Female-female aggression and male indifference in response to unfamiliar intruders in lion tamarins

The role of intolerance toward unfamiliar conspecifics in promoting exclusivity of mating and preferential association among breeding pairs was examined in captive golden lion tamarins, Leontopithecus rosalia. In their home cage, resident breeding pairs were presented with an intruder that varied in sex and age (adult or subadult). Resident female tamarins directed high levels of attack, agonistic displays, and approaches toward subadult and adult female intruders. Male residents, in contrast, showed virtually no attack responses to intruders of any sex-age class, and showed only moderate levels of agonistic displays in the presence of adult male intruders. Attacks and threats by resident females were associated with the number of subadult helpers present in the social group: females in groups with more helpers present exhibited higher levels of aggression to intruders. The results suggest that female intolerance of conspecifics may be important in the regulation of sociosexual relationships in breeding pairs, and that female-female reproductive competition is particularly extreme in this species.