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The Callicam
Current Common Marmoset Research

Current Research - Page 8

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III. Biomedical Research (cont.)

D) Reproductive Constraints

  • Subordinate or low ranking male and female marmosets do not reproduce, however, researchers believe it is because of several reasons
  • Subordinate males and females appear not to breed because of the risk of incest and behavioral limitations whereas subordinate females also have hormonal constraints

Common marmosets live in social groups in which all group members help to raise the babies of a single dominant female. In marmoset groups only the dominant male and female breed whereas lower ranking or subordinate marmosets do not because their reproduction is repressed. This suppression of reproduction is the case in many primate and non-primate mammals including yellow baboons. Dominant marmosets, unlike dominants in other species, however, do not appear to use harassment as a means to keep the subordinates from breeding.

Researchers have shown that the ovaries of the subordinate female marmosets are about half the size of the dominant females. Blood samples taken from subordinates to detail hormone levels also revealed that subordinates do not ovulate. When the subordinate females are taken out of the presence of a dominant female and placed on their own they will ovulate. Researchers, therefore, believe that reproductive suppression in subordinate females is due to the hormones of the subordinate female. One hormone believed to be involved is released from the brain and stops the release of hormones stored in reproductive organs. When researchers gave large doses of this hormone to subordinate female marmosets they began to ovulate and when the levels of the hormone were reduced the female stopped ovulating. Researchers believe the lack of this particular hormone has something to do with the reproductive suppression of subordinate female marmosets. Researchers have not pinpointed which cues, visual, behavioral, or olfactory (smell), produced by dominant female marmosets cause subordinates to stop ovulating and, in turn, stop reproducing.

Like the subordinate female common marmosets, subordinate males also do not reproduce. Researchers, therefore, wanted to know the causes of male reproductive suppression. Researchers thought that reproductive suppression of subordinate males was due to cues given by dominant males or as an incest avoidance behavior to keep family members from mating. For the study subordinate males and their fathers were tested either alone or together in a cage and were joined by another female familiar to them (like their mother or mate) or an unrelated and non-familiar female. The number of sexual behaviors the males engaged in was recorded and blood samples were taken to measure hormone levels. Researchers found that the sons engaged in very low rates of sexual behavior with familiar females whereas their fathers (the dominant male) engaged in higher levels. This might imply that the subordinate male does not mate with familiar females because of the chance of being related. When fathers and sons, however, were tested individually with unrelated females, both engaged in approximately the same number of sexual behaviors. This would suggest that subordinate male marmosets have no problem mating if it is with a non-familiar female. Finally, the hormone levels were examined and the researchers found no difference between the levels of fathers and sons. Researchers think that because subordinate male marmosets do not engage in much sexual behavior with familiar females and because hormone levels are similar between dominant and subordinate males that subordinate males are reproductively suppressed to avoid incest.

Researchers now have evidence to believe that subordinate male common marmosets do not reproduce as to avoid incest. Subordinate females, however, are thought to be reproductively suppressed because of hormones. Presently, researchers are still studying the cause of reproductive suppression in male and female common marmosets.

Further Reading:

Abbott, D. H., Saltzman, W., Schultz-Darken, N. J., & Tannenbaum, P. L. (1998). Adaptations to Subordinate Status in Female Marmoset Monkeys. Comparative Biochemistry and Physiology, 119, 261-274.

Abbott, D. H., Saltzman, W., Schultz-Darken, N. J., & Smith, T. E. (1997). Specific Neuroendocrine Mechanismd Not Involving Generalized Stree Mediate Social Regulateion of Female Reproduction in Cooperatively Breeding Marmoset Monkeys. The Integrative Neurobiology of Affiliation, 807, 219-238.

Baker, J. V., Abbott, D. H., & Saltzman, W. (1999). Social Determinants of Reproductive Failure in Male Common Marmosets Housed with their Natal Family. Animal Behaviour, 58,501-513.

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Text by Rebecca Dallwig.