two aquatic species; Trachemys scripta, whose eggs are similar in size to those of T carolina, and Chrysemys picta, with smaller eggs than either of the other two species. Eggs of all three species were incubated on wet and dry substrates with nominal substrate water potentials of -150 kPa and -1500 kPa, respectively. Overall, eggs of all three species on wetter substrate gained mass during incu- bation, whereas eggs on the drier substrate either gained less mass (T carolina) or lost mass (T scripta and C. picta) during incubation. Eggs of T carolina on the dry substrate gained more mass during incubation than did eggs of either of the aquatic species on wet substrate. The ability of eggs of T. carolina to maintain a positive water balance on a substrate with water potential less than -300 kPa is unique among turtles that lay flexible-shelled eggs. All three species are consistent in that hatchlings from wetter substrate tended to incubate longer, to be heavier, and to have longer carapaces than those from drier substrate. The pattern of survivorship on the dry substrate did not support the hypothesis that larger eggs are more likely to survive to hatch than are smaller eggs when exposed to a stressful environment because survivorship was equivalent between larger eggs of T. carolina and smaller eggs of C. picta. In contrast, survivorship of T scripta eggs was reduced compared to the other two species despite the relatively large egg size of T scripta.