Monday, September 25, 2006

More Evolution In Action

This is kind of cool, and since I haven't seen anyone else plugging it, I guess I may as well.

Odd Evolution: Crickets Lose Their Song

In just a few generations, the male crickets on Kauai underwent a drastic genetic change that rendered them incapable of belting out courtship songs, according to a new study.

Typically, male field crickets sport curved wings, and by rubbing a sharp ridge of one wing with a rough part of the other, the cricket produces a mating call

But this serenade also attracts a parasitic fly. Once the insect spots a singing cricket, it deposits larvae onto the cricket. The larvae burrow into the cricket's body, where they mature and subsequently kill the cricket as they emerge from its body.

Good ol' nature. So beneficent.

Researchers led by Marlene Zuk, of the University of California, Riverside, have monitored the crickets on Kauai since 1991. With each visit, the team heard fewer and fewer singing crickets. Then, in 2003 they realized the crickets were abundant but 90 percent of the males had flat wings.

The scientists figure that the quiet mutation protects the crickets from the parasitic fly.

But how do they attract females? Turns out, the flat-winged male crickets have altered their behavior so they can mate successfully. The song-less males rely on the few male crickets with "normal" wings. By congregating around a serenading male, the silent crickets enable females to find and mate with them.

"Instead, the behavior of the flatwings allows them to capitalize on the few callers that remain, and thus escape the fly and still reproduce," Zuk said. "This is seeing evolution at work."

A couple of thoughts: How is it that the cheater males (the ones with the flat wings) aren't getting attacked by flies too? It seems as if congregating would just make it easier to find them. Maybe they're off a little ways, and then they catch the female as she's on her way in. I'm also wondering if we're seeing an equilibrium here between the flat-wing and curved-wing males (what's called frequency-dependent selection) in which case the ratios between the two should remain stable, or if curved-wings will disappear and flat-wings will have to find a new way to attract females. I'm guessing the former. The rarer the cricket songs are, the more rewarding it will be to sing them.