Genetic Analysis of Group Composition and Breeding System in a Wild Common Marmoset (Callithrix jacchus) Population

We established pedigree relations in three wild common marmoset social groups for which observational data were available, together with genotypes of some individuals from neighboring groups. Relatedness of 40 individuals were based on 11 microsatellite loci amplified from nDNA obtained noninvasively from plucked hair. The wild marmosets were only half as variable as a captive population characterized previously: 2–6 alleles/locus; HO = 0.41 and HE = 0.35. Parentage exclusion probabilities were 61.8% for an offspring and one alleged parent and 90.7% for an offspring with one confirmed and one alleged parent. Each group (n = 5–14 individuals) had two breeding females and ≥2 adult males. Within each group the infants and reproductively inactive adults were closely related to at least the breeding females; the latter were related to each other as closely as mother/infant pairs or sisters. Relatedness of adult males was lower, indicating recent intergroup dispersal. Genetic data confirm Callithrix jacchus live in relatively stable extended family groups of closely related individuals. Matings occurred preferentially among the least related adults and most infants were fathered by the dominant male. The genetic data are consistent with polygynmonandry as are the field observations. Callithrix have variable mating systems, ranging from monogamy to polyandry to polygyny within social groups plus extragroup copulations; our data provide no evidence for polyandry and are inconclusive with respect to extragroup paternity. Nevertheless, noninvasive multilocus genotyping methods will resolve these questions when longer-term studies of entire populations are undertaken.