Abstract
Allogrooming in primates has acquired an important social function beyond its original hygienic function and can be exchanged either for itself or used as a currency to obtain other benefits such as copulations, access to infants or agonistic support. We explore the strategic use of grooming as a social tool in semi-wild golden snub-nosed monkeys (Rhinopithecus roxellana) in central China, a species where two desirable resources, viz. reproductive males and infants, are restricted to the mating and birth season, respectively. We predict that females expend their grooming selectively to different individuals according to their “value”. Our results show that in the mating season, females devoted more grooming to the resident male than in the birth season, and this effect was particularly strong in non-mothers (females without newborn infants). Moreover, females were more likely to groom the resident male after copulation than during baseline social conditions. In the birth season, females devoted more grooming to other females than in the mating season, and mothers (females with newborn infants) were the most valuable grooming partners. The mean rate of contact by non-mothers toward infants of other females was significantly higher after grooming the mothers than in baseline social conditions. In conclusion, our findings lend credence to the notion that primate females use grooming as a strategic tool to obtain limited resources such as males and infants and vary preference for particular individuals depending on the seasonal availability of valuable resources.
Highlights
IntroductionAllogrooming (grooming hereafter) is probably the most common affiliative behavior among non-human primates and may serve multiple functions [1]
Allogrooming is probably the most common affiliative behavior among non-human primates and may serve multiple functions [1]
Primate affiliation, including allogrooming, can occur both between relatives and non-relatives [25]; while altruism among relatives is usually attributed to kin selection [26,27], altruism involving non-relatives can be a form of reciprocal altruism which assumes that the altruist later receives a significant benefit from the recipient of the initial altruistic act [28]
Summary
Allogrooming (grooming hereafter) is probably the most common affiliative behavior among non-human primates and may serve multiple functions [1]. Grooming has likely evolved originally for a hygienic function [2,3], and has been coopted for derived social purposes [4], including tension reduction [5,6], tolerance around resources [7], alliance formation and dominance acquisition [8,9], and group cohesion [10]. In non-human primates that breed year-round, desired resources such as infants and ‘reproductive males’ can become available at any time of the year, depending on individual female reproductive state. These resources are available only during a short time window and are limited and should elicit competition. Competition over access to males is expected to be further exacerbated in social units containing only a single adult male [29]. Seasonal fluctuations in supply of valuable resources are expected to produce asymmetries in efforts to acquire those resources (i.e. how frequently do females groom the male vs. other females)
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