Sexual Signalling in an Artiicial Population: When Does the Handicap Principle Work? 1 Sexual Signalling and the Handicap Principle

Males may use sexual displays to signal their quality to females ; the handicap principle provides a mechanism that could enforce honesty in such cases. Iwasa et al. 1] model the signalling of inherited male quality, and distinguish between three variants of the handicap principle: pure epistasis, conditional, and revealing. They argue that only the second and third will work. An evolutionary simulation is presented in which all three variants function under certain conditions; the assumptions made by Iwasa et al. are questioned. Sexual selection is a distinct subset of natural selection. The idea is that evolution is an exam with two papers: in order to reproduce, an animal must not only survive to adulthood, but, in a sexual species, it must gain mating opportunities with members of the opposite sex. One of Darwin's insights was that selection for sexual attractiveness and selection for survival could exert opposing evolutionary pressures. If, for some reason, females came to prefer males with elaborate and costly ornaments, such as the peacock's tail, then sexual selection would push towards yet more costly ornaments, because males with longer tails experience greater mating success. At the same time, natural selection would push for less costly ones, because males with longer tails are more vulnerable to predation and less likely to survive to adulthood. An early explanation for extreme male ornament traits and female preferences was that an initial, random bias led to linkage between trait and preference genes and that a runaway cycle of exaggeration then took place 2]. Another possibility, more recently explored, is that male ornaments function as \indicator mechanisms", i.e., that they are used by males to signal their quality as mating partners to females 3]. This paper describes an evolutionary simulation, based on a population-genetic model by Iwasa et al. 1], that explores the conditions under which this kind of sexual signalling could evolve. The suggestion that male ornaments are signals of mate-quality leads to a problem in understanding how honest signalling could be maintained. Why should low-quality males ever honestly signal their condition, when by doing so they will make themselves unlikely to be chosen as mates? Why wouldn't all