Sex ratio determination by queens and workers in the ant Pheidole desertorum

Because workers in colonies of eusocial Hymenoptera are more closely relate d to sisters than to brothers, theory predicts workers should bias investme nt in reproductive broods to favour reproductive females over males. Howeve r, conflict between queens and workers is predicted. Queens are equally rel ated to daughters and sons, and should act to prevent workers from biasing investment. Previous study of the ant Pheidole desertorum showed that worke rs are nearly three times more closely related to reproductive females than males; however, the investment sex ratio is very near equal, consistent wi th substantial queen control of workers. Near-equal investment is produced by an equal frequency of colonies whose reproductive broods consist of only females (female specialists) and colonies whose reproductive broods consis t of only males or whose sex ratios are extremely male biased (male special ists). Because natural selection should act on P. desertorum workers to bia s investment in favour of reproductive females, why do workers in male-spec ialist colonies rear only (or mostly) males? We tested the hypothesis that queens prevent workers from rearing reproductive females by experimentally providing workers with immature reproductive broods of both sexes. Workers reared available reproductive females, while failing to rear available male s. Worker preference for rearing reproductive females is consistent with qu eens preventing their occurrence in colonies of male specialists. These res ults provide evidence that queens and workers will act in opposition to det ermine the sex ratio, a fundamental prediction of queen-worker conflict the ory. (C) 2000 The Association for the Study of Animal Behaviour.