Behav Ecol Sociobiol (2005) 59: 191–197 DOI 10.1007/s00265-005-0024-9 ORIGINAL ARTICLE Ole-Gunnar Støen · Eva Bellemain · Solve Sæbø · Jon E. Swenson Kin-related spatial structure in brown bears Ursus arctos Received: 10 January 2005 / Revised: 12 May 2005 / Accepted: 2 June 2005 / Published online: 2 August 2005 C  Springer-Verlag 2005 Abstract Kin-related social structure may influence re- productive success and survival and, hence, the dynamics of populations. It has been documented in many gregarious animal populations, but few solitary species. Using molecular methods and field data we tested: (1) whether kin-related spatial structure exists in the brown bear (Ursus arctos), which is a solitary carnivore, (2) whether home ranges of adult female kin overlap more than those of nonkin, and (3) whether multigenerational matrilinear assemblages, i.e., aggregated related females, are formed. Pairwise genetic relatedness between adult (5 years and older) female dyads declined significantly with geographic distance, whereas this was not the case for male–male dyads or opposite sex dyads. The amount of overlap of multiannual home ranges was positively associated with relatedness among adult females. This structure within matrilines is probably due to kin recognition. Plotting of multiannual home-range centers of adult females revealed formation of two types of matrilines, matrilinear assem- Communicated by C. Nunn O.-G. Støen () · J. E. Swenson Department of Ecology and Natural Resource Management, Norwegian University of Life Sciences, P.O. Box 5003, NO-1432 ˚ As, Norway e-mail: ole.stoen@umb.no Tel.: +47-64-96-58-00 Fax: +47-64-96-58-01 E. Bellemain Laboratoire d’Ecologie Alpine (LECA), G´ enomique des Populations et Biodiversit´ e, Universit´ e Joseph Fourier, CNRS UMR 5553, BP 53, F-38041 Grenoble Cedex 9, France S. Sæbø Department of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, P.O. Box 5003 NO-1432 ˚ As, Norway J. E. Swenson Norwegian Institute for Nature Research, Tungasletta 2, N-7485 Trondheim, Norway blages exclusively using an area and dispersed matrilines spread over larger geographic areas. The variation in matrilinear structure might be due to differences in com- petitive abilities among females and habitat limitations. The influence of kin-related spatial structure on inclusive fitness needs to be clarified in solitary mammals. Keywords Dispersal . Genetic distance . Matriline . Social structure . Philopatry Introduction Kin-related social structures have been documented in many animal populations (Clutton-Brock et al. 1982; Gompper and Wayne 1996; Ishibashi et al. 1997). A kin- related social structure in females may influence reproduc- tive success and survival and, hence, population dynamics, as demonstrated in microtines (Lambin and Krebs 1993). Matrilines, defined as individuals descending from the same ancestral female, have been found to be functional demographic entities in animal populations (Johannesen et al. 2000). Studies of kin-related social structures in mam- mals have been restricted mostly to group-living species (Smuts et al. 1987; Gompper and Wayne 1996). The recent development of highly polymorphic molecular markers has provided the potential to study social structure in solitary species that, due to their elusive nature, would otherwise be difficult to study (e.g., for carnivores, see Waser et al. 1994; Schenk et al. 1998; Ratnayeke et al. 2002). The brown bear (Ursus arctos) is a solitary carnivore with a promiscuous mating system (Schwartz et al. 2003). Males have larger home ranges than females, but both males and females have home ranges that overlap intra- and inter- sexually (Dahle and Swenson 2003a). Dispersal is sex- biased, with highly philopatric females establishing their breeding home ranges in or adjacent to their natal areas and males generally dispersing from their mothers’ home ranges (Glenn and Miller 1980; Blanchard and Knight 1991; McLellan and Hovey 2001; Proctor et al. 2004).