This is a study of sexual development and differentiation in the marmoset monkey, Callithrix acchus acchus. The effects of perinatal steroid treatments on the anatomy, physiology and behaviour of females of various mammalian species are reviewed. A summary of the literature on marmoset development is included. Detailed measurements of growth, plasma sex hormone levels and reproductive behaviour were obtained from captive marmosets at birth until 600-1000 days of age. Body weights and knee-to-heel lengths were similar for both sexes. Males had high levels of testosterone from 5-100 days of age and testosterone began to rise again, coincident with the pubertal growth of the testis, at about 250 days. Pre-ovulatory levels of oestradiol were found in females of 200 days old and over, but ovulations, as indicated by high progesterone levels (*N 20 ng/ml), did not occur for nearly another 200 days. The majority of males and females were copulating by 100-500 days old. Males of this age could ejaculate spermatozoa and females were able to conceive. However, first conceptions occurred more frequently when males and females were 500-600 days of age. Maternal age and experience was found more important than paternal for rearing offspring. In all captive groups only the dominant female reproduced. In families, sexual behaviour was virtually limited to the parents, but their maturing daughters ovulated and their sons could ejaculate spermatozoa. In newly-formed peer groups of unrelated animals, clear rank orders were achieved by fighting. The dominant male and female ranked over all the others, formed a pair bond, and attempted to prevent any other sexual relationship. Older and heavier males held high rank, but no such correlation was found with females. Subordinate females copulated but stopped ovulating. There was some evidence of accompanying elevated prolactin levels. The fertility of subordinate males was less affected because they copulated and could ejaculate spermatozoa. The mechanisms of reproductive inhibition and their possible roles in the marmoset's monogamous social system are discussed. Neonatally androgenized female marmosets displayed enhanced rough-and-tumble play and masculine sexual behaviour, but without the loss of feminine behaviour. There was no effect on aggression or fertility, but the clitoris of each animal was permanently hypertrophied. Other primates, such as the rhesus monkey and the human, may have a period of neonatal behavioural differentiation, but the function of high testosterone levels in newborn males remains to be determined. The differentiation of marmoset behaviour after birth may partly explain why females born co-twin to males are chimeric but are otherwise normal.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:640112 |
| Date | January 1979 |
| Creators | Abbott, David Howard |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/11120 |
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