ORIGINAL ARTICLE Genetic, spatial, and social relationships among adults in a group of howler monkeys (Alouatta palliata) from Barro Colorado Island, Panama Katharine Milton 1 • David A. Nolin 2 • Kelsey Ellis 3 • Jeffrey Lozier 4 • Brody Sandel 5 • Eileen A. Lacey 6 Received: 15 August 2015 / Accepted: 12 February 2016 / Published online: 2 March 2016 Ó Japan Monkey Centre and Springer Japan 2016 Abstract Kinship plays an important role in the social behavior of many primate species, including patterns of intra-group affiliation and cooperation. Within social groups, kinship is strongly affected by dispersal patterns, with the degree of relatedness among group-mates expec- ted to decrease as the tendency to disperse increases. In primate species characterized by bisexual dispersal, relat- edness among adult group-mates is predicted to be low, with social interactions shaped largely by factors other than kinship. To date, however, few studies have examined the role of kinship in social interactions in bisexually dis- persing species. Accordingly, we collected genetic, spatial and behavioral data on all adult members (three males, six females) in a group of free-ranging mantled howler mon- keys (Alouatta palliata) — a bisexually dispersing species of atelid primate — from Barro Colorado Island (BCI), Panama. Analyses of microsatellite variation revealed that relatedness was greater among adult males in this group (mean pairwise relatedness = 0.32 for males versus 0.09 for females). Relatedness among individuals, however, was not associated with either spatial proximity or frequency of social interactions. Instead, sex was a better predictor of both of these aspects of social behavior. While relatedness among adults had no discernible effect on the intra-group social interactions documented in this study, we postulate that kinship may facilitate affiliative and cooperative behaviors among male group-mates when interacting competitively with neighboring howler groups over access to food or potential mates. Keywords Alouatta palliata Á Bisexual dispersal Á Genetic relatedness Á Spatial associations Á Social network analysis Á QAP Introduction Social interactions are a fundamental component of the lives of group-living primates (Smuts et al. 1987). In many species, kinship among group-mates appears to play a critical role in shaping social behavior, with related indi- viduals being more likely to display affiliative and coop- erative behavior and less likely to engage in agonistic interactions with one another (Hamilton 1964; Greenwood 1980; Hinde 1983; Trivers 1985; Chapais and Berman 2004). Kinship within social groups is strongly affected by dispersal patterns (Melnick and Pearl 1987; Pusey and Packer 1987; Smuts 1987), with the degree of relatedness among individuals expected to decrease as the tendency to disperse increases (Melnick and Hoelzer 1996). Most social mammals, including most primates, are character- ized by male-biased dispersal (Greenwood 1980; Dobson 1982; Pusey and Packer 1987; Clutton-Brock 1989), & Katharine Milton kmilton@berkeley.edu 1 Department of Environmental Science, Policy and Management, University of California, 130 Mulford Hall, Berkeley, CA 94720-3114, USA 2 Department of Anthropology, University of Missouri, Columbia, MO 65211, USA 3 Department of Anthropology, University of Texas, Austin, TX 78705, USA 4 Department of Biological Sciences, University of Alabama, Tuscaloosa, AL 35487, USA 5 Department of Bioscience, Aarhus University, Aarhus, Denmark 6 Department of Integrative Biology, University of California, Berkeley, CA 94720, USA 123 Primates (2016) 57:253–265 DOI 10.1007/s10329-016-0523-5