William H. N. Gutzke

Influence of the Hydric and Thermal Environments on Eggs and Hatchlings of Bull Snakes Pituophis melanoleucus

Eggs of bull snakes (Pituophis melanoleucus) were incubated at temperatures of 22.0, 27.0, and 32.0 C on substrates with water potentials of -150, -300, and -1,100 kPa using a 3 X 3 factorial design. The thermal and hydric environments affect fluxes in water between eggs and their surroundings during the course of incubation. Eggs incubated at low temperature (22.0 C) and on wet substrate (-150 kPa) gain the greatest amount of mass during incubation, while eggs incubated at high temperature (32.0 C) on dry substrate (-1100 kPa) lose the greatest amount of mass. The proportion of eggs that hatch is lower at the low temperature, while incubation at the high temperature results in a greater proportion of hatchlings with abnormalities. In general, eggs incubated at the intermediate temperature produce larger hatchlings than do eggs held at either low or high temperatures. While the hydric environment does not affect hatching success, eggs exposed to wet or moist hydric conditions give rise to larger hatchlings than do eggs exposed to dry conditions. Both temperature and water availability affect the composition of hatchlings.

Influence of Hydric Environment on Oxygen Consumption by Embryonic Turtles Chelydra serpentina and Trionyx spiniferus

Patterns of growth and metabolism by turtle embryos were examined in groups of eggs incubated on artificial substrates differing in water potential. Snapping turtle embryos in eggs incubated under wetter conditions attained larger size and consumed more oxygen than did embryos in eggs from drier conditions. Mass-specific oxygen consumption, however, was unaffected by hydric conditions of the incubation environment. No differences in growth patterns or oxygen consumption were observed in softshell turtle eggs in either treatment, although eggs on drier substrates lost significantly more mass than did eggs on wet substrates. The temporal pattern of oxygen consumption by turtle embryos resembles that of embryonic precocial birds, but total energetic costs of development in turtles are <50% of predicted costs for precocial birds of similar body mass.

Influence of Hydration of the Environment on Eggs and Embryos of the Terrestrial Turtle Terrapene ornata

Flexible-shelled eggs of the terrestrial turtle Terrapene ornata were incubated on wet (-150 kPa) and dry (-800 kPa) substrates at 29 C. Eggs on the wet medium absorbed water from the environment and increased in mass by 6% over the course of incubation, whereas eggs on the dry substrate lost water throughout development and weighed 17% less late in incubation than they did at oviposition. Availability of water to embryos had no apparent influence on hatching success, but embryos in the wet environment incubated longer, mobilized more of the nutrient reserve in their yolk, and grew larger before hatching than did those in the dry setting. Most of the ammonia released in catabolism of protein by embryonic Terrapene was detoxified by converting it to urea, which accumulated in eggs during incubation. In later stages of development urea attained concentrations inside eggs that may have been sufficient to inhibit metabolism of embryos, with the inhibition potentially being greater in dry settings than in wet environments. Differential inhibition of metabolism could have led to differences in rates of growth that contributed to the differences in size of turtles at hatching, The relatively large eggs of Terrapene ornata may represent the one adaptation of this species for development in terrestrial conditions, because large eggs of other turtles are more likely to hatch following incubation in a stressful hydric environment than are smaller eggs laid by conspecifics.

Skewed Sex Ratios for Adult and Hatchling Bullsnakes, Pituophis melanoleucus, in Nebraska

and may reflect a biased primary sex ratio in this population. Differences in the post-hibernation movements between sexes may have led to selection for the male bias noted. Females typically disperse less distance from hibernacula than do males and as such are more likely to compete for local resources with individuals more genetically similar to themselves than do males. Thus, clutches with sex ratios skewed in favor of males are expected to have less inter-sibling competition.