The Silence of the Crickets

“For most of us, crickets are probably most recognizable by the distinctive chirping sounds males make with their wings to lure females. But some crickets living on the islands of Hawaii have effectively lost their instruments and don’t make their music anymore. Now researchers report in the Cell Press journal Current Biology on May 29 (Pascoal et al.: “Rapid Convergent Evolution in Wild Crickets”) that crickets living on different islands quieted their wings in different ways at almost the same time” (source):

“There is more than one way to silence a cricket,” says Nathan Bailey of the University of St Andrews. “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.” In the Hawaiian crickets, silence arose amongst males as a way to hide from parasitoid flies that are attracted to male song. Fly larvae burrow into crickets, killing them within a week’s time. Quiet crickets avoid those deadly flies and still manage to mate by positioning themselves near males in the population that do sing, Bailey explains.

At first, Bailey and his colleagues thought that silent flatwing crickets had arisen just once and subsequently migrated from one island to another. However, when they looked closely at the wings of crickets on the island of Kauai versus the island of Oahu, they noticed obvious differences in the crickets’ forms.

Further experiments in the lab showed that the silent wings in both cricket populations could be traced to single, sex-linked genes. However, Sonia Pascoal, a postdoc in Bailey’s laboratory, performed a genome-wide scan that showed that the genes responsible are linked to different genetic markers. Remarkably, the same trait arose at about the same time on two islands, but independently and in different underlying ways.

That makes the crickets a remarkable example of convergent evolution, the researchers say, and there is still a lot more to learn from them. Bailey’s laboratory is now working to unravel the genes and developmental pathways involved, as well as their interactions with the rest of the cricket genome. “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,” Bailey adds. “With the crickets, we can act as relatively unobtrusive observers while the drama unfolds in the wild.”

Image 1 for article titled "The Silence of the Crickets"
Teleogryllus oceanicus, commonly known as the Australian, Pacific, or oceanic field cricket, is a cricket found across Oceania. T. oceanicus populations in Hawaii arose through human-assisted introduction. In 2003, a novel mutation was identified in the highly parasitized Teleogryllus oceanicus population in Kauai that resulted in a wing morphology that renders the male obligately silent (known as flatwing). This mutation is inherited through a single sex-linked allele. With such a heavy parasite presence, males with the mutation could have a survival advantage, which led to rapid evolution, with over 90% of males exhibiting the flatwing morphology after less than 20 generations. While these males were at an advantage when it came to survival, they were also at a disadvantage when it came to reproduction because they were unable to sing to attract a mate (Wikipedia: Teleogryllus oceanicus)

Image 2 for article titled "The Silence of the Crickets"
The map shows Hawaiian islands on which flatwing males are found and the year they were first documented. Although several flatwing males have recently been found on the “Big Island,” Hawaii, the lab population derived from that island was established prior to 2012 and did not contain flatwing males at the time (from the Current Biology article)