Colony sex ratios, conflict between queens and workers, and apparent queencontrol in the ant Pheidole desertorum

Sex-ratio conflict between queens and workers was explored in a study of co lony sex ratios, relatedness, and population investment in the ant Pheidole desertorum. Colony reproductive broods consist of only females, only males , or have a sex ratio that is extremely male biased. Colonies producing fem ales (female specialists) and colonies producing males (male specialists) o ccur at near equal frequency in the population. Most colonies apparently sp ecialize in producing one reproductive sex throughout their life. Allozyme analyses show that relatedness does not differ within male-specialist and f emale-specialist colonies and they do not appear to differ in available res ources. In the population, workers are nearly three times more closely rela ted to females than males; however, the investment sex ratio is near equal( 1.01, female/male), which is consistent with queen control. Selection shoul d be strong on workers to increase investment in reproductive females, so w hy do workers in male-specialist colonies produce only (or nearly only) mal es? One hypothesis is that queens in male-specialist colonies prevent the o ccurrence of reproductive females, perhaps by producing worker-biased femal e eggs. An earlier simulation study of genetic evolution of sex ratios in s ocial Hymenoptera (Pamilo 1982b) predicts that such mechanisms can result i n the evolution of bimodal colony sex ratios and queen control. Results on P. desertorum are generally consistent with that study; however, informatio n is not currently available to test some of the model's predictions and as sumptions.