Female fruit flies only need 15 minutes to process the sights, smell, sounds, and touch that determine “Mr. Right.”
Researchers have discovered the neural circuitry that allows females to make this decision. They report in PLOS Biology the first-ever map of the brain circuits involved.
This mapping let the scientists identify the single gene responsible for the network and the neurotransmitter that mediates the “yes” or “no” response—and confirm a 50-year-old hypothesis on decision-making.
A female’s choice of mate is a key factor in the survival or evolution of a species. She is deciding which traits will be passed on to the next generation.
“It’s a complex decision,” says senior author Rui Sousa-Neves, a research professor in the genetics and genomic sciences department at Case Western Reserve University, who led the research.
During courtship, “the female fruit fly is listening to love songs from the male and taking in the color of his eyes, how he dances and smells, and she’s getting cues from the way he touches her abdomen,” he says.
Scientists have been working with fruit flies for more than 100 years. The University of Tennessee’s Benjamin Hochman isolated mutations on the fly’s fourth chromosome, a tiny chromosome compared to its three others, more than 40 years ago.
But the resource sat on a shelf because no one could link mutations to genes, Sousa-Neves says.
To link the mutation to a gene, Sousa-Neves previously developed a series of tools to molecularly map it and more recently developed a method to generate mutant neurons using a fluorescent color code.
They showed that the gene datilografo (dati), a transcription factor, is essential to organizing and maintaining the neural circuitry in the central brain that lets a female accept a mate.
The gene is required in an excitatory circuit involving just a few neurons in the olfactory lobe, the first entry point for odor processing in the brain. The neurons express acetylcholine as their neurotransmitter.
In addition, dati is required in two other brain centers: a region where olfaction and other senses are integrated, as well as a novel region.
Monitoring females that were being courted “provides the first evidence for a hypothesis made 50 years ago,” Sousa-Neves says. “To make decisions we don’t balance all options like a computer does. . . . Here females made decisions based on a sum of stimuli that came from outside.”
Further testing showed that if they removed the dati gene, female flies made no decisions and never accepted to mate with males.
Do we decide quickly, too?
“Genes similar to dati are not only found in flies,” says Sousa-Neves. “It’s a conserved gene present in marine arthropods to humans.”
Does the gene play the same role in humans? Do humans actually make such a decision in 15 minutes?
“Nobody knows,” Sousa-Neves says. Finding the answers will take time.
But, now that they’ve discovered the players involved, “it opens up investigating decision-making at a brand new level,” he says.
The researchers are looking further into how dati establishes the circuits for decision-making in flies and what decision-making involves.
Source: Case Western Reserve University