Evolution of deceptive and true courtship songs in moths

Abstract

Ultrasonic mating signals in moths are argued to have evolved via exploitation of the receivers' sensory bias towards bat echolocation calls. We have demonstrated that female moths of the Asian corn borer are unable to distinguish between the male courtship song and bat calls. Females react to both the male song and bat calls by “freezing”, which males take advantage of in mating (deceptive courtship song). In contrast, females of the Japanese lichen moth are able to distinguish between the male song and bat calls by the structure of the sounds; females emit warning clicks against bats, but accept males (true courtship song). Here, we propose a hypothesis that deceptive and true signals evolved independently from slightly different precursory sounds; deceptive/true courtship songs in moths evolved from the sounds males incidentally emitted in a sexual context, which females could not/could distinguish, respectively, from bat calls.

Evolutionary escalation: the bat–moth arms race

“…Although we will not describe this additional function of sound production in detail, we mention it here because we believe it is an interesting extension of the bat-moth story. For example, males of the pyralid moth Ostrinia furnacalis produce sounds to elicit an anti-bat response (freezing) so they can forcibly mate with perched females, whereas females of the arctiid moth Eilema japonica can distinguish between bat and male calls and only take defensive action to bat calls (Nakano et al, 2013). Producing sounds for mating purposes also comes at the potential cost of attracting eavesdropping bats, as is seen in the pyralid moth Achroia grisella (Alem et al, 2011).…”

“…Generally considered rare in moths, acoustic communication for mating has been discovered in more and more moth species in recent years, suggesting that it is far more common than previously appreciated, but was previously overlooked in some species because of the low intensity of the signals (Nakano et al, 2008(Nakano et al, , 2009). For reviews of intraspecific acoustic communication in moths, see Conner (1999) and Nakano et al (2015).…”

“…Most adaptations that make bats better moth hunters also make them more effective hunters of other insects, and such adaptations are therefore not moth specific. Likewise, some moths use their ears to detect not only bats but also insect-eating birds or mates (Conner, 1999;Nakano et al, 2015).…”

Simple ears – flexible behavior: Information processing in the moth auditory pathway

“…In moths, three distinct categories of intraspecific ultrasonic signals have been identified: (i) calling songs for mate attraction (Heller and Krahe, 1994;Surlykke and Gogala, 1986;Gwynne and Edwards, 1986;Spangler et al, 1984, Heller andAchmann, 1993b;Jang and Greenfield, 1996), (ii) courtship songs for mate recognition/acceptance (Nakano et al, 2008;Spangler, 1988;Simmons and Conner, 1996;Trematerra and Pavan, 1995;Kindl et al, 2011;Nakano et al, 2013, Sanderford and Conner, 1995, Sanderford et al, 1998, and (iii) territorial calls (Bailey, 1978;Alcock and Bailey, 1995). In addition, it should be mentioned that many other moth species produce ultrasound, though the function is often still unknown (Heller and Achmann, 1993a;Skals and Surlykke, 1999;Kay, 1969).…”

Double meaning of courtship song in a moth

“…By contrast, in other species with the true courtship song, such as the tiger and lichen moths (Noctuoidea, Arctiidae), females assume a mate-acceptance posture as a positive response to a male producing courtship song [7,10,[14][15][16][17]27]. Unlike the corn borer, females of, for example, the Japanese lichen moth, Eilema japonica, do not show bat-avoidance responses to male courtship songs but do show evasive behaviour against bat echolocation calls; females develop mate preferences for male songs [7]. Male courtship songs in these species work inversely to one another-a negative or positive function.…”