| Social grooming is a common form of affiliative behavior in primates. Biological market theory suggests that grooming can be traded either for grooming or other social commodities and services. When no other services are exchanged, grooming is predicted to be approximately reciprocated within a dyad. In contrast, the amount of reciprocal grooming should decrease as other offered services increase. We studied grooming patterns between polygamous male and female in golden snub-nosed monkeys (Rhinopithecus roxellana) from the Qinling Mountains of central China and found that about29.7%of grooming bouts were reciprocated. However, the durations of grooming bouts offered and returned was asymmetrical within dyads. In bisexual dyads, more grooming was initiated by females than males (mean R±SE=-0.27±0.06), which became more pronounced as the number of females per one-male unit increased (rs=-0.85, P<0.05). The rate of copulation per day for each female was positively correlated with the total duration of grooming time females invested in males (rs=0.76, P<0.05). Females without an infant (non-mothers) directed more grooming towards females with an infant (mothers) and were significantly more likely to be non-reciprocated (mean R±SE=0.28±0.02). There was a significant negative relationship between non-mother and mother grooming duration and the rate of infants per female in each one-male unit (rs=-0.62, P<0.05). High-ranking females also received more grooming from low-ranking females than vice versa (mean R±SE=-0.25±0.05). The rate of food-related aggressive interactions was per day for low-ranking females was negatively correlated with the duration of grooming that low-ranking females gave to high-ranking females (rs=-0.71,P<0.05). Our results showed that grooming reciprocation in R. roxellana was discrepancy. This investment-reciprocity rate could be explained by the exchange of other social services in lieu of grooming.We used data of reciprocated grooming bouts among the adult females to test the biological market paradigm partner choice strategies and investigate ’partner control’ strategies such as ’parcelling’ and ’raising the stakes’. Reciprocated grooming bouts data were collected over the course of28months between adult females. Females R. roxellana neither parcelled nor gradually invested more grooming in the bouts. Episode length were significantly different over grooming bouts irrespective of the groomer’s identity and for each of the partners separately. Actually grooming in frequently grooming partners showed that the episodes of a grooming bout were usually longer than that of in infrequent grooming partners at the beginning of the bout and the length of the first episode predicted the whole bout length (rs2=0.912, P<0.001). Moreover, among infrequent groomers the first episode they invested in a grooming bout could not predict the length of the whole bout (rs2=0.276, P=0.074). These results showed that within each dyad every female R. roxellana has a good knowledge of her market value as a grooming partner and knows how much she has to invest to obtain a satisfactory amount of grooming within the same bout. As a tradable commodity grooming value can fluctuate according to both short-term and long-term relationships among all the partners comprising the market.According to a biological market paradigm, trading decisions between partners will be influenced by the current’exchange rate’ of commodities (good and services), which is affected by supply and demand, and the trader’s ability to outbid competitors. In several species of nonhuman primates, newborn infants are attractive to female group members and may become a desired commodity that can be traded for grooming within a biological market place. We investigated whether grooming was interchanged for infant handling in female golden snub-nosed monkeys. Behavioral data were collected over the course of28months on grooming patterns between mothers with infants less than6months old (N=36) and other adult female troop members. Our results provide strong evidence for the interchange of grooming for access to infants. Grooming for infant access was more likely to be initiated by potential handlers (nonmothers)(binomial test:N=756, observed P=0.89, theoretical P=0.5, P<0.001) and less likely reciprocated by mothers (binomial test:N=756, observed P=0.17, theoretical P=1, P<0.001). Moreover, grooming bout duration was inversely related to the number of infants per female present in each one-male unit indicating the possibility of a supply and demand market effect (Coefficient=-0.45, Z=-2.12, N=756, P<0.001). The rank distance between mothers and handlers was negatively influenced grooming duration of nonmother-to-mother grooming bouts that was required before handlers were able to touch or groom infants (Coefficient=-0.57, Z=-0.94, N=756, P=0.017). With increasing infant age, the duration of grooming provided by handlers was shorter suggesting that the ’value’ of older infants had decreased (Coefficient=-0.11, Z=-1.20, N=756, P=0.021). Finally, regardless of the number of infants present, frequent grooming partners were allowed to handle and maintain access to infants longer than infrequent groomers (Coefficient=0.76, Z=2.19, N=756, P<0.001). These results support the contention that grooming and infant handling may be traded in R. roxellana and that the price individuals paid for access to infants fluctuated with supply and demand. |
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