The effect of incubation media on the water exchange of snapping turtle (Chelydra serpentina) eggs and hatchlings

Summary The effect of two different incubation media, sand and vermiculite, on the water exchange of eggs and the mass of hatchlings of snapping turtles (Chelydra serpentina) was assessed. The eggs were incubated fully buried in either sand or vermiculite at 30 °C and egg mass was measured periodically throughout incubation. The wet and dry masses of each hatchling and its residual yolk were measured at the end of incubation. The media had similar water potentials () but their thermal conductivities differed 2.8-fold. The eggs experienced a net water gain during incubation. The rates of water uptake between treatments were not statistically different throught the first 36 days of incubation but were statistically different thereafter, with eggs incubating in sand taking up water at about twice the rate of eggs incubating in vermiculite. Hatchling masses were similar to both media but hatchling water contents were significantly different. Hatchlings incubated in sand had lower water contents than hatchlings incubated in vermiculite even though the eggs in sand took up more water. Hatchling mass was correlated with egg water exchange for eggs incubated in vermiculite but not for eggs incubated in sand. The difference in egg water exchange in the two media appears to be attributable to differences in the thermal conductivity of the media. The presence of such a thermal effect supports the hypothesis that the eggs exchanged water with the media as water vapor. Egg water exchange was limited by the shell and shell membranes and not by the media. The shell and shell membranes appear to present an effective barrier to water uptake.Abbreviations M_H2O water flux (cm³·day^-1) - L_p hydraulic conductivity (cm·day^-1·kPa^-1) - A shell area (cm²) - A_p pore area (cm²) - l shell thickness (cm) - r pore radius (cm) - viscosity (kPa·day) - P_EH2O egg water potential (kPa) - P_AH2O medium water potential (kPa) - G_H2O water vapor conductance (cm³·day^-1·kPa^-1) - D_H2O diffusion coefficient (cm²·day^-1) - R gas constant (cm³·kPa·K^-1·cm^-3) - T temperature (K) - P_EH2O egg water vapor pressure (kPa) - P_AH2O medium water vapor pressure (kPa) - d egg diameter - K soil hydraulic conductivity (cm²·day^-1·kPa^-1) - DHM hatchling dry mass - WHM hatchiling wet mass - WU water uptake - IM initial egg mass