Brain Cascade Helps Suitor Flies Learn From Rejection


Stephen Luntz

Stephen has a science degree with a major in physics, an arts degree with majors in English Literature and History and Philosophy of Science and a Graduate Diploma in Science Communication.

Freelance Writer


Some fruit flies don't know when to quit, but others do. Now we understand something about what causes the difference. Patricia Chumillas/Shutterstock

No one likes being turned down, and amorous fruit flies are no exception. If a male fly's advances are spurned by a female, he will put less effort into chasing not only her but others as well, suggesting the pain of rejection leaves quite an imprint. A new study has identified the hormones responsible for this behavior and shown that if these hormones are obstructed, males will keep on pushing after rebuffs.

When it comes to romance, human behavior is certainly more complex. However, the findings give scientists investigating human responses to rejection a place to start.


You wouldn't know it from PUA advice channels, but as well as being the decent thing to do, accepting rejection makes evolutionary sense. Despite what movies tell us, the energy we use to pursue uninterested crushes is usually wasted and better spent elsewhere.

Animals that get this message are more likely to win the evolutionary race, and Professor Michael Adams of the University of California, Riverside, is keen to know how these animals learn to give up the chase. Adams identified a brain signaling cascade, connected to courtship memory, where ecdysis-triggering hormone affects juvenile hormone, which in turn alters the behavior of dopamine neurons in the brain. The cascade only operates for three days when the flies are young adults. This is an equivalent timespan to our own teenage years but the cascade's effects last a lifetime.

Lead researcher Sang Soo Lee blocked ecdysis-triggering hormone in flies and found that it turned them into stalkers. “In the absence of the hormonal signaling cascade, the animal doesn’t maintain the memory of courtship failure,” he said in a statement. “It rapidly forgets the unsuccessful courtship, and goes on to court at a level it would have in the absence of that courtship failure.”

No doubt to the relief of female fruit flies, Lee and Adams report in Current Biology that the cascade can be restored. Treatment with methoprene, a chemical that mimics juvenile hormone, turns stalker flies back into their normal selves, which are still pretty bloody annoying.


Sadly, if you're thinking of keeping a spray can of methoprene handy to ward off the sort of people who think it's romantic to play the piano non-stop until you fall in love with them, juvenile hormone is only found in insects. Nevertheless, our thyroid hormone is a good parallel and may have a similar role in human courtship behavior.

It's still unclear why rejected fruit flies put less effort into attracting new females, or whether an imitation of thyroid hormone can be bought in bulk.

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  • fruit flies,

  • brain cascade,

  • juvenile hormone,

  • stalkers,

  • learning circuits