OXYGEN-TRANSPORT IN EGG MASSES OF THE AMPHIBIANS RANA-SYLVATICA AND AMBYSTOMA-MACULATUM - CONVECTION, DIFFUSION AND OXYGEN PRODUCTION BY ALGAE

Many amphibians lay their eggs in gelatinous masses up to 10-20 cm in diameter, posing problems for diffusive oxygen delivery. Oxygen may al so be provided by water convection between eggs or by oxygen productio n by endogenous algae. We studied egg masses of two local amphibians, Rana sylvatica and Ambystoma maculatum, to estimate the importance of each of these processes. We injected dye to check for water channels, measured oxygen partial pressures within egg masses to determine the i nfluence of external water convection and lighting, measured oxygen co nsumption and production in darkness and light and calculated expected gradients through egg masses with a cylindrical, homogeneous egg mass model. Rana sylvatica had relatively loose egg masses with water chan nels between the eggs; water convection was important for oxygen deliv ery. Ambystoma maculatum had firm egg masses with no spaces in the jel ly between eggs; thus, there was no opportunity for convective oxygen delivery. The egg masses were cohabited by Oophila ambystomatis, a gre en alga found specifically in association with amphibian egg masses. O xygen delivery in A. maculatum was by diffusion and by local productio n by the algal symbiont. Analysis of a cylindrical egg mass model and measurement of oxygen gradients through egg masses indicated that diff usion alone was not adequate to deliver sufficient O-2 to the innermos t embryos at late developmental stages. In the light, however, egg mas ses had a net oxygen production and became hyperoxic. Over the course of a day with a 14h:10h light:dark cycle, the innermost embryos were a lternately exposed to hyperoxia and near anoxia.