Behavioural evidence for monopolization of paternity in multi-male groups of golden lion tamarins

Abstract. Recent reviews of field data on marmosets and tamarins (Callitrichidae) conclude that wild callitrichids exhibit a variable breeding system with a high incidence of cooperative polyandry, contrasting with the long-held supposition of monogamy for this Neotropical primate family. In this study on a wild population of golden lion tamarins, Leontopithecus rosalia, approximately 40% of groups contained two non-natal adult males. Both males cared for infants and, in some groups, both males copulated with the reproductive female. However, there was evidence for a dominant/subordinate relationship between males in most groups. Ovulation was probably not concealed, and dominant males were responsible for almost all sexual behaviour when females were likely to be fertile. A demographic model indicated that a currently non-reproductive subordinate male that waited for the dominant male in his group to die or for a breeding vacancy in an adjacent group could expect higher lifetime reproductive success than a male that left a subordinate position in search of breeding opportunities elsewhere. Thus, the observed stability of two-male groups does not require non-zero certainty of paternity for the subordinate male. A polyandrous group structure is common in this population, but paternity is probably monopolized by a single dominant male in most groups.