Food odour gates courtship in Drosophila erecta flies

Researchers studying the fruit fly Drosophila erecta report in Nature that mating in this species is strictly contingent on the ecological and social environment created when flies aggregate densely on a food patch doi.org. Food volatiles directly raise male sexual arousal, so males sample and pursue potential mates, which produces dynamic interactions across the group doi.org. In the experiments, males were placed alone or with other flies, in air with apple cider vinegar odour (imitating fermenting fruit) or without odour.

Food odour as a sensory gate

Without the odour, D. erecta males stayed motionless and showed no interest in other flies. With vinegar odour they courted intensely any nearby fly, male or female, until they found a partner. Nine of ten matings took place in the zone where the vinegar had been sprayed.

In D. melanogaster, food odour can promote arousal doi.org, but it is dispensable for vigorous courtship doi.org. In the experiments, these flies mated both with and without vinegar odour and spread evenly over the available space. Comparative circuit analyses show that species-specific thresholds for sexual arousal reflect variation in how olfactory input modulates conserved nodes controlling courtship drive doi.org. As a result, food volatiles act as a strict sensory gate only in D. erecta doi.org.

Visual feedback in the group

The motion of neighbouring flies transforms each male's visual field, which further amplifies his arousal and creates a multisensory feedback loop that promotes courtship across individuals doi.org. According to the report, the visual neurons of D. erecta became active only in the presence of food odour, and males were drawn towards the more crowded zone. In groups, males courted more vigorously than when only a female was present.

Vanessa Ruta, head of the laboratory, said that this feedback gives rise to collective behaviour of the kind seen in fish schools, bird flocks and locust swarms, and that olfactory information acts as a rigid filter changing the weight of visual cues. The authors conclude that environmental cues not directly tied to sexual signalling can reorganize the social landscape so that mating occurs where reproductive opportunities are abundant doi.org. D. erecta feeds on the fruit of Pandanus candelabrum from Senegal and Cameroon, which is available for only two to four months a year.

Food odour gates courtship in the fruit fly Drosophila erecta, and group motion amplifies male arousal

Food odour as a sensory gate

Visual feedback in the group

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