Evolution. Sex...only if really necessary in a feminine monarchy.

C RE D IT :M A RC O U LI A N A T he honey bee society was famously described as “The Feminine Monarchy” by the cleric Charles Butler in 1634. Honey bees and their relatives—including all hymenopteran societies—qualify for this label because their colonies are headed by one or a small number of fertile queens. These queens produce a large number of sterile or nearly sterile daughter workers and, later, with their assistance, produce a smaller number of fertile sons and daughter queens (1). The complex and diverse life cycles and social organization of the feminine monarchies are matched by their equally complex and diverse strategies for sexual and asexual reproduction (2). On page 1780 of this issue, Pearcy et al. (3) uncover a new dimension in the complexity of hymenopteran reproduction. In the Hymenoptera, males are typically haploid and females are diploid (see the figure). It has been shown that sex is determined by a highly variable sex determination locus such that homozygosity (a very rare possibility, given the low probability of a female mating with a male having the same allele as herself) or hemizygosity (expected in all haploid individuals) results in male development, whereas heterozygosity results in female development (4). In social Hymenoptera, virgin queens make nuptial flights during which they acquire sperm from one or more males and store and nurture the sperm in their spermatheca—a tiny gland that opens into the oviduct. Queens have perfect control over the sex of their offspring. To produce daughters, a queen lets sperm flow from the spermatheca into her oviduct and then lays fertilized diploid eggs. Whether the diploid eggs develop into sterile workers or fertile queens depends on the nutritional environment of the young larvae. To produce sons, however, a queen prevents the flow of sperm into the oviduct and lays unfertilized haploid eggs. Such parthenogenetic development of males—known as arrhenotoky—is a universal and well-known feature of the Hymenoptera. Less widely known (and apparently rather infrequent) is another form of E V O L U T I O N