Testicular function, secondary sexual development, and social status in male mandrills (Mandrillus sphinx)

doi:10.1016/0031-9384(92)90370-H

Physiology & Behavior

Volume 52, Issue 5, November 1992, Pages 909-916

https://doi.org/10.1016/0031-9384(92)90370-H Get rights and content

Abstract

Positive correlations between dominance rank and plasma testosterone levels have been described for adult males of several primate species in captivity, but the relevance of such observations to free-ranging animals is unclear. CIRMF in Gabon maintains a breeding group of 45 mandrills in a six hectare, naturally rainforested enclosure. This study describes correlations between dominance rank (in agonistic encounters), levels of plasma testosterone, testicular volume, body weight, and development of secondary sexual characteristics (red and blue sexual skin on the muzzle and rump areas) in male mandrills under semifree ranging conditions. Two morphological and social variants of adult male mandrill were identified. Large-rumped or fatted adult males (n = 3) remained in the social group and exhibited maximal development of sexual skin coloration as well as large testicular size and highest plasma testosterone levels. By contrast, slimmer-rumped or nonfatted males (n = 3) lived a peripheral or solitary existence and these exhibited less development of their secondary sexual coloration and had smaller testes and lower plasma testosterone levels. Longitudinal studies of gonadal development in these six males revealed that testicular volumes and plasma testosterone levels increased most rapidly during pubertal development (4–5 years of age) in the three animals which proceeded to the fatted condition. These included the highest ranking, group-associated male which exhibited the most intense sexual skin coloration and had higher testosterone levels, although this was not correlated with testicular volume. This study shows that in the male mandrill social factors and reproductive development are interrelated. Physical features characterising dominant, group-associated males are subject to more rapid pubertal development, and circulating testosterone levels are higher in such individuals both during puberty and in adulthood.

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Two semifree-ranging mandrill groups, inhabiting large, naturally rainforested enclosures in Gabon, were studied to measure morphological, endocrine, and behavioral changes that occurred when adult males rose, or fell, in dominance rank. Gaining alpha rank (N = 4 males) resulted in increased testicular size and circulating testosterone, reddening of the sexual skin on the face and genitalia, and heightened secretion from the sternal cutaneous gland. Blue sexual skin coloration was unaffected. New alpha males increased in rump “fattedness,” but not in body mass, and spent more time associated with other group members, rather than ranging alone. Loss of alpha position (N = 4 males) resulted in less pronounced effects than those that occurred after males had risen to alpha positions. Deposed alpha males showed decreased testicular volume, decreased body mass, a reduction in the extent of red (but not blue) sexual skin coloration, and decreased sternal gland activity. Deposed males did not decrease in the brightness of sex skin coloration. These results demonstrate that male–male competition and rank reversals have remarkable effects upon testicular function, secondary sexual traits, and behavior in the adult male mandrill. Secondary sexual traits respond to changes in male social status and therefore may be important as intrasexual signals of dominance rank.
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ArticleTesticular function, secondary sexual development, and social status in male mandrills (Mandrillus sphinx)

Abstract

Access through your organization

Anim. Behav.

Horm. Behav.

Anim. Behav.

Gen. Comp. Endocrinol.

Behavioral and physiological suppression of fertility in subordinate marmoset monkeys

Am. J. Primatol.

Ecology and behaviour of nocturnal primates

The descent of man and selection in relation to sex

Male social rank and reproductive success in wild long-tailed macaques

The effects of testosterone on the sexual skin and genitalia of the male talapoin monkey

J. Reprod. Fertil.

Observations on sexual development in male orang-utans (Pongo pygmaeus)

Int. Zoo Yrbk.

Squirrel monkey reproduction: The “fatted” male phenomenon and seasonal spermatogenesis

Science

Social influences on estrogen excretion and ovarian cyclicity in saddle-back tamarins (Saguinus fuscicollis)

Am. J. Primatol.

The mandrill in Gabon's rain forest—ecology, distribution and status

Oryx

Preliminary report on the grouping of mandrills (Mandrillus sphinx) in Cameroon

Primates

Article
Testicular function, secondary sexual development, and social status in male mandrills (Mandrillus sphinx)