Researchers from The Universities of Manchester and Birmingham have identified the exact nerve cells in the brain that drive important behavioural changes in female fruit flies after they mate.
The discovery, published in the journal eLife today (insert date), sheds light on how animals integrate sensory information to guide reproduction and has, say the researchers, general implications on understanding the brains' role in reproduction.
When male fruit flies mate, they transfer a molecule called sex peptide (SP) to the female.
This molecule triggers two key changes: females reject courting males who want to mate again, and they lay more eggs.
Although scientists have known about SP for years, until now the precise neurons in the female nervous system that respond have remained a mystery.
The findings suggest that the brain allows females to fine‑tune their responses to mating depending on their internal state and environmental conditions - helping them maximise the chances of reproductive success.
Lead author, Dr Mohanakarthik Nallasivan, from the University of Birmingham said: "Reproductive behaviours are hardwired in the brain, rather than learned. So if we can understand this behavioural pathway, we may be able to influence it.
"Knowing the exact nerve cells that drive key behavioural changes in female fruit flies after they mate is a very important step along that path.
"This knowledge could, for example, help develop methods to restrict the ability of malaria carrying female Anopheles mosquitoes to mate, which precedes the blood-meal."
Study-lead Prof Matthias Soller from The University of Manchester added: "The fruit fly was the first organism with a fully sequenced genome. Now, in 2022, it is the first brain to have all its neurons catalogued and synaptic connections mapped".
"We now have the resources available to learn how behaviour is encoded in the brain and influenced by decision making processes".
"This pioneering work has implications for increasing our understanding of how our own brains work, particularly those behaviours that are 'hard wired', or built into our neural circuitry."
To identify the neurons, the research team attached the sex peptide pheromone, that normally circulates in the insects' blood after mating, to the cell-membrane on the outside of neurons.
When such membrane-tethered sex-peptide is expressed in the same nerve cell as its receptor, post-mating behaviours will be triggered.
To understand how the brain responds to the sex peptide, the scientists explored the complex genetic framework of key reproductive genes involved in sex determination, resulting in male or female offspring.
By combining genetic tools that mark a handful of neurons controlled by reproductive genes, the scientists identified two distinct sets of interneurons - one in the brain and one in the abdominal nerve centre - that regulate the behaviours.
The approach allowed them to pinpoint the neurons that detect the sex peptide, which they named Sex Peptide Response‑Inducing Neurons (SPRINz).
Further mapping of the neural circuits showed that SPRINz receive signals from sensory‑processing neurons and send outputs along two separate pathways.
Artificially activating SPRINz in the brain induced post‑mating behaviours, effectively mimicking a command. This demonstrates that sex‑peptide‑responsive neurons act as central hubs, integrating sensory cues and coordinating the female's behavioural decisions after mating.
