Species Recognition Influences Female Mate Preferences in the Common European Grasshopper (Chorthippus biguttulus Linnaeus, 1758)

Mate-choice preferences are responsible for the evolution of some of the most fascinating and conspicuous secondary sexual signals. Their evolution is generally explained by hypotheses assuming direct or indirect benefits of mate choice such as: (i) Fisherian self-reinforcement processes, (ii) indicator mechanisms (good genes hypothesis), or (iii) direct phenotypic benefits (for explanations, see e.g. Andersson 1994). However, these hypotheses mask the fact that other processes can influence mate-choice preferences. Preferences could evolve as pleiotropic effects of other selection pressures on sensory systems (Ryan 1998); e.g. they could be shaped by species-recognition processes (Ryan 1990; Ryan et al. 1990). Sexual selection can be a driving force in reproductive isolation and enhance speciation (Dobzhansky 1937; Panhuis et al. 2001; Kirkpatrick & Ravigne 2002; Svensson et al. 2006). However, the avoidance of heterospecific matings also has the potential to shape the properties of signals and receivers in mate recognition systems (Pfennig 1998; Hankison & Morris 2002; Ryan et al. 2003; Phelps et al. 2006). Corroborating this argument, a theoretical study by Ryan & Getz (2000) showed that species recognition can drive intraspecific sexual selection. Heterospecific matings often result in offspring with reduced fitness or no offspring, and thus an increase in the efficiency in mate-choice recognition and a simultaneous avoidance of heterospecific matings should enhance the fitness of an individual (e.g. Shapiro 2000; Rice & Chippindale 2002). Classically, it is thought that if a sex prefers traits that best allow species recognition, then it should prefer those that are most typical for its own species. In other words, it should prefer intermediate values around the population mean (Butlin et al. 1985). Such trait characteristics should vary little within and between individuals and represent the ‘static’ properties of a trait (Gerhardt 1991). According to this argument, species recognition leads to stabilizing selection Correspondence K. Reinhold, Evolutionary Biology, University of Bielefeld, Morgenbreede 45, D-33615 Bielefeld, Germany. E-mail: klaus.reinhold@ uni-bielefeld.de