Crickets on two Hawaiian islands stopped chirping about 20 years ago -- and scientists embarked on a mission to find out why.
A flatwing cricket that carried on an adaptation that prevents it from making sound but allows it to avoid parasitoids. (Image source: Nathan Bailey)
According to a study published in the latest issue of Current Biology, researchers from Scotland's University of St. Andrews described how male crickets on the islands of Kauai and Oahu lost their song-producing wing structures. Though it was initially thought the crickets might have migrated from one island to another, researchers more recently found they developed the mutation independently.
The inability to produce sound is an adaptation that protects the crickets from parasitoid flies that used to use sound to locate them.
National Geographic explained that people like Marlene Zuk observed the crickets' loss of sound over the last couple decades. By 2003, Zuk didn't hear any more crickets on Kauai.
Scientists now consider the adaptation on the two islands an example of "extremely rapid convergent evolution."
The adaptation in the field crickets (Teleogryllus oceanicus) on Kauai is known as flatwing.
"Flatwing erases sound-producing structures on male forewings. Mutant males cannot sing to attract females, but they are protected from fatal attack by an acoustically orienting parasitoid fly (Ormia ochracea)," the authors wrote.
This type of fly lays its larvae in the crickets, which then kill the insect as they develop.
Just two years after this mutation was spotted in Kauai, it appeared on Oahu as well. There was a difference between the crickets on the two islands though. While the flatwing crickets on Kauai lack all the derived structures, those on Oahu retained a more wild-type wing.
Using genetic analysis, the researchers found that there were distinct markers in flatwing crickets on each island. These different wing morphologies that had the same end result -- an inability to produce -- show "the power of selection to rapidly shape convergent adaptations from distinct genomic starting points," the authors wrote.
"There is more than one way to silence a cricket," Nathan Bailey with the university said. "Evolution by natural selection has produced similar adaptations from different genetic starting points in what appears to be the blink of an eye in evolutionary time.
"This is an exciting opportunity to detect genomic evolution in real time in a wild system, which has usually been quite a challenge, owing to the long timescales over which evolution acts," he added in a statement. "With the crickets, we can act as relatively unobtrusive observers while the drama unfolds in the wild."