AbstractIn pair-living mammals, genetic monogamy is extremely rare. One possible reason is that in socially monogamous animals, mate choice can be severely constrained, generating a risk of inbreeding or incompatibility between partners. To escape these constraints and minimize inbreeding, individuals might engage in extra-pair copulations. Alternatively, inbreeding can be avoided by natal dispersal. However, little is known about the interactions between mating system, mate choice and dispersal in pair-living mammals. Here we show that coppery titi monkeys (Plecturocebus cupreus), are mostly genetically monogamous, as parentage analyses indicated no cases of extra-pair paternity. We did not find evidence for relatedness- or heterozygosity-based mate choice. Despite the lack of evidence for active inbreeding avoidance via mate choice, mating partners were on average not related. We further found that dispersal was opportunistic, with both sexes dispersing over varying distances. Our findings indicate that even opportunistic dispersal, as long as it is not constrained, can generate sufficient genetic diversity to prevent inbreeding. This, in turn, can render both active inbreeding avoidance via mate choice and extra-pair copulations unnecessary, thus helping to maintain genetic monogamy.Key wordsGenetic monogamy, mate choice, dispersal, titi monkeys, Plecturocebus