Market effects offset the reciprocation of grooming in free-ranging redfronted lemurs, Eulemur fulvus rufusMethodsRedfronted LemursStudy Population and Data CollectionData AnalysesResultsGrooming Reciprocity within BoutsGrooming Reciprocity, Aggression and Trader ClassMale-male dyadsFemale-male dyadsFemale-female dyadsDiscussionGrooming and Social PowerAlternative ExplanationsConclusionsAcknowledgmentsReferencesMarket effects offset the reciprocation of grooming in free-rangingredfronted lemurs, Eulemur fulvus rufusMarkus Porta,b,*, Dagmar Clougha,b, Peter M. Kappelera,baDepartment of Behavioral Ecology and Sociobiology, German Primate CenterbDepartment of Sociobiology/Anthropology, University of Go¨ttingenarticle infoArticle history:Received 21 May 20 08Initial acceptance 2 July 2008Final acceptance 29 August 2008Published online 30 October 2008MS. number: 08-00337Keywords:aggressionbiological marketEulemur fulvus rufusgroomingreciprocal altruismredfronted lemurSocial grooming is a commonly observed affiliative behaviour in primates. Grooming has been suggestedto represent a service in a biological marketplace, exchanged either for grooming or for other socialcommodities or services. Accordingly, grooming is predicted to be approximately reciprocated withina dyad when no other services are being exchanged, but it should be more asymmetrical if partners havedifferent quantities of other services to offer. We analysed 412 grooming bouts observed in four groups offree-ranging redfronted lemurs to test this prediction. Grooming in this species seems to take place ina highly reciprocal manner because partners usually alternate in the roles of groomer and gromee withina grooming bout. However, within dyads there were asymmetries in the duration of grooming given andreceived. In both sexes, more grooming was directed from low-ranking towards high-ranking individualsthan vice versa, and in males this asymmetry became more pronounced as the number of subordinatesper group increased. Grooming in bisexual dyads was generally skewed in favour of males, but patternsof grooming between the sexes were less clear than within the sexes. In addition, aggression occurred athigh frequencies between classes of individuals that were characterized by nonreciprocal grooming,suggesting that grooming may serve as a means to reduce aggression in dyads with a high potential forconflicts. Taken together, our results indicate that a strict reciprocation of grooming can be offset bypower differentials between partners, where grooming appears to be traded by subordinates in exchangefor the tolerance of dominants.Ó 2008 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All ri ghts reserved.Cleaning another individual’s fur (allogrooming, hereaftergrooming) constitutes a common form of affiliative behaviour inprimates (Sparks 1967; Goosen 1987), and has also been observedin a number of other mammalian species (e.g. impalas, AepyceropsMelampus: Hart & Hart 1992; wood mice, Apodemus sylvaticus:Stopka & Macdonald 1999; meerkats, Suricata suricatta: Kutsukake& Clutton-Brock 2006). Grooming is beneficial for the recipient asdirt and ectoparasites are removed (Hutchins & Barash 1976; Bar-ton 1985); yet this behaviour is likely to be associated with costs forthe individual performing it, for example, in the form of decreasedvigilance (Maestripieri 1993; Mooring & Hart 1995) or decreasedtime available for other activities (Dunbar 1992; Henzi et al. 1997).It has therefore been suggested that grooming represents a form ofaltruism (Seyfarth & Cheney 1984).Across primate species, many grooming interactions take placeamong relatives (Schino 2001), where altruism can be attributed tokin selection (Hamilton 1964). However, grooming also occursamong nonkin. Altruism among nonkin is assumed to be favouredby natural selection if the altruist later receives a significant benefitfrom the recipient of the initial altruistic act (reciprocal altruism:Trivers 1971). It has therefore been suggested that grooming withinpairs of individuals should be reciprocated over time, or exchangedfor other beneficial acts (Hemelrijk & Ek 1991). Because the firsttheoretical model to predict grooming relationships in primatesconsidered grooming to be the means by which individuals main-tain social bonds (Seyfarth 1977), much emphasis concerning aninterchange with other forms of altruism has traditionally been laidon support in conflicts (e.g. Seyfarth & Cheney 1984; Hemelrijk1994). However, whereas several studies revealed that groomingitself is usually reciprocated (e.g. Hemelrijk & Ek 1991; Leinfelderet al. 2001; Ventura et al. 2006), evidence suggesting an exchangefor coalitionary support is rare (Henzi & Barrett 1999; but seeSchino 2007 for a recent meta-analysis).Henzi & Barrett (1999) extended the traditional reciprocalaltruism approach of social grooming by attributing a more flexiblefunction to this behaviour. Following biological market theory (Noe¨& Hammerstein 1995), they proposed that grooming representsa service in a biological marketplace, which can be exchanged forgrooming (reciprocated) or for other services or commodities in themarket. Accordingly, grooming is predicted to be reciprocated indyads where no other services are being exchanged, but to be*Correspondence: M. Port, Department of Behavioral Ecology and Sociobiology,German Primate Center, Kellnerweg 4, 37077 Go¨ttingen, Germany.E-mail address: [email protected] (M. Port).Contents lists available at ScienceDirectAnimal Behaviourjournal homepage: www.elsevier.com/locate/yanbe0003-3472/$38.00 Ó 2008 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.doi:10.1016/j.anbehav.2008.08.032Animal Behaviour 77 (2009) 29–36asymmetrical if it is traded as a commodity to obtain a differentservice from the partner. Coalitionary support represents only onepossible service; further services or commodities are, for instance,tolerance (Kapsalis & Berman 1996; Kutsukake & Clutton-Brock20 06), food (de Waal 1997) or matings (Gumert 2007a). Thus,individuals can be divided into different trader classes, dependingon what they have to offer. The concept of trader classes has foundwide application within the biological market framework, not onlyin the study of grooming behaviour or other forms of intraspecificcooperation, but also in interspecific mutualism (Noe¨20 01). Theexchange of commodities between