Influence of Environmental Po2 on Embryonic Oxygen Consumption, Rate of Development, and Hatching in the Frog Pseudophryne bibroni

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Abstract
Embryos of the frog Pseudophryne bibroni develop on land in depressions underneath objects or vegetation. They hatch only after they have reached Gosner stage 26-27 and are flooded with water. Flooding of the nest reduces outside the eggs owing to O₂ consumption by the embryos. Low limits the rate of O₂ consumption ( ), retards embryonic development, and triggers hatching. In terrestrial embryos at the hatching stage at 12 C, becomes severely limited at below 14.7 kPa (111 mmHg). In embryos raised in water, rate of development decreases with decreasing below 38.0 kPa (285 mmHg). In embryos raised on land and then flooded, hatching occurs in less than 12 h when of the gas above the water is less than 29.9 kPa (224 mmHg). In contrast, hatching of nonflooded embryos on either wet or dry substrate occurs within this time interval only when is below 5.2 kPa (39 mmHg). This difference in hatching response is apparently due to O₂ depletion in the water surrounding the aquatic eggs rather than to differences in water potential of the environment. Thus, hatching is not immediately stimulated within a range of that limits (5.2-14.7 kPa). Hatching occurs only after protracted flooding, which may help ensure that the hatchling emerges into enough standing water to complete metamorphosis.