Patterns of variation in female-biased colony sex ratios in a social spider

Colonies of a social spider Achaearanea wau (Theridiidae) from Papua, New Guinea have adult and juvenile sex ratios that are biased towards females, and this probably represents a primary bias at the egg stage. Adult sex ratios are less female-biased than are juvenile sex ratios, and both vary significantly among colonies. Adult sex ratios covary with colony size: small colonies have a larger proportion of males than large ones. The pattern of variation in adult sex ratio may be due to greater mortality of females than of males during maturation. Juvenile sex ratios do not covary with colony size, nor do they differ among populations. Colony size, however, does have a significant effect on survival and dispersal in colonies. I conclude, therefore, that a conditional sex ratio strategy, in which the primary sex ratio of the colony is adjusted to changing demographic patterns, does not occur in A. wau. I suggest that environmental heterogeneity acting on individual reproductive output may be responsible for the observed variation among colonies in juvenile sex ratios.