Social structure and split sex ratios in the ant Pheidole pallidula

have investigated the social structure and reproductive allocation of the a nt Pheidole pallidula. Allozyme analyses indicate that (1) queens are singl y-mated, (2) both monogynous (single-queen) and polygynous (multiple-queen) colonies co-occur in the same population and (3) polygynous colonies may h ave anything from unrelated to full-sister queens. Sex ratios in this speci es were shown to be extremely split and we have tested the extent to which this colony-level sex ratio specialisation could be explained by (1) the re source level hypothesis (RLH) and (2) the relatedness asymmetry hypothesis (RAH). Our data show that the proportional investment in females was positi vely associated with total sexual productivity, which supports the RLH. In contrast to the expectation, relatedness among nestmate females was negativ ely correlated with relative investment in female reproductives. However, n o evidence was obtained for a concomitant decrease in relatedness asymmetry ; several trends in our data suggest that relatedness of females to male ne stmates decreases at least at the same rate as relatedness among female nes tmates, which implies that RA is either not correlated or positively correl ated with the degree of female bias in the sex ratio. The RA hypothesis can not therefore be refuted as an account of the split sex ratio in this speci es. Our study shows that the empirical testing of both the RLH and the RAH may become unexpectedly complex in social systems where both queen number a nd relatedness among queens vary, and that estimates of male-to-worker rela tedness are essential for testing the RAH in Such populations.