Maintaining a behaviour polymorphism by frequency-dependent selection on a single gene

In Drosophila, natural variation in the foraging (for) gene is behind a well known contrasting pair of behaviours in low nutrient conditions, the 'rover' and 'sitter' phenotypes. Despite decades of research, it has not been possible to account for the maintenance of allelic variation in for, and the maintenance of stable polymorphisms in general. New experiments reveal that competitive interaction between these coexisting variants could be the explanation. When one variant is common the other thrives, and vice versa, ensuring that 'sitter' larvae (inactive eaters that move infrequently and eat a lot) and 'rovers' (that move a lot and eat little) can coexist.