Effects of Thermal and Hydric Environments on Incubating Eggs and Hatchling Traits in the Cobra, Naja naja atra

We examined in the laboratory the effects of thermal and hydric environments on incubating eggs and hatchling traits of Naja naja atra collected from a population near the northern distributional limit of the species in Zhejiang, eastern China. Eggs were incubated at temperatures of 24, 26, 30, and 32 ?C on substrates with water potentials of 0 and -220 kPa using a 4 x 2 factorial design. Temperature strongly affected hatching success, incubation length, water uptake by eggs during the course of incubation, and most morphological hatchling traits examined; it even affected embryonic mobilization of inorganic material from the shell. Hatching success was higher at 26 and 30?C but lower at 24 and 32?C. Eggs incubated at 26 and 30?C produced larger and heavier hatchlings that also contained more inorganic material and energy than did eggs incubated at lower and higher temperatures. Hatchlings from eggs incubated at 24 and 32?C were similar in size and mass, but hatchlings from eggs incubated at 32?C had larger residual yolks. De- formed hatchlings were found at 24, 30, and 32?C, the frequency being independent of incubation temper- ature. At the time of hatching, shells from eggs incubated at 24?C had greater dry mass and contained more ash, suggesting that less inorganic material was withdrawn from the shell by embryos developing at 24?C. Compared with temperature, water potential was not an important source of variation for the hatchling traits we examined, although it did influence water uptake by eggs during incubation and hatching success at 24?C. The effects of temperature were independent of the effects of water potential. Variation in size and mass induced by incubation temperature may be important to posthatching survival and fitness of hatch- lings.