Influence of environmental oxygen on development and hatching of aquatic eggs of the Australian frog, Crinia georgiana

The effect of oxygen partial pressure (Po-2) on development and hatching wa s investigated in aquatic embryos of the myobatrachid frog, Crinia georgian a, in the field and in the laboratory. Eggs from 29 field nests experienced widely variable Po-2 but similar temperatures. Mean Po-2 in different nest s ranged between 2.9 and 19.3 kPa (grand mean 12.9 kPa), and mean temperatu re ranged between 11.9 degrees and 16.8 degreesC (grand mean 13.7 degreesC) . There was no detectable effect of Po-2 or temperature on development rate or hatching time in the field, except in one nest at 2.9 kPa where the emb ryos died, presumably in association with hypoxia. Laboratory eggs were inc ubated at 15 degreesC at a range of Po-2 between 2 and 25 kPa. Between 5 an d 25 kPa, there was almost no effect of Po-2 on development rate to stage 2 6, but the embryos hatched progressively earlier-at earlier stages and lowe r gut-free body mass-at lower Po-2. At 2 kPa, development was severely dela yed, growth of the embryo slowed, and morphological anomalies appeared. A h igh tolerance to low Po-2 may be an adaptation to embryonic development in the potentially hypoxic, aquatic environment.