Sexual Alliances: Evidence and Evolutionary Implications

Abstract

For many species of animals, mating serves more than a procreative function, and much more than gametes are exchanged between partners (Wilson, 1978). Females are expected to be discriminating among males on the basis of a wide variety of properties, including resources that males actually or potentially hold, their abilities as parents, and their genotype (Halliday, 1983; reviewed in Andersson, 1994). In some animal species, particularly internally fertilized insects and vertebrates, aggressive male mating behaviors impose costs on females (Arnqvist, 1995; Campagna, Bisioli, Quintana, Perez, and Vila, 1988; Hiruki et al., 1993b; Le Boeuf and Mesnick, 1991; Smuts and Smuts 1993; Thornhill, 1980; McKinney, Derrickson, and Mineau, 1983) and protection may be a valuable resource that particular males can broker for matings; females that choose to allocate matings to these males effectively exchange sex for protection (Brown-miller, 1975; Mesnick and Le Boeuf, 1991; Smith, 1984b; Trivers, 1985; Wrangham, 1979; Wrangham and Rubenstein, 1986). Alliances with protective males can be an effective female behavior that reduces vulnerability to aggression from other, conspecific males. It also is a factor to consider in explaining (1) patterns of female mate choice and (2) the evolution of a diversity of animal mating systems, including mate guarding, female gregariousness and breeding synchrony, leks, “harems,” monogamy, polygyny, and pair-bonding in humans.