Embryonic Respiration and Oxygen Distribution in Foamy and Nonfoamy Egg Masses of the FrogLimnodynastes tasmaniensis

We measured embryonic oxygen consumption (V̇o2) and profiles of O2 partial pressure (Po2) in the egg masses of Limnodynastes tasmaniensis from two populations that produce either floating foam nests or submerged nonfoamy nests. The nests remained aerobic but became hypoxic during development in well-aerated water. As V̇o2 increased, anoxia in the central eggs was generally avoided by changes in nest structure. In the field, foamy nests floated at the surface in betteroxygenated water while nonfoamy nests were also supported by aquatic vegetation near the surface. Some embryos became anoxic and died when the egg masses were artificially placed on the bottom. Numerical models of O2, diffusion through egg masses confirmed the absence of convection in L. tasmaniensis nests but indicated that convection may be required in larger aquatic egg masses of other species. The models also demonstrated local depression of Po2 around individual eggs in the clutch and indicated that all O2 entering the perivitelline space is used by the embryo and none is released to eggs deeper in the mass.