Sexual differences as adaptation to the different gender roles in the frog Xenopus laevis Daudin.

1. Various physiological parameters were determined in fed, adult, male and female Xenopus laevis acclimated to 20 degrees C and with a light: dark cycle of 12:12. The results were compared for sex differences. 2. There were significant differences in food intake, oxygen consumption, and motor activity with lower values for each parameter in males than in females (Table 1). 3. Further significant differences were found in the plasma concentrations of calcium, total lipids, and aldosterone (Table 3), in the somatic indices of fat body and gonads, in the glycogen and protein content of the liver (Table 4), and in the activities of glucose-6-phosphate dehydrogenase, fructose-1,6-diphosphatase, and phosphoenolpyruvate carboxykinase in the liver (Table 5). 4. It is assumed that the observed differences are essentially a result of differences in body growth and gametogenesis between the sexes. The lack of capacity of males to store glycogen and lipids in the male gonads is a further explanation for the differences.