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Genetics study illuminates aspect of war between the sexes: Fruit fly edition

Drosophila erecta is an African fruit fly with a big problem: The male sexual organ is so rough that sex acts, almost literally, as a two-edged sword — necessary for reproduction, but physically injurious.

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Amir Yassin analyzed how evolution could simultaneously favor two different colors for females. Photo by John Pool.

Because evolution places reproduction as first among equals, females have developed overlapping solutions to their dilemma. First, as Amir Yassin, a scientist in the University of Wisconsin–Madison Laboratory of Genetics recently discovered, females have evolved protective armor plates in their reproductive tract.

But “females still have an incentive to avoid excess mating attempts beyond what they need to reproduce,” observes John Pool, senior author of a paper published this week in the journal Nature Communications.

And that explains the second solution: a “cross-dressing” strategy that colors many females as dark as males, reducing the amount of injurious male attention.

However, Pool, an assistant professor in the Department of Genetics, says the ruse only works if some females retain the distinctive lighter color. “By resembling males, the darker females are successful at hiding from males, but that only works if there are other, lighter females.”

Having established that optimum reproduction “demands” females of both colors, Pool and his colleagues homed in on a well-known pigment gene called “tan” that creates the color on the exoskeleton, as they focused on how the genetic controls could deal with such a contradictory need.

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Some female Drosophila erecta fruit flies have a dark coloration that camouflages them as males, reducing the number of copulations and, therefore, the amount of injury. Photo by Amir Yassin.
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Assistant professor of genetics John Pool collects fruit flies in Ethiopia and other parts of Africa (such as here above a cherry farm in South Africa). Photo by Amanda Pool.

“We localized the trait difference to a particular sequence that regulates how much tan is turned on, and we concluded that both versions of this regulatory sequence have been in existence for several million years. This supports the idea that natural selection has kept this difference around because it has such strong survival value,” Pool explains.

NOTE: The full UW-Madison news release about this work highlights a second project by Pool. Read about it here: http://news.wisc.edu/study-illuminates-war-between-the-sexes-fruit-fly-edition/#sthash.wFkG3zYo.dpuf.

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