快猫短视频

In what could be a case of remarkably fast animal evolution, the crickets of Hawaii have begun to purr. The discovery is the latest twist in a decades-long battle between crickets and a parasitic fly that is attracted by their songs.

Male crickets usually sing to attract a mate, but this makes the Pacific field crickets (Teleogryllus oceanicus) on Hawaii easy targets for a parasite. This fly (Ormia ochracea) tracks down crickets by their songs, and deposits its maggots on them. These then burrow inside their host, killing it.

This strong incentive to stop singing meant that by around 1999, crickets on one Hawaiian island 鈥� Kaua鈥檌 鈥� were evolving to stay silent. This was thanks to a mutation that gave males unusually flat wings, which stop them from producing a sound. By 2003, silent males made up about 90 per cent of the population 鈥� one of the that has ever happened in the wild.

Cat-like purr

Similar silencing has been detected on other Hawaiian islands. Researchers discovered, for example, in 2014 that crickets on the island of O鈥檃hu have also evolved flat wings, but via a different genetic mutation. 鈥淚t鈥檚 a really cool rapid convergent evolution story,鈥� says Robin Tinghitella at the University of Denver in Colorado.

But now, some crickets seem to be regaining their voice, and singing in new ways to escape detection by the flies. Studying crickets on the island of Moloka鈥檌, Tinghitella and her colleagues have discovered males exhibiting what she describes as a 鈥�cat-like purr鈥�.

Analysing these crickets in the lab, the team found females are attracted by this call. But from what we know about the parasitic flies, the pitch of the call is probably too low for them to hear.

Rapid adaptation

The team don鈥檛 know yet when the Moloka鈥檌 crickets began to purr. Thinghitella says that all the males she has studied on this island either purr or are silent, so it鈥檚 possible that purring evolved from a silent ancestor. Because silent crickets only started appearing on Hawaiian islands about 20 years ago, the Moloka鈥檌 crickets might have subsequently evolved their purr remarkably rapidly.

Purring may be an ideal solution for the crickets of Hawaii and their parasite problem. While silence is an effective survival strategy, it isn鈥檛 without problems. Mute males find it difficult to attract a mate, and they have to resort to wandering around to find females. Starting to purr might boost males鈥� chances of success.

This depends on how effective the new purring sound is as a mating song. 鈥淚 definitely think it is plausible the purring crickets can communicate with potential mates,鈥� says Ann Hedrick at the University of California Davis. 鈥淭he experiments are convincing.鈥�

Potential for new species

But while females do seem to find this brand-new song attractive, the lab studies revealed that the purr is a bit acoustically messy 鈥� it varies a lot in pitch, for instance. Typically, effective vocal signals evolve to be very specific, with little variation. 鈥淲e鈥檝e caught this trait so early that natural selection doesn鈥檛 seem to have done much to the signal yet,鈥� says Tinghitella.

By choosing to mate with those that purr in a specific way, females may refine this new courtship song in generations to come. 鈥淭he females might whittle it down so that it鈥檚 more like a typical male song, which would be supercool,鈥� says Tinghitella.

Alternatively, the females might learn to love the purr as it is now. It鈥檚 possible that they may become so accustomed to it that they stop finding the original cricket song attractive. If this were to lead to purring crickets no longer breeding with non-purring crickets, it could be a step towards the evolution of an entirely new species.

Tinghitella is determined to reserve a ringside seat to see how this particularly evolutionary game plays out in the years ahead. 鈥淲e鈥檙e going to be spending a lot of time on these islands.鈥�