Researchers have found that male fruit flies can learn a new way to use their courtship song after an unusual social encounter.
That fact suggests that the deviation in one of the most studied animals in biology is something that can change in a short time, even if the trait itself is inherited.
Learning fly courtship
Inside the small courtship arena, the men sang to the women whose backward steps followed the sound of the song.
There, neuroscientist Frederic A. Roemschied at the Princeton Neuroscience Institute (PNI) at Princeton University wrote that the altered response changed what male fruit flies learned about courtship itself.
Control males were still exposed to the same light, but only their test partners were exposed to females who retreated in response to singing.
Because the manipulation changed the public impact of the song without silencing it, the result opened up a narrower strategic perspective rather than simply rejecting it.
More than natural intelligence
What changed first was not the song itself but the women’s reaction that followed it.
The researchers used optogenetics, a light-based control of nerve cells, so a man’s pulse can make a person walk backwards in real time.
That was important because men often switch between pulse and sine when the scene changes, exposing them to altered emotions in different situations.
Instead of training a single reflex, the set emphasized how the women’s movements relate to posture and singing.
A new trick
When trained males meet a new female, they begin to sing early during the chase and move away.
Controls usually started next to a slow, almost still partner, which marked a very different opening phase.
That difference reflected a selective change, because the experiments did not show an overall advantage for males to sing.
Experience has changed time and place, two factors that affect whether a song comes across as a target or a proximate influence.
Old measures, new rules
Most of the experimental men also used the usual methods, but they put them in a different way after the strange encounter.
A small group went ahead and used an out-of-control strategy, singing while the flies moved quickly and stayed apart.
That learned movement made sense during training because going backwards would pull the female’s belly into a good mating position.
Once the cue disappeared, the same choice became less beneficial, which helps explain why the effect didn’t last.
Memories that fade
At the beginning of the test, the learned trick was most evident during the first ten minutes with the inactive woman.
In hindsight it looked like controls, suggesting that common sense quickly pushes men into default behavior.
During training, the sine wave appeared alone less than 10% of the time, leaving the pulse wave as the main cause.
That fact is important because the experiment taught men a lot about the pulse track, which is related to the altered movement of women.
The brain is being scanned
The rapid loss of this behavior suggests plasticity, a temporary reversal of neural responses to experience.
One person is dopamine, a brain chemical associated with learning, because courtship-related learning in flies is now dependent on it.
Another possibility is the cells that detect and initiate songs that help males judge location, movement and the best time to sing.
Those goals remain unproven, but the short term limits the search to cycles that can improve in a few minutes.
Reward and risk
Walking backwards probably didn’t send a single clean message to a man’s brain during courtship.
When the female moved, the reaction could feel discouraging, but on the other hand it could bring her closer.
That combination helps to explain why men were more likely to date each other instead of shutting down, contrary to the usual denial-based theory.
Instead of teaching avoidance, the phenomenological interaction taught a brief and very clear strategy development.
Learning without new songs
The male flies did not create a new sound, so the finding separates learning from the physical action itself.
Instead, they demonstrated learning through use, the evolution of a built-in brand after social experience.
Few animals are known to learn to communicate, so this is a narrow range of importance.
Fruit flies now provide a way to test that idea in detail, with genes and circuits that scientists can manipulate.
Where this is going
This method works best for long records, because estimating a change strategy on the fly requires a lot of behavior.
A follow-up project has already secured more than 400,000 euros over two years to push the question deeper.
Roemschied said: “Now we can try to control social experiences and examine how behavior corresponds to these experiences.
Despite that limitation, a settee can try to see, smell, touch, or behave in a mate to teach new social rules.
Small worms, big light
These experiments show that even a small brain can change a person’s inherited courtship rules after only a brief encounter.
This makes fruit flies a better model for studying how social experience is linked to behavior, and when that adaptation breaks down.
The study was published by Current Biology.
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