Together with researchers from, among others, the University of Gothenburg, Axel Wiberg, developmental biologist at Stockholm University, has studied the mating game of dance flies. When they are about to mate, the females swarm in large groups and the males approach from below the swarm and scope out their potential partners. To increase their chances of spreading their genes, the males target females that appear to have many eggs.
One can usually see this by the fact that they have a large abdomen. In this case, the females also have larger legs with more hair to appear large and powerful, says Axel Wiberg, one of the researchers behind the study.
Protein supplement as a gift
Before mating, the males also bring a gift, often a dead insect, which they present to the females. The females rarely hunt themselves, but they need protein to produce eggs. This is where the trickery begins – by faking that they have eggs, they can deceive the males into providing them with food even though they don't have any.
The females have tricks to appear as if they have many eggs. They swallow air that fills their abdomens, and to appear powerful when swarming, they have developed hair on their legs and their wings can be larger and darker, says Axel Wiberg.
Appearance is important
That animals imitate, behave, and have special appearances to attract the opposite sex is nothing new, it's common, not least among birds, where it's often the males that are decorated. But now, the researchers have seen that within the species where the females have developed the hairiest legs, the males have the most enlarged eye facets. The facets are the small individual eyes that insects see with.
We believe there is a connection and that they have evolved in tandem, says Axel Wiberg.
The researchers think that this sexual game can lead to the evolution of the species, but whether the males with better vision can actually see through the bluffers, the researchers don't know yet.
