The Washington Post

Silent crickets foil a parasitic fly by using a quick evolutionary trick

The Teleogryllus oceanicus cricket was being targeted by a fly that listened for its chirp. So the males clammed up. (Gerald McCormack/Cook Islands Natural Heritage Trust)

Kauai’s crickets were in trouble. They were being victimized by a parasitic fly that targeted them by listening for their chirps. Once the fly found them, its larvae burrowed inside the crickets and ate them alive.

In the 1990s, nearly a third of the male cricket population on the Hawaiian island had been victimized. But by 2003, the population had rebounded. Why?

A small number of male crickets developed a mutation on the backs of their wings that made them silent. It hobbled their ability to mate but probably saved their lives. It was a classic example of rapid evolution.

But that wasn’t the most dramatic part of the story as recounted by Ed Yong on the Web site of National Geographic magazine. A few years after figuring out what had happened on Kauai, researchers discovered silent crickets on Oahu, where the flies also were targeting crickets.

Since the islands aren’t that far apart, researchers assumed it was the result of the Kauai crickets’ simply breeding with their counterparts on Oahu after crossing the sea by boat or on the wind. But that wasn’t the case.

A female Teleogryllus oceanicus. (Gerald McCormack/Cook Islands Natural Heritage Trust)

The Oahu crickets had developed a different wing mutation. According to a new study led by Sonia Pascoal of Scotland’s University of St Andrews, the crickets are an example of convergent evolution, which occurs when similar organisms develop similar traits independently as a means of adapting to their environment.

The discovery is exciting for researchers because it offers them a still-evolving case they can study in real time rather than years after the fact.

As for those hushed crickets: To compensate for their silence, they cluster around remaining males that can sing.

Lori Aratani writes about how people live, work and play in the D.C. region for The Post’s Transportation and Development team.

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