Post-partum changes in hormones and sexual behaviour in captive groups of marmosets ( Callithrix jacchus)

Abstract

Video-tape recordings were made of behavioural interactions in eight family groups of marmosets for 24–30 days after parturition. Blood samples were collected from females for measurement of plasma luteinizing hormone (LH) and progesterone. A pre-ovulatory LH surge occurred in six females between days 10–18 (mean±sem, 13.8±1.3 days). In these groups, sexual interactions increased in frequency during the post-partum period and males began to initiate mounts on days 1, 2, 2, 6, 8 and 10 respectively. Mount and ejaculation frequencies increased significantly during the peri-ovulatory phase as compared to the pre-ovulatory phase and females were more proceptive and receptive than in the early post-partum period. Peri-ovulatory increases in sexual activity were more pronounced in 3 groups in which females had failed to conceive. In the remaining 3 groups, sexual interactions tended to continue at higher levels into the post-ovulatory phase when the females were pregnant. In captive marmoset groups, copulatory behaviour during the post-partum period is stimulated by changes in non-behavioural cues from the female (increased sexual attractiveness to the male) as well as by changes in her behaviour (proceptivity, receptivity) which vary in importance between individuals.