Some aspects of sexuality and reproduction in groups of captive marmosets (Callitbrix jacchus).

Several aspects of sexual and reproductive behaviour of Callithrix jacchus were studied for almost five years. The most important results are as follows: (1) In artificial groups (AG), heterosexual interactions were observed with varying frequencies between all group members; in the family groups (FG), however only between the parents (a-male and a-female). (2) In general, sexual interactions between two animals in the AG were tolerated by the other group members; in the FG, the offspring tried to disturb all copulations between the parents. (3) Pre- and postcopulatory play, and copulation with intromission and ejaculation are limited to the highest ranking group members. No difference was found between the highest and lower ranking males in the duration of copulation and number of pelvic thrusts. (4) The breeding privilege is correlated with rankorder; that is, only the most dominant male and female reproduce. This gives the impression of a monogamous relationship between the a-animals. (5) Independent of follicle maturation and ovulation, the a-females indicate estrous characterized by a considerable increase in willingness to copulate, associative behaviour between the a-male and the a-female (both most likely influenced or caused by pheromone activity), as well as aggressive behaviour between the a-female and the lower ranking females in the AG. Conflicts between the dominant and lower ranking group members, especially the females in AG, usually cause the group to split. The ability of the lower ranking females to reproduce is adversely affected by the stress to which they are subjected. (6) The parents of the FG are extremely tolerant of their sexually mature adult sons and daughters; expulsion of offspringe by the parents has not occurred as yet in the FG. (7) There is no certain evidence of cyclic visible changes of the genital region or menstrual bleeding in C. jacchus. (8) Captive C. jacchus females breed all year long; gestation is 144--146 days. (9) Homo- and autosexuality is reported for the males of the FG.