Sexual Selection and the Evolution of Copulatory Behavior in Nocturnal Prosimians

Abstract

The simplistic view of nocturnal prosimians as “solitary” primates leading impoverished social lives is now known to be incorrect. Although many prosimians are relatively nongregarious, they occupy varied and complex social networks which are maintained by means of olfactory and vocal signals, as well as by direct encounters during nocturnal activities (Charles-Dominique, 1977; Schilling, 1979; Bearder, 1986). Bearder has defined five types of social organization among the nocturnal primates, all of which involve varying degrees of home range overlap and range size differentials between the sexes (Figure 1). Mating systems may differ from social systems, however, as has been amply demonstrated by fieldwork on diurnal anthropoid species. Examples include the existence of monogamy and polyandry in some callitrichids (Sussman and Garber, 1987; Goldizen, 1987), and multi-male influxes into one male units in Erythrocebus patas and in various Cercopithecus species (Cords, 1986; 1988). Since, in some nocturnal prosimians, the home ranges of a number of females may overlap that of a single male (e.g., in Perodicticus potto: Type 2 system in Figure 1), it is tempting to speculate that the male may monopolize sexual access to these females, producing something akin to a polygynous “one-male group”. However, this review will present evidence that sperm competition (Parker, 1970) and sexual selection by female choice (Eberhard, 1985) have influenced the evolution of the genitalia and copulatory behavior in males of many nocturnal prosimian species. It will be argued that many of these animals have “dispersed” mating systems in which females are able to mate with a number of males during the peri-ovulatory phase of the ovarian cycle.