Females Remain with Natal Group
KeywordsNatal Group Alarm Caller Inclusive Fitness Howler Monkey Female Philopatry
In most mammalian (social) species, one or both sexes disperse, either to avoid inbreeding or as a result of increased competition for limited resources. The sex that remains in their natal group is considered philopatric, remaining and breeding in their natal range or group (Clutton-Brock and Lukas 2012). The sex that migrates or disperses to another group to find mating partners exhibits natal dispersal – a permanent movement the animal makes from its point of origin to the place where it reproduces or would have reproduced if it survives (Greenwood 1980). If there is migration subsequent to reproduction, we call this breeding dispersal – movement of individuals that have reproduced, between successive breeding sites. Due to the costs of dispersing (see below), typically, individuals only disperse a single time in their lifetime. However, if an animal disperses more than once, they are considered secondary dispersers – permanent or semipermanent movement of breeding adults that have already left their natal group or range (Clutton-Brock and Lukas 2012).
In any social species, one or both sexes typically disperse, while the other remains in their natal group. There has been contentious debate over the causes of dispersal, but primarily animals disperse either to reduce mate and food competition or else to avoid inbreeding. There are numerous benefits to being the philopatric sex or the sex that remains in their own natal group. These center around building and maintaining a detailed spatiotemporal map of food and water resources, threats (predators), and escape routes. Additionally, there are social advantages, namely, gaining support from kin, especially helpful when ascending dominance hierarchies within the group and fending off attacks from rivals (Clutton-Brock and Lukas 2012).
The Costs of Dispersal and Benefits of Philopatry
It is generally accepted that the sex that is most dependent on resources for reproduction (usually females among the mammals) should be philopatric, while the other sex disperses. For example, natal philopatry – at times accompanied by resource sharing from parent to offspring – predicts a kin-structured population and has been argued to represent a precursor for the evolution of sociality. Most social mammals, primates particularly, are characterized by this female philopatry, although examples abound of female transfer (Clutton-Brock 1989; Moore 1984). Some have argued that the direction of sex-biased philopatry is a direct result of the mating system of the species in question (reviewed in Greenwood 1980).
In primates, scientists have historically attempted to decouple philopatry from bondedness (van Schaik 1983) and describe philopatry as an evolved, social response to within and between group competition dynamics, as well as infanticidal avoidance (Sterck et al. 1997). The decision to disperse, however, may be a far more active process. Williams and Rabenold (2005) suggested that in some male corvids, forays into neighboring territories were actually reconnaissance missions to evaluate potential mating opportunities for later dispersal. Accordingly, dispersing carries with it risks, especially for social animals. Resident individuals are often resistant to immigrants or even xenophobic, aggressing at new arrivees; immigrants must also compete with other dispersers, resulting in secondary and even tertiary dispersal attempts (Cheney and Seyfarth 1983). In some species where females disperse (e.g., African lions, meerkats, howler monkeys, prairie dogs), unless immigrating females usurp resident females, dispersers are faced with either founding their own social groups or dying.
In Jim Moore’s (1984) 57-page manifesto on the topic of female transfer, he contextualized the historical significance of our attempts to understand animal (specifically, primate) sociality, beginning with Hamilton’s (1964) work on inclusive fitness and continuing into the early work into matrilineal relatedness in macaques (Macaca sp.) and baboons (Papio sp.). The prevailing view, as Moore noted, was one of stable mammalian groups based on female kin, with exceptions noted throughout the Class (see above). He concluded by saying that “…while kin selection may be a very powerful force among close relatives… for many species it may be relatively weak or even negligible between more distant ones,” and thus the numerous “exceptions” to female philopatry may actually support an earlier description of primate groups as “loosely bound aggregations of individuals which may have little long-term core of kin” (Jolly et al. 1982). That interpretation notwithstanding, we can say that in the vast majority of social mammalian species, and primates specifically, females remain within their natal group, using strong kinship relationships to learn about and exploit their physical and social environment.
- Clutton-Brock, T. H. (1989). Female transfer and inbreeding avoidance in social mammals. Nature. doi:10.1038/337070a0.Google Scholar
- Sterck, E. H. M., Watts, D. P., & van Schaik, C. P. (1997). The evolution of female social relationships in nonhuman primates. Behavioral Ecology and Sociobiology, 41, 291–309.Google Scholar