Influence of Water Potential on Growth and Survival of the Embryo, and Gas Conductance of the Egg, in a Terrestrial Breeding Frog, Pseudophryne bibroni

Abstract

The eggs of the Australian frog (Pseudophryne bibroni) are laid in wet conditions on land and subsequently experience a variety of hydrous conditions during incubation. In the laboratory, P. bibroni eggs were reared at water potentials ranging from 0 to -800 kPa. Within the embryonic tolerance range (approximately 0 to-200 kPa), the rate of embryonic growth (dry body mass/time) was greater in relatively wet conditions than in relatively dry conditions. The growth rate was approximately 65% greater at 0 kPa than at -100 and -200 kPa. This pattern has been shown previously for a number of reptiles but not amphibians. Development of P. bibroni through designated embryonic stages also proceeded faster in relatively wet conditions. The thickness and surface area of the egg capsule wall were substantially greater in relatively wet conditions than in relatively dry conditions. Because thickness and surface area have opposite effects on the oxygen conductance of the gelatinous egg capsule (GO₂), the effect of wat...