Introduction

Cooperative mating systems require coordinated reproductive efforts among the members of a breeding unit. To achieve coordinated reproduction, cooperative mammalian species commonly possess mechanisms for reproductive and social suppression, limiting the number of reproductive individuals present and establishing a social hierarchy that provides structure for the breeding unit. Cooperative breeding systems are probably formed as a result of two primary factors: (1) ecological conditions that do not favor independent reproduction of subordinate members of the breeding unit, and/or (2) conditions under which the successful production of offspring by a breeding unit requires the effort of an extended family. The proximate factors resulting in philopatry, reproductive suppression, and alloparental behavior by subordinate members of the breeding unit are the topics of this chapter.

The importance of sociality and cooperative behavior to successful reproduction is particularly apparent in “monogamous” mammals, including animals as diverse as prairie voles (Carter, Getz, & Cohen-Parsons 1986; Carter & Getz 1993), Mongolian gerbils (Swanson 1985), elephant shrews (Rathbun 1979), dwarf mongoose (Rood 1980), aardwolves (Richardson 1987), and some New World primates, including marmosets and tamarins (Abbott et al. 1989; Snowdon 1990; Abbott 1993). Monogamy has been characterized by a complex of features including high levels of social behavior and pair bonds, exclusion of strangers from the family, biparental care, reproductive suppression of subordinate members of a family group, incest avoidance, and reduced sexual dimorphism (Kleiman 1977; Dewsbury 1981, 1988; Mendoza & Mason 1986).