152,000 cousins in fly’s ‘family bush’

IOWA STATE (US) —Talk about extended families: Houseflies have more than 152,000 relatives—and those are just the ones that researchers know about.

“It really isn’t a tree, it’s sort of a bush,” says Gregory Courtney, professor of entomology at Iowa State University. “Because of this, and because the history of flies extends more than 260 million years, it’s difficult figuring out the relationships between this branch and that branch.”

The problem with tracking fly evolution is that every so often, a species of fly will branch into two different species, and then those two will split again, and again and again.

If a series of these branches or dichotomous splits occurs over a brief period of time, a rapid radiation of new flies and an evolutionary tree that looks more like a bush is the result. At least three episodes of this rapid radiation have occurred in the history of flies, Courtney says.

“[The fly family tree] probably involves dichotomous splits,” says Courtney. “But we can’t always resolve these when there are lots of dichotomous splits going on at the same time.”

“One of the nice results of this research was confirmation that a number of episodic radiations may have occurred. That explains some of the difficulty we’ve had in resolving relationships of different types of flies,” he says.

The new research, published in the journal Proceedings of the National Academy of Sciences, finds that a group of flies called mountain midges (Deuterophlebia) is the oldest group of flies and is positioned near the base of the fly family tree.

“Morphology is just one piece of information that we use to try to figure out relationships,” he says. “We looked at a whole suite of morphological characteristics—about 400 characteristics for this analysis.”

From its beginning, the fly family tree has been continuously evolving. There are now more than 152,000 species of flies that have been described and named, and least that many more haven’t yet been discovered and described.

Brian Wiegmann of North Carolina State University, Raleigh, headed the study that was funded by the National Science Foundation.

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