The evolution of sex differences in mate-attracting signalling Kenji Yoshida and Yoh Iwasa Department of Biology, Faculty of Sciences, Kyushu University, Fukuoka, Japan ABSTRACT Question: To attract mates, many insects dance, have conspicuous plumage, call vocally, and emit signals such as pheromones. Mate-attracting signals are produced predominantly by males in some species and by females in others. We ask, which sex should evolve to produce mate-attracting signals? Method: We used a quantitative genetic model for the signal-sending and signal-receiving efforts of the two sexes. Mate-finding success is assumed to be a product of power functions of the signal sender’s and signal receiver’s investments. Results: If mate-finding success strongly depends on the investments of both senders and receivers, only one sex evolves to send the signals; otherwise, both sexes evolve to emit signals. Males evolve to assume the role that more strongly affects mate-finding success, and to engage in mate-finding activities with more investments than females. Keywords: mate-attracting signal, sex role, elasticity, quantitative genetic dynamics. INTRODUCTION For many insects, the habitats of larvae and pupae are spatially distributed, and adults must find each other to encounter individuals of the opposite sex. Using only random searching, it would be difficult to achieve sufficiently high mate-finding success within a limited time. Many insects send signals to indicate their presence and location to individuals of the opposite sex. Signals may be chemical [i.e. pheromones (Svensson, 1996; Wyatt, 2003; Johansson and Jones, 2007)], auditory [i.e. vocal calls or vibrations (Gwynne, 1987; Cade and Cade, 1992; Cooley, 2001)] or visual [i.e. body and wing coloration, or dance (DeRivera et al., 2003)]. The cost of producing such signals may be enhanced by predators or parasites that use them to identify and locate the senders of the signals, especially signals that can be easily detected (Walker, 1964). Similarly, the cost of searching for the signal sender can be large for the receiver (Lloyd, 1965; Eberhard, 1977; Gwynne, 1987), because it is often laborious to search by flying and walking. Correspondence: Y. Iwasa, Department of Biology, Faculty of Sciences, Kyushu University, Fukuoka 812-8581, Japan. e-mail: yohiwasa@kyudai.jp Consult the copyright statement on the inside front cover for non-commercial copying policies. Evolutionary Ecology Research, 2013, 15: 919–931 © 2013 Yoh Iwasa