Bats are prodigious predators of night-flying insects, a fact that figured into the evolution of both the flying mammals and the bugs. Bats developed echolocation, a biosonar system that helps them hunt in the dark, while some insects responded with the ability to hear those ultrasonic echolocation calls and try to evade the hunters. Now a Japanese study suggests that some male moths apparently learned to exploit that predator-prey response as a mating strategy, The Scientist Magazine
|A Yuma myotis hunts a moth in Oregon. Photo © Michael Durham/Minden Pictures, BCI
"The ultrasonic courtship displays of many moth species are believed to have evolved in response to bat echolocation," the magazine said. Researcher Ryo Nakano of the University of Tokyo proposes that when moths evolved ears capable of hearing the ominous hunting calls of bats, that "opened a new line of communication between males and receptive mates," reporter Ed Yong wrote.
The study was published in the journal Scientific Reports
Nakano had previously demonstrated that female Asian corn borer moths basically stop moving and allow mating when they hear a male's courtship song. The reason, according to this new study, is that the female can't distinguish between a male moth's song and a bat's hunting call, The Scientist
said. So the male moths took advantage of the confusion with their "deceptive" courting song.
When Nakano's research team played recordings of a bat's call to captive female moths, the insects responded with evasive maneuvers if they flying. But if not in flight, the females froze in place to avoid detection, Yong reported. When researchers broadcast a male moth's courtship song, females responded the same way – as though facing a bat attack – and the males were able to mate with stationary females.
If neither bat nor moth calls were broadcast and male moths were rendered unable to sing their bat-like song, females resisted attempts to mate, Yong said.
"We were really surprised to female corn borers [mated] when simulated bat calls were broadcast," Nakano told the magazine.
The team found a different response among Japanese lichen moths. Males of this species produce a mating song that females readily distinguish from a bat call, The Scientist
said. Females respond to recorded bat calls, but not to courtship songs, by emitting a series of defensive ultrasonic clicks. Japanese lichen moths, the magazine said, accepted mating when a male courtship song was played, but rejected mating after hearing a bat call.
"Nakano hypothesizes that the initial structure of the moths' sounds determined their evolutionary trajectory," The Scientist
reported. "If the initial sounds were similar to bat calls, they developed into a deceptive courtship song like the call of the corn borer. If those early sounds were distinguishable from bat calls, they developed into an honest song, as is the case with the lichen moth."
Other researchers cautioned that much more research will be required to confirm that evolutionary hypothesis, but Yong notes that Nakano says his team has already started studying this possible scenario among other moth species.