TEMPERATURE, TIME, AND REPTILE EGG WATER EXCHANGE

ABSTRACT

The effect of incubation temperature (T, °C) on the developmental rate (R_d, days⁻¹) and water exchange of reptile eggs is examined. The relationship between R_d and T can be described using the Arrhenius equation. The free energy (E) of this relationship is around 50 kJ·mol⁻¹, equivalent to a Q₁₀ of 2, for all the species examined. The data indicate that the R_d's of reptile eggs are sensitive to changes in T to about the same extent. However, there may be biologically important variation in sensitivity to T. The thermal tolerance range (TTR) of reptile eggs, on the other hand, varies substantially but appears to be around 10°C or less. Egg water exchange on a rate basis ([Mdot]_H2O, mg·day⁻¹) is influenced by T and increases by a factor of around 1.9 for every 10°C increase in T. The change in [Mdot]_H2O with T is offset by the increase in R_d which decreases the incubation period (I, days) so that total egg water exchange (M_H2O, g) is not influenced by T for eggs whose R_d's have Q₁₀'s around 1.9. Eggs whose R_d's diverge from 1.9 should demonstrate a progressive effect of T on M_H2O. The [Mdot]_H2O and M_H2O of eggs is influenced by the thermal conductivity of the medium in which the eggs incubate. This occurs because the vapor pressure of the egg during incubation will change relative to the vapor pressure of the medium due to the influence of medium thermal conductivity on metabolic self-heating by the egg.