Cornell biologists shine light on the possible origin of differences in human social behaviors

Male fruit flies don't usually like each other. Socially, they reject their fellow males and zero in on the females they discern via chemical receptors – or so scientists thought.

New research from Cornell University biologists suggests the fruit fly's visual system, not just chemical receptors, are deeply involved with their social behaviors. The work sheds light on the possible origin of differences in human social behaviors, such as those seen in people with bipolar disorder and autism.

The paper, "Visual Feedback Neurons Fine-tune Drosophila Male Courtship via GABA-mediated Inhibition," published in Current Biology on Sept. 5.

Many species of animals use vision to regulate their social behaviors, but the underlying mechanisms are largely unknown. In fruit flies, vision is thought to be used explicitly for motion detection and following, not to regulate social behaviors – but the researchers found that may not be the case.

In our study, we found that hyperactivating the visual system overran the inhibition generated by chemical signals emitted by the male fly to say to the other male, 'Okay, you know, I'm another male, don't mess with me.' Surprisingly, increasing the visual gain in the brain somehow overrides the chemosensory inhibition, attracting male flies to other males."

Nilay Yapici, senior author, assistant professor of neurobiology and behavior

The researchers found that altering the GABARAP/GABA_A receptor signaling in visual feedback neurons in the male brain affected the flies' social inhibitions. When GABARAP is knocked down in the visual system, the males unexpectedly exhibit increased courtship toward other males.

The researchers have found that genes similar to those in the human brain control the fruit fly's visual neurons. Decreasing GABA signaling in the human brain has been associated with social withdrawal characteristics in conditions such as autism and schizophrenia.

"Our results offer a promising avenue for investigating how these proteins regulate social behaviors in the mammalian brain and their potential contribution to human psychiatric conditions," said lead author Yuta Mabuchi, Ph.D. '23.