A joint study carried out by Danish and Japanese researchers has found that the sensitive ears and avoidance behavior that various species of moths use to avoid bats are also used in communicating about sex.
Moths have probably developed ears for the sole purpose of hearing if their worst enemy, the bat, is near. It has long been thought that moths were dumb, but many of them actually produce sounds - just so softly that bats cannot hear them. The moths use the sounds to communicate sexually. This scientists have known for a few years, and now new research reveals, that moths have developed different ways to not only use their sense of hearing, but also their avoidance behavior that was originally developed as a defense against bats.
"We have examined two different moths and seen that they use their ears and behavior quite differently when they communicate sexually. There is no reason to believe that other moths do not do it in their own way, too. The variation in how to use these skills must be huge", says sensory physiology researcher, Annemarie Surlykke from Department of Biological Sciences, University of Southern Denmark (SDU).
She and her Japanese colleagues from University of Tokyo have studied the two species, Asian corn borer moth (Ostrinia furnacalis
) and Japanese lichen moth (Eilema japonica
). Both species, like many other moths, developed ears to hear the bats, but they have also managed to get more out of their sense of hearing. Males of both species have developed a method to court females with sound - but the methods are very different.
The Asian corn borer moth's technique is the simplest: It produces sounds similar to the echolocation cry of a hunting bat. Thus the male fools the female to believe that a bat is nearby. She responds by sitting perfectly still in an anti-bat freeze position to avoid the bat's attention - and now the male can mate with her, because it is much easier when she sits perfectly still. When the researchers played first the sound of a hunting bat and then the sound of a courting male mating in the laboratory, females responded in both cases by freezing. Females simply could not hear the difference, the researchers conclude.The male Japanese lichen moth is more advanced. He, too, emits a sound that sounds like a hunting bat. But when the researchers played first the sound of the bat and then the sound of a courting male, the females in the laboratory had no doubt: They could hear the difference in the details of the sounds and would only mate if the sound came from a courting male.This means that the evolution of bat defense to sexual communication has gone one step further with the Japanese lichen moth: It has developed a specific recognizable mating signal, while the Asian corn borer moth does not distinguish between sounds from a bat and a courting male.
"The acoustic communication between bats and moths is a textbook example of the interaction between predator and prey. However, our studies show how such a system can evolve, so also moths use their ability to hear and produce sounds to communicate sexually and that they have developed many different ways of doing it. It is a beautiful example of evolutionary diversity", says Annemarie Surlykke.