Territoriality and the function of song in the primitive acoustic insect Cyphoderris monstrosa (Orthoptera: Haglidae)

The calls produced by many male insects function both to advertise the singer's location to potential mates and to repel rivals. Cyphoderris monstrosa (Orthoptera: Haglidae) males produce a song that is apparently typical of the acoustic behaviour of other ensiferan insects. The hearing sensitivity of this species does not match the frequency content of male song, however, such that both males and females are relatively insensitive to these signals. Males engage in prolonged territorial disputes that include both acoustic exchanges and overt aggression. The function of C. monstrosa song in territorial interactions between males was examined. The outcome of such interactions was correlated with the relative signalling abilities of the males involved: winning males were more sustained singers than losers. The occurrence of escalated aggression also varied with the males' acoustic behaviour: the winners of interactions in which escalated fights did not occur were stronger singers than the winners of interactions in which there were fights, and strong singers who were muted were still able to win territorial interactions, but faced more vigorous resistance from their opponents. The results demonstrate that the proportion of time spent singing is a true indication of a male's aggressive ability, and that males use this information during territorial interactions. Inter-male communication in this context is thus a function for acoustic signalling, which is not handicapped by limited hearing ability in this species. (C) 1996 The Association for the Study of Animal Behaviour