Sensitive Periods for the Influence of the Hydric Environment on Eggs and Hatchlings of Painted Turtles (Chrysemys picta)

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Abstract
Eggs of painted turtles (Chrysemys picta) were incubated in wet and dry environments. Half of the eggs in each treatment were transferred to the other treatment at the end of the first trimester, and a similar shift was performed at the end of the second trimester. Thus, eight experimental groups were recognized on the basis of hydric condition to which eggs were exposed in each trimester. The influence of the hydric environment on hatching success, on duration of incubation, and on size ofhatchlings is confined to the last two-thirds of incubation. The lack of effects associated with hydric conditions encountered by eggs during the first one-third of incubation can be explained by "compensatory water exchanges" that occur during the middle trimester. During the middle one-third of incubation, water uptake is greater and more rapid in a moist environment if an egg previously was in dry conditions than if an egg was in wet conditions. Likewise, water loss is more pronounced on a dry substrate during the middle trimester if an egg previously was in wet conditions than if an egg was in dry conditions. No compensatory water exchange occurs during the final trimester, but proximate hydric conditions during this period affect development. Because conditions in natural nests tend to fluctuate during the course of incubation, findings presented here tend to raise doubts regarding the significance of nest-searching behavior reported for females of many oviparous reptiles.