SALTZMAN, W.; PICK, R.R.; SALPER, O.J.; LIEDL, K.J.; ABBOTT, D.H.: Reproductive suppression and reproductive competition in female common marmosets: Effects of an unrelated male

Groups of cooperatively breeding common marmoset monkeys (Callithrix jacchus) often contain only a single dominant, breeding female; subordinate females typically undergo behavioral and physiological suppression of reproduction. However, recent findings indicate that both free-living and captive groups may contain two breeding females. We tested the hypothesis in the laboratory that introduction of an unrelated adult male into a family leads to escape from reproductive suppression by subordinate females, and therefore to the onset of polygyny. We collected hormonal and behavioral data from mothers and daughters housed with their families, before and after the father was removed from the family and either replaced by an unrelated male or immediately returned to the family. Daughters housed in families with unrelated males were significantly more likely to engage in sexual behavior and to conceive than those housed in intact natal families; the latter daughters never engaged in sexual behavior with their fathers and never conceived. However, the two groups of daughters did not differ in their likelihood of undergoing ovulatory cycles. In both groups, daughters ovulated only if they were not behaviorally submissive to their mother. Finally, the emergence of a second breeding female was associated with increased infant mortality, apparently due to infanticide by females. These findings indicate that both rank-related physiological suppression and avoidance of mating with close relatives contribute to reproductive failure in subordinate female marmosets, and that the onset of polygyny is associated with intense competition among females.