Crickets Fall Silent to Stay Alive
The Hawaiian island Kauai. Crickets on the island have evolved an inability to sing to protect themselves from parasitic flies. (Credit: Christopher Michel)
Evolution has left crickets on two Hawaiian islands with the inability to sing, protecting them from a deadly threat, according to a new study published in the journal Current Biology.
Male crickets normally chirp to attract mates, but on the islands of Kauai and Oahu, their songs can also draw parasitic flies, which are extremely effective at following cricket songs. Females typically seek out male crickets on which they lay their eggs. Once the eggs hatch, the maggots burrow inside the crickets and devour them from the inside out. In the early 90s, researchers at the University of St. Andrews in the United Kingdom discovered 30 percent of male crickets in Kauai were infested with fly larvae, causing the population to decline dramatically over the next decade.
But the crickets found a way to survive — silence. The islands’ crickets acquired a mutation that eliminates the ability of males to chirp. Crickets sing by rubbing their wings together, but the mutation produces flat wings in male crickets that lack the fine structures necessary for making sound.
The types of cricket wings found on Kauai and Oahu. Normal male wings have fine structures that emit a chirping sound when rubbed together. The flat wings found on crickets in Kauai and Oahu are physically and genetically different from each other, but both leave males mute. (Credit: Nathan Bailey)
These silent crickets evade the parasitic flies and pass on their mutation to future generations. By 2003, the cricket population on Kauai had rebounded, and nine of every ten males on the island had flat wings.
Two years later, the silent crickets were discovered on the island Oahu. At first, scientists didn’t think there was anything unusual about this simultaneous appearance. The two Hawaiian islands are located less than 100 miles apart, and boats traveling between the two islands could have carried Kauai crickets to the new breeding ground.
But according to the new study, the wings of silent crickets on the two islands are actually different. Both types of wings leave males without the ability to sing, but their distinct appearances provided the first clue that the two populations developed their wings independently. Scientists began to suspect that they were looking at convergent evolution — facing the same threat, two cricket populations independently evolved a similar trait.
An oceanic field cricket (Teleogryllus oceanicus) conceals itself from predators. Evolution of these crickets is happening rapidly. (Credit: G. McCormack, Bishopmuseum.org)
Genetic tests revealed even bigger differences between the crickets. The scientists traced the flattened wings on both islands to single, sex-linked genes. Each population also had distinct genetic markers, again strongly suggesting that flattened wings on both islands evolved independently of each other.
The speed that the mutation spread across the island is particularly remarkable. Crickets only live for a few weeks, and silent males dominated populations after less than 20 generations — the blink of an eye on an evolutionary time scale. “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,” said Nathan Bailey, a biology researcher at St Andrews University in the UK and corresponding author of the study, in a recent press release. “With the crickets, we can act as relatively unobtrusive observers while the drama unfolds in the wild.”
Sources:
Study in Current Biology, 2014 Press Release, 2006 Press Release, 2006 study in Biology Letters, Rapid evolution
This article was originally published at The Wildlife Society, June 3, 2014.