CHORUS STRUCTURE IN TARBUSH GRASSHOPPERS - INHIBITION, SELECTIVE PHONORESPONSE AND SIGNAL COMPETITION

In species where sexually advertising males signal in groups, the timi ng of an individual's signals relative to those of neighbours may be a critical aspect of mating success. Temporal signal interactions and t heir relation to female attraction were examined in the tarbush grassh opper, Ligurotettix planum. The acoustic signals of neighbouring L. pl anum males form a crudely alternating chorus. Alternation within male pairs is effected by an (inhibitory resetting) mechanism that causes a male to refrain from calling for at least a 1.8-s interval beginning 0.2 s after the onset of a neighbour's call. This mechanism is not equ ally applied to all neighbours. Rather, males are selectively inhibite d by only their nearest one or two neighbours, whereas more distant, b ut audible, callers are ignored. Males also time their calls to occur shortly before calls at the ends of predictably recurring silent inter vals. Consequently, males do not decrease their calling rates in high population density, and they compete effectively for females. Phonotax is in L. planum females is characterized by preference for leading cal ls, a psychoacoustic feature that would select for timing mechanisms t hat avert the production of following calls in males. The inhibitory r esetting mechanism averts such calls. Moreover, because males are only inhibited by nearest neighbours, their strongest competitors, they ca n avoid producing unattractive following calls and still maintain norm al calling rates. By calling at the ends of silent intervals, males ma y actively compete with neighbours via 'attempting' to relegate the ne ighbours' calls to ineffective, from the neighbour's perspective, time intervals following the focal male's call. (C) 1995 The Association f or the Study of Animal Behaviour