ANIMAL BEHAVIOUR, 1998, 56, 1091–1098 Article No. ar980871 Females prefer leading males: relative call timing and sexual selection in katydid choruses W. ANDY SNEDDEN & MICHAEL D. GREENFIELD Department of Entomology, University of Kansas (Received 29 December 1997; initial acceptance 28 January 1998; final acceptance 27 February 1998; MS. number: A8009R) ABSTRACT Females of several acoustic insects and anurans have recently been shown to orient preferentially to the leading of two identical male calls presented in close succession. We studied this phenomenon via two-choice phonotaxis trials in the neotropical katydid Neoconocephalus spiza and found that females avoided male calls occurring during an interval beginning immediately after the onset of a leading call. This avoidance occurred whether or not the following call was overlapped by the leader, indicating that the mechanism of preference for leading calls may represent a psychoacoustic precedence effect rather than simple call masking. We also found that females preferred leading calls as long as the amplitude of the following call was not more than 2 dB higher than the leader. Under certain circumstances, preferences for leading calls remained when females were presented with a sequence of four calls. Thus, preferences for leading calls probably influence a male’s attractiveness and mating success in complex natural choruses: females are expected to orient towards males producing leading calls regardless of call length (and the probability of overlapping a following call), when the leading call is up to 1.5 times as distant as a follower, and when succeeded by multiple followers. We suggest that female preferences for leading male calls represent sensory biases that originated in contexts unrelated to sexual selection. None the less they currently play an important role in sexual selection and influence individual male signalling behaviour, and thus chorus structure.  1998 The Association for the Study of Animal Behaviour Males in many species produce conspicuous acoustic signals that function in territorial and sexual advertise- ment. Because females may discriminate between poten- tial mates based on their sexual advertisement signals, many studies have investigated the potential information content of these signals and their role in intersexual selection (see Searcy & Andersson 1986). This research has concentrated on various aspects of spectral, temporal and energy characters of the signal: variation in these signal characters among males, influences of signal char- acters on female mate preferences and phenotypic and genotypic correlations between signal characters and other male attributes (see Ryan & Keddy-Hector 1992; Ryan & Rand 1993; Andersson 1994). In nature, signalling males are often located in close proximity to one another. When close spacing occurs, temporally structured choruses in which neighbouring individuals either alternate or synchronize their calls may result (Greenfield 1994a, b). In these choruses the timing of a male’s calls relative to those of his neighbour(s) may represent an additional signal character critical for female attraction. For example, females in various acoustic insects (e.g. Stiedl 1991; Greenfield & Roizen 1993; Minckley et al 1995; Galliart & Shaw 1996) and anurans (e.g. Dyson & Passmore 1988a; Howard & Palmer 1995; Grafe 1996) prefer leading male calls: given two identical calls presented in close succession, a female usually ori- ents towards the first call. Greenfield & Rozen (1993) and Greenfield et al. (1997) suggest that such preferences are largely responsible for chorus structure: female preference for leading calls selects for males that time their calls such that they most often produce attractive leading signals, and rarely ineffective following calls. The synchronous and alternating choruses observed in nature may emerge as incidental by-products of neighbouring males collec- tively using these timing mechanisms (Greenfield et al. 1997). Several mechanisms might be responsible for a female preference for leading calls. For example, the transition from silence to sound at a call’s onset may be a critical feature of the call’s attractiveness and/or aid localization of its source, and the onset of a following call may simply Correspondence: W. A. Snedden, Department of Entomology, Haworth Hall, University of Kansas, Lawrence, KS, 66045, U.S.A. (email: was@kuhub.cc.ukans.edu). 0003–3472/98/111091+08 $30.00/0  1998 The Association for the Study of Animal Behaviour 1091