Change of tune for Hawaiian crickets?

Hawaiian cricket

After years of attracting females through song, Hawaiian field crickets have gradually silenced. But evolutionary processes could mean that they discover a new voice.

10 May 2019 by Sarah McDaid

Crickets that lost their song in an evolutionary bid to escape predators could hold the key to understanding how bursts of new species can form so quickly.

Male crickets sing to attract females by rubbing their wings together. Unfortunately, for field crickets in Hawaii, their song also attracts female flies. These flies squirt larvae onto male crickets which burrow into, consume and ultimately kill the cricket.

In 2003, scientists noticed that the male crickets were becoming silent - rapidly adapting to the threat of death by fly. Silent males had lost the structures on their wings that they normally rub together to produce song that attracts females.

Dr Nathan Bailey, a NERC-funded evolutionary biologist from the University of St Andrews has studied the crickets for 13 years and noticed something intriguing about silent males' wings.

Dr Bailey said:

Songless males move their wings. They go through the motions like a violinist who's lost his bow but keeps trying to play anyway. But even though the wing structures that vibrate and produce sound have been erased, it's not a complete erasure. Silent cricket wings contain the reduced, distorted remains of sound-producing structures.

Those functionless wing remnants piqued Dr Bailey's interest. In a recent NERC-funded study, he and his collaborators Sonia Pascoal and Fernando Montealegre-Z wanted to find out if these wing structures could eventually re-evolve as new sound-producing organs, with the crickets rediscovering their voice.

The team made genetic crosses to see just how different the wing structures were, and then measured acoustic resonances of the silent wings - akin to plucking the violinist's strings without a bow, but on a tiny, precise scale. This bit of detective work enabled Dr Bailey to work out what Hawaiian crickets might sound like if they ever re-evolved the ability to sing.

He said:

There was an astonishing amount of variation in silent crickets' wings. Different wings could potentially make sounds across a far more variable range than this species normally sings.

It would be like losing the violin from an orchestra, but getting a new cello, bass, viola, maybe even a banjo waiting in the wings.

Dr Bailey said it was "hard to say" whether these hidden signals will re-evolve someday and drive the evolution of new cricket species with different songs:

Song is an important driver of speciation in insects, and it has been evolutionarily lost on numerous occasions across the cricket family tree. What we've shown is that such losses could potentially lead to greater species diversity in the long run if conditions are right.

Biologists often study past patterns of diversification, but it is important to consider future evolutionary potential - silent Hawaiian crickets have shown us a neat way to do that.

'Testing the role of trait reversal in evolutionary diversification using song loss in wild crickets' - Nathan W Bailey, Sonia Pascoal and Fernando Montealegre-Z, 2019, Proceedings of the National Academy of Sciences of the United States of America (PNAS).