Whether or not a female moth can differentiate between the ultrasonic courtship ‘song’ of a potential mate and the echolocation call made by a bat may depend on her species. The paper, published in Scientific Reports this week, adds new insights into the evolution of deceptive and true sexual communication in moths.
Ultrasonic mating signals in moths are thought to have evolved via the exploitation of a defence mechanism: the sensory bias towards bat echolocation calls. Moths cannot discriminate sound tones, and so the animals must use pulse duration, interval and intensity information to interpret auditory signals. Ryo Nakano and colleagues studied two unrelated species of moths and demonstrate that female Asian corn borer moths cannot distinguish between bat echolocation calls and the ultrasonic courtship songs of would-be mates, whereas female Japanese lichen moths are able to differentiate. In the former species, the male song evokes a bat-avoiding freeze response, which helps the male to achieve copulation - the courtship song is thus deceptive. In the latter species, however, the female recognises her mate by his ‘true’ courtship song.
The study suggests that true and deceptive courtship songs may have evolved from the sounds males happened to emit in a sexual content, which females respectively could and couldn’t distinguish from bat calls.