MECHANISMS OF SELECTIVE ATTENTION IN GRASSHOPPER CHORUSES - WHO LISTENS TO WHOM

In many rhythmically signaling species of acoustic insects and anurans , males form choruses at typical population densities. Recent findings that females may prefer leading calls indicate that the timing of a m ale's signals relative to those of neighboring choruses is an importan t component of mate attraction. Within a chorus, however, males cannot time their calls such that they lead ail neighbors. Hence, they are e xpected to show selective attention toward only a subset of the group. We used field playback experiments to determine the incidence of and mechanism(s) responsible for selective attention in choruses of the te rritorial grasshoppers Ligurotettix coquilletti and L. planum. Our dat a revealed significant selective attention in both species and are inc onsistent with either fixed-threshold or fixed-number mechanisms. Rath er, regulation of selective,attention by a sliding-threshold mechanism is supported. We discuss these results in the context of the evolutio n of chorus structure.