Mate recognition in duetting species: the role of male and female vibrational signals

In sexual communication, partners often form a duet, an exchange of species- and sex-specific signals, and in such systems mate recognition is likely to be reciprocal. We studied the role of vibrational signals in reproductive isolation in the genus Aphrodes (Hemiptera: Cicadellidae) in which mate recognition is based on highly divergent male advertisement calls and similar female replies. We first determined in playback experiments the preferences of females of four Aphrodes species to conspecific and heterospecific male advertisement calls as well as to species-specific elements in these calls. Females of all four species responded preferentially to calls of conspecific males; however, male calls composed of similar elements played only a limited role in mate recognition. In particular, females of Aphrodes aestuarina and Aphrodes bicincta showed higher responsiveness to each other's male calls than to calls of other species. In this species pair we further examined the role of female signals and duet structure in assortative mating using ‘no-choice’ mating experiments. The generally higher responsiveness of A. aestuarina females to male calls of A. bicincta did not translate into higher mating success in this heterospecific cross; lengthy replies of A. aestuarina females resulted in a breakdown of a complex species-specific duet structure and associated difficulties in locating the female reduced the probability of heterospecific mating. Our study shows that in mating systems based on a duet, males may contribute more than females to sexual isolation between species. Males' contribution to assortative mating may stem not only from mate recognition but also from inability to locate the source of the heterospecific female reply.