Scientists revealed today that a prolific parasite is helping shape the destiny of a species it does not even infect. The complex relationship between the parasite, its host, and the unconnected species is the first known example of evolutionary pressure from such a remote source.

Five years ago, University of Rochester scientists linked the bacterial parasite, Wolbachia, to the separation of a single wasp species into two distinct species. Now, researchers have found that this same parasite in fruit flies is not only meddling with the sexual behavior of its host, but may be causing a change in the sexual behavior of a species that is not infected.

"Darwin's model of evolution is based on genetic variation that causes differences in survival and reproduction," says John Jaenike, professor of biology. "However, this apparently simple scheme can operate in very complex and indirect ways."

Several years ago, Jaenike found that two very closely related species of fly differed in that one was thoroughly infected with Wolbachia while the other was Wolbachia-free. Each species resided in coniferous forests on opposite sides of North America, and, knowing that Wolbachia can affect reproductive isolation between species, he wondered whether the two species actually met each other in nature. A stretch of forest in Canada physically connected the eastern and western communities, so he set out to discover whether these two species' territories overlapped.

In June of 2002, Jaenike sent two under-graduate students on a summer-long camping trip across the northern United States and Canada. Armed only with nets, store-bought mushrooms, and Fed Ex boxes, Chad Cornish and Paul Gibas camped at designated spots, set out the mushrooms, collected the flies that gathered on them, and mailed them back to Rochester.

"On the whole it went off without a hitch, except one package was held up in customs and we received a big box of dead flies," says Jaenike. As the
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Contact: Jonathan Sherwood
jonathan.sherwood@rochester.edu
585-273-4726
University of Rochester
9-Oct-2006