Drosophila erecta: food odour and group motion drive courtship

Researchers report in Nature that mating in the fly Drosophila erecta is strictly contingent on the ecological and social environment created when flies aggregate densely on a food patch doi.org. In the experiments, groups of five males and five females were placed in a 190 mm arena with a central 21.5 mm agar patch, either plain or scented with apple cider vinegar (ACV) as a generic host odour doi.org. The same design was used for the close relative Drosophila melanogaster, so that the two species could be compared doi.org.

Flies were fed and kept as virgins, which minimised their motivation to approach the odour for metabolic needs or in search of an egg-laying site doi.org. Both species feed on yeast that metabolise decaying fruit and are attracted to fermentation volatiles, which is why ACV was chosen doi.org.

Food odour and a visual feedback loop

The authors found that food volatiles directly promote male sexual arousal in D. erecta. They trigger males to sample and pursue potential mates, which produces dynamic interactions across the group doi.org. The resulting visual motion transforms each male's visual field and further amplifies his arousal. The authors describe this as a multisensory feedback loop that promotes courtship across individuals doi.org. D. erecta males are highly sensitive to the increase in visual motion, in contrast to D. melanogaster, they report doi.org.

The authors link this dependence to the species' ecology. Reproduction and population density in D. erecta are tightly tied to the seasonal availability of its host fruit, the screwpine Pandanus, which leaves a narrow window for individuals to meet and mate doi.org.

Species-specific thresholds in the circuit

In D. melanogaster, food odour can promote arousal but is dispensable for vigorous courtship doi.org. Comparative circuit analyses show that species-specific arousal thresholds reflect variation in how olfactory input modulates conserved nodes controlling courtship drive. As a result, food volatiles act as a strict sensory gate only in D. erecta doi.org.

The authors conclude that environmental cues not directly tied to sexual signalling can strongly influence reproductive behaviour. According to them, such cues also reorganise the social landscape, so that mating occurs where reproductive opportunities are abundant doi.org.

Drosophila erecta males court only amid food odour and group motion, experiments show

Food odour and a visual feedback loop

Species-specific thresholds in the circuit

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