As a reproductive strategy, sex has its pluses and minuses: it ensures genetic diversity but, unlike asexual reproduction, it means that parents pass on only 50% of their genes. Reporting in Science, Morgan Pearcy and colleagues show how the habits of one species of ant allow it to use a combination of both reproductive solutions to maximize advantage.

Ant colonies usually consist of large numbers of workers and a single queen, who is the only female to reproduce. In most ant species, haploid males are produced asexually, whereas sex is used to produce diploid females that develop into either workers or new queens. Pearcy and colleagues found an intriguing difference from this reproductive strategy in the ant species Cataglyphia cursor.

C. cursor is one of a small number of ant species in which unmated workers occasionally reproduce through a process known as automictic thelytokous parthenogenesis to produce females from an unfertilized egg. This involves meiosis, followed by fusion of two of the haploid products to produce diploid offspring. The authors studied the genetic make-up of 38 colonies of C. cursor, genotyping 4 highly polymorphic microsatellite markers in 532 workers. They found that a large majority of workers are produced by sexual reproduction, with only a small proportion being produced asexually. Unexpectedly, however, genotyping 56 new queens from different colonies showed that almost all were the result of automictic parthenogenesis by a queen — a different situation to most species, in which new queens are produced sexually.

The production of new queens in this way leads to a high degree of relatedness between queens and a high level of homozygosity that might be expected to reduce queen survival. However, unlike other species, where new queens set up new colonies on their own, in C. cursor they mate before they leave their colony and take adult workers with them. So, the authors suggest that optimum fitness among queens is less crucial than in other species. This allows genetic diversity to be maintained in the colony through sex, while the queen maximizes the propagation of her own genes through the asexual production of her successors.

This study illustrates the diversity of reproductive strategies among social insects — a feature that can provide important insights into the relative merits of sexual and asexual reproduction.