Food perception alone stimulates oviposition through serotonin signaling in Drosophila

Reproductive output in fruit flies can be rapidly stimulated through sensory perception of dietary yeast, even before the flies consume the nutrient, according to a study using Drosophila melanogaster. The researchers found that mere exposure to the odor of yeast, a protein-rich food source often used to stimulate fecundity in the fruit fly, increased the rate of oviposition and the number of eggs laid within hours. Importantly, this response occurred independently of actual yeast consumption.

The study revealed that this effect was mediated by olfactory signaling through the odorant receptor co-receptor Orco. Serotonin receptor 2A (5-HT2A) was identified as necessary for yeast odor-induced egg laying, while 5-HT2B had no role in this process. The researchers also investigated whether yeast odor-induced reproductive changes could influence other aspects of the fly's life history.

They confirmed that the odor did shorten the flies' lifespan, but this effect was independent of 5-HT2A signaling, suggesting that the reproductive and longevity responses to food perception are two distinct phenomena.

Further analysis of the brain's neural connections showed that yeast-responsive olfactory neurons specifically target oviposition descending neurons (OviDNs) in the brain. These OviDNs then connect with endocrine-related circuitry in the corpora allata (CA), with the interneurons linking OviDNs to CA neurons being enriched for serotonergic and dopaminergic modulation.

Overall, this research demonstrates that sensory information predicting the availability of food can trigger changes in neural state, ultimately altering reproductive physiology, without the need for actual nutrient acquisition.