Fruit flies warn other species of wasp danger

Fruit flies can learn the dialects of other fly species after a period of living together, new research published in the journal PLOS Genetics reveals.

Like a mixed flock of songbirds sounding the alarm when there is a predatory hawk overhead, fruit flies of different species alert one another when there is a shared threat of parasitoid wasps.

The wasps prey on flies by using a needle-sharp ovipositor to insert their eggs into fly eggs, and the young wasps then feed on the developing flies. Previous studies on fruit flies (Drosophila melanogaster) have shown that when female flies are aware of parasitoid wasps, they respond by developing fewer eggs, thus risking less young to wasp attack.

The flies also communicate this information to other females using a series of wing movements. Having received the alarm, other flies develop fewer eggs, even if the wasp is unseen. This behaviour offers researchers an opportunity to study interspecies communication, using Drosophila as a model system.

The research team, led by Balint Z. Kacsoh of Geisel School of Medicine at Dartmouth, used wild strains of D. melanogaster for their study, as these were likely to retain a typical predator response. They housed the flies in small acrylic duplex compartments which allowed visual communication.   In the first series of experiments, a number of flies were stationed next to a compartment of wasps, (Leptopilina heterotoma) and then the wasps removed. The exposed flies were then known as teacher flies, who could communicate the threat to a new cohort of flies called naïve student flies. The physiological response (reduced egg development) was measured in the student flies.

The team repeated this procedure with closely related and distantly related fly species.  The findings reveal that the more closely related the species, the more readily they can communicate with one another.

But even distantly related fly species can learn to communicate with one another if they share the same living space for a period. In the study, flies of different species shared the same compartment for a week, and then the experiment was repeated.

“We find flies can communicate with one another about an anticipated danger, which is suggestive of a fly ‘language’,” says Kacsoh. “Living together enables the flies to learn new dialects composed of different visual and scent cues.”

Some species were capable of learning multiple dialects, revealing that the Drosophila have high neural plasticity or capacity for learning.  Already used for so many different fields of enquiry, this new research establishes the flies as a useful genetic model for studying the evolution of dialects.

Further genetic experiments by the team showed that learning another dialect requires a part of the brain called the mushroom body, which is the centre of learning and memory in flies.

“We plan to build upon our work by elucidating the neural circuitry that governs dialect learning,” adds Kacsoh.