Science 322, 552 (2008)

Harvester ants develop into queens or sterile workers according to their genes as well as their environment, which had been thought to be the lone determinant of female caste.

Tanja Schwander, currently at Simon Fraser University in Burnaby, Canada, and Laurent Keller of the University of Lausanne in Switzerland noticed that some combinations of genes are more common in queen harvester ants (Pogonomyrmex rugosus) than in workers, and vice versa. So they crossed queens from six colonies with males of the same and different colonies to see what effect this might have.

The duo found that certain cross-colony pairings — and therefore particular gene combinations — reliably skewed the proportion of queens to female workers compared with the average.