Skewed Sex Ratios in Snakes

Abstract

Fisher''s sex ratio theory predicts that parents should contribute the same effort to raise sons as daughters over the population as a whole. Sex ratios in the offspring of 3 live-bearing Australian snake species [Austrelaps superbus, Notechis scutatus, Pseudechis porphyriacus] were studied and published data on snake sex ratios at birth were reviewed. Most species produce young of each sex in equal numbers, but 1 elapid species, N. scutatus, produced a statistically significant excess of males (1.5:1). This imbalance is not consistent with Fisher''s theory. Two alternative models offer possible explanations, but the data are not sufficiently comprehensive to test either model.