Family break-ups lead to domestic violence in fruit fly relationships

Male fruit flies with strong family ties are less likely to become abusive during mating than others, according to new research.

Drosophila melanogaster (fruit flies) courtship is known to be a violent affair. Males compete aggressively for a female’s attention, attacking each other with their front legs - often harming the object of their affection in the cross fire. 

Recent studies have suggested that when two males are related, this fighting tends to be less intense and therefore less harmful for the females involved. However, it has found that family bonds are not the only factor that affects the ferocity of fly courtship: the rivals have to like each other too.

This study tested the role of relatedness and familiarity in the fly mating process by placing trios of virgin male flies with individual virgin females and allowing them to feed and mate freely. The team then compared the behaviour and lifespans of the flies in each group by testing brothers that grew up together, brothers that had been separated at birth, unrelated males that grew up together, and unrelated males that never knew each other.

“Theory suggests that if males are related, then they should be nicer to each other and harm females less as a result, but this is not strictly true,” said Sally Le Page, a D.Phil student in the Zoology Department and lead author of the study. 

“What we found were that females are harmed least by males that are both related and familiar, i.e. brothers that grew up together.”

These findings show that familiarity is as important as relatedness in fly courtship, and that brothers that had grown up together were significantly nicer to the female during courtship than the brothers that had grown up apart.

The findings have the potential to shed light on the role that familial bonds have on species’ social relationships - including humans who show the effects of inclusive fitness and developing certain social behaviours. 

However, Le Page stresses: “We are not saying that, based on these findings, as a woman you should sleep with the housemate brother of your previous partner – that is a bit of a stretch. There are species caveats that do not cross over. However, it is testing the same framework that can apply to everything.”

With further research there is scope to use the study’s lessons around the factors that make females produce more or less offspring, in the field of conversation and wider pest controller.

To read the full paper: