( Sometimes it pays to be rare—think of ...)Survival of the rarest: Fruit flies shed light on the evolution of behavior

Now, new research suggests that being rare has biological benefits. Professor Marla Sokolowski, a biologist at the University of Toronto Mississauga who in the 1980s discovered that a single gene affects the foraging behaviour of fruit flies, has identified the benefit of rarity in populations of fruit flies with two different versions of the foraging gene. This gene is of particular interest because it is also found in many organisms, including humans. The new study appears in the May 10 issue of the journal Nature.

"There's considerable genetic variation in nature and we haven't been able to explain why it persists, since natural selection ensures that only the best survive," says Sokolowski, who holds a Canada Research Chair in Genetics. "In some cases, individuals with characteristics that differ from the rest of the population are more likely to survive since their rarity makes them less conspicuous to predators. However, to date we haven't understood this type of survival advantage at the level of the gene."

The findings involve a phenomenon known as "negative frequency-dependent selection." Essentially, it suggests that rare variants have a better chance of survival—just as a rare strain of the flu has a better chance of spreading through a population that is already immune to more common strains of the virus. In this case, flies carry one of two versions of the foraging gene (either the "rover" or "sitter" type). Rover larvae move around more than sitter larvae while feeding and they are also more likely to explore new food patches than sitters. The researchers explored the evolutionary mechanism that favours the persistence of both of these types in nature.

Doctoral student Mark Fitzpatrick raised colonies of flies with different ratios of rovers to sitters and different concentrations of nutrients i
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Source:University of Toronto