More than a century ago, early geneticists showed that the inheritance of a single mutation by fruit flies can change the insect’s body color and simultaneously disrupt its mating behavior.

The studies, performed in the laboratory of Thomas Hunt Morgan, were the first to demonstrate that some behaviors have a genetic basis. The fruit fly experiments also provided an early example of pleiotropy, a phenomenon in which a single gene has the ability to influence multiple traits.

In the decades that followed, scientists have been unable to satisfactorily explain how a single genetic mutation was able to change a male fruit fly’s body color from brown to yellow and at the same time affect mating behavior. Some researchers suggested the mutation caused brain changes that interfered with mating.

But in a study published Oct. 15 in the journal eLife, University of Michigan biologists show that the solution to the yellow fly mystery is not in the insect’s tiny brain. Instead, it has to do with changes in the morphology of specialized leg structures called sex combs.

The researchers used a series of genetic screens and high-speed video recordings of mating to demonstrate that male yellow flies lacking pigments in sex combs were unable to grasp females for mounting and copulation following courtship. The findings explain why yellow flies mate poorly and also reveal why fruit flies possess sex combs, which are modified bristles on the front legs with previously unknown function.

In addition, the study’s results could eventually have applications in the pest-control industry and in public health, according to study first author Jonathan Massey, who did the work as part of his doctoral dissertation in the U-M Department of Ecology and Evolutionary Biology. His adviser was EEB’s Patricia Wittkopp, who is a senior author on the eLife paper.

“We aimed to solve the yellow fly mystery because the answer would help better explain how genes controlling animal morphology could also influence animal behavior,” said Massey, who is now a postdoctoral research fellow at Harvard Medical School and Boston Children’s Hospital.

“If, for example, pest managers have a clearer understanding of how individual mutations cause critical disruptions in mating success, they could develop targeted strategies to block reproduction in species that transmit disease or destroy crops.”

Read full Michigan News press release

Read the eLife paper: The yellow gene influences Drosophila male mating success through sex comb melanization