Intermittent hypoxia in eggs of Ambystoma maculatum:: Embryonic development and egg capsule conductance

The spotted salamander Ambystoma maculatum breeds in shallow freshwater pools and imbeds its eggs within a common outer jelly matrix that can limit oxygen availability. The eggs are impregnated with the unicellular alga Oophilia amblystomatis, which produces oxygen during the day but consumes oxygen at night. This daily cycle of algal oxygen production drives a diurnal fluctuation of oxygen partial pressure (P-O2) within the eggs, the magnitude of which depends on the distance of an egg from the exterior of the jelly matrix and on the ambient P-O2 of the pond. We subjected A. maculatum eggs to fluctuating oxygen levels with a variable minimum P-O2 and an invariable maximum, to simulate natural conditions, and measured differences in developmental rate, day and stage at hatching, and egg capsule conductance (G(O2)). Lower minimum P-O2 slowed development and resulted in delayed, yet developmentally premature hatching. G(O2) increased in all treatments throughout development, but P-O2 had no detectable effect on the increase. Intermittent hypoxia caused comparable but less pronounced developmental delays than chronic hypoxia and failed to elicit the measurable change in G(O2) seen in ambystomatid salamander eggs exposed to chronic hypoxia.