Gut bacteria change the sexual preference of fruit flies

To work out why, Sharon repeated Dodd’s experiment with the fly Drosophila melanogaster, and raised two strains on either molasses or starch. After just two generations, she found the same effect that Dodd did: the flies were more attracted to individuals reared on the same diets. Something in their food was changing their behaviour.

Bacteria in our guts change according to the food that we eat, so Sharon suspected that something similar was happening in the flies. This idea was dramatically confirmed when he gave the insects a dose of antibiotics. Immediately, their sexual bias disappeared and they were just as likely to mate with flies from either group.