Swingers: The Life of the Research Fruit Fly

Fruit flies must get excited when they're selected for research roles. The life of a research fruit fly mimics that of a college student. Scientists encourage fruit flies to drink copious amounts of alcohol—and now they're encouraging the flies to hook up with lots of other flies.

Biologists have wondered why female species from insects to mammals tend to have multiple mates even though polyandry is more dangerous for the female. It turns out that polyandrous behavior in females prevents extinction.

Researchers at University of Exeter and University of Liverpool reared several groups of fruit flies. In one case, the fruit flies could mate normally, allowing the females to have multiple partners. In other situations, the researchers limited the population so females only had one beau. The scientists followed the fruit flies for 15 generations (in case you're wondering, a fruit fly has a very short lifespan). Of the 12 monogamous populations, five became extinct because of males dying out from sex-ratio distortion (SR) chromosome, which causes the male sperm to be killed before fertilization. In families where females only have one mate, the female offspring are more likely to pass on the SR onto their sons, lessening the chance of the brood's survival. The study says that having multiple mates prevents the development and spread of the SR chromosome.