Predator-prey interactions are like an arms race, with both parties trying to one up each other to survive. Animals have developed many ingenious ways to escape predation, such as by startling, confusing, or actively repelling their predators.

Typically, when an animal notices its predator lurking around, it either pauses its routine to run away from the predator or tries a defensive tactic to ward it off. That is why scientists were puzzled to see what fruit flies (Drosophila melanogaster) do when predatory wasps are nearby: they increase their mating. This finding is detailed in a new paper published in Nature Communications. 

Since wasps specifically target fruit fly larvae, the accelerated mating made no sense to the researchers. They started by checking whether the increased mating was a result of changes in male or female flies or a combination of both. To resolve this, they paired off females and males exposed to wasps with both exposed and unexposed partners. It turned out that, wasp exposure was making only the female flies more interested in mating — males exposed to wasps weren’t observed to be more interested than unexposed males. Turning their focus solely on the females, researchers then used mutant fly strains with impaired hearing and vision to confirm that seeing the wasp was essential for heightened mating response. 

These initial observations led the researchers to question the nature of the response to wasps — was it immediate or lasting? They introduced a gap of two hours between wasp-exposure and mating, to test out the possible timespan of this response. They saw that the response was indeed temporary. Exposed flies mated as usual if enough time elapsed after being around the wasps.

Upon comparing gene expression profiles of wasp-exposed and non-exposed flies, researchers were able to identify ten genes that showed high expression levels only in wasp-exposed flies. Among them, the IBIN gene showed highest increase. When they gave flies a mutated copy of IBIN gene, those flies didn't show that accelerated mating behavior near wasps. 

The researchers propose that female flies probably prioritize successful mating over finding a suitable mate, because they anticipated the additional effort required for finding a safe egg-laying sites when surrounded by the wasps.