Effects of hypoxia on embryonic development in two Ambystoma and two Rana species

Oxygen available to amphibian embryos fluctuates widely and is often very l ow. We investigated the effects of oxygen partial pressure (1.3-16.9 kPa) o n embryonic development and hatching of two Salamander (Ambystoma) and two frog (Rana) species. In Ambystoma, chronic hypoxia resulted in slowed devel opment, delayed hatching, and embryos that were less developed at the time of hatching. Although hypoxia was not lethal to embryos, temporary developm ental abnormalities were observed in Ambystoma at oxygen partial pressures of 3.8 kPa and below Posthatching survival decreased below 3.3 kPa. In Rana , hypoxia did not affect developmental rate, presumably because hatching oc curs at a very early stage of development relative to Ambystoma. However, R dna embryos hatched sooner in hypoxia than in normoxia, resulting in less d eveloped embryos at the time of hatching. The results suggest that embryoni c hypoxia may negatively affect survival and fitness in these species.