Researchers have found that for dancer flies, it is crucial that the male offers a gift to the female before mating takes place. — AFP
In the animal kingdom, seduction is often the business of males, who display various attributes to attract females. However, in dancer flies, the opposite is true.
Females inflate their abdomens with air and flaunt their hairy legs to appear bigger in the eyes of the males they covet. But the latter, far from being fooled, have honed their vision over the course of evolution, and are no longer fooled.
A study published in the journal Evolution sheds light on a fascinating evolutionary duel in the world of flies. For the first time, researchers at the University of Gothenburg, and University of Stockholm in Sweden have demonstrated that males too can develop traits that enable them to outwit the manipulative strategies of females during courtship.
By observing several species of dancer flies, they discovered an intriguing correlation between how richly decorated the female flies are and how large the eye facets are on males. This adaptation enables them to better identify truly fertile females and avoid those who try to trick them.
In these flies, courtship is based on an exchange of food. Before mating, the male offers a gift to the female, usually a dead insect. This offering is crucial for reproduction, as females, who are reluctant to hunt, depend on this protein supply to produce their eggs. Without this “nuptial gift”, no mating takes place.
Some females, still devoid of eggs, use subterfuge to simulate advanced fertility and obtain an extra ration of food. They artificially inflate their abdomens, darken their wings and develop hair-covered legs to seduce the most generous males.
Researchers have found that for dancer flies, it is crucial that the male offers a gift to the female before mating takes place. — AFP
This rivalry between the sexes gradually influenced the visual perception of males. By studying the eye facets of several specimens, the researchers made a surprising discovery. In some species, the facets on the top of the eyes are larger than those at the bottom, a detail that plays a key role.
During mating, the male approaches the female from below, and this improved visual acuity helps a male to distinguish a truly fertile partner from an intriguing trickster.
Luc Bussière, evolutionary biologist at the University of Gothenburg and co-author of the study, believes that this mechanism illustrates an ongoing evolutionary process.
“This sexual play may force an evolution of the species. For generations, male flies with the largest facets have been favoured in mating and their genes are passed on. We see this as an evolutionary system where the development of different traits in male and female flies has been alternating,” the researcher explains in a news release.
But if the males’ vision improves, how will the females react? According to Axel Wiberg, one of the study’s authors, they are likely to develop new strategies to maintain their deceptive advantage.
One detail is already intriguing the researchers. In species where males have the largest eye facets, females also appear to have slightly enlarged facets, but only on the lower part of their eyes.
This physical feature is still unexplained, but it could represent a new tactic in the evolutionary struggle between the sexes. It may, for example, enable females to identify the most successful males more quickly, or to find their way around swarms during mating dances.
While the mystery remains to be unravelled, this study sheds light on some astonishing seduction behaviours in dancer flies. And it seems that, in this evolutionary duel, seduction is a never-ending battle. – AFP Relaxnews
