Extreme reproductive specialization within ant colonies: some queens produce males whereas others produce workers

A key feature differentiating animal societies is the partitioning of reproduction among breeders. We studied how reproduction is partitioned among nestmate queens of the ant Formica exsecta in laboratory colonies. In polygynous (multiple-queen) colonies, queens can increase their reproductive success by laying more eggs or by increasing the proportion of eggs that develop into reproductive individuals instead of workers. We found that reproductive skew among queens for egg production was low, but that 84% of all queens contributed exclusively to one type of brood, either males or workers (no new queens are produced in the laboratory). Furthermore, our data revealed that the degree of reproductive specialization among queens significantly increased during brood development. Contrary to predictions of most reproductive skew models, the extent of reproductive skew was not associated with relatedness among co-breeding queens. We also found no association between the pattern of queen specialization and relatedness between queens and their mates. Such an association would occur if queens mated to related males specialize in male production to avoid the cost of inbreeding. Altogether, our findings show a yet undescribed pattern of reproductive specialization among nestmate queens in ants and emphasizes the need to investigate reproductive contributions of queens for each type of offspring separately.