RECENT RESEARCH FINDINGS

Testosterone Reflects Social Status and Group Composition

Relation to male competition in sifaka and vervets

In the "challenge hypothesis," John Wingfield has argued that the highest levels of testosterone in birds serve primarily to support mate defense. Serum testosterone has been shown to reflect aggression in nonhuman primates, but its relation to mating access is less clear. In Old World monkeys like baboons and macaques, testosterone generally does not reflect male rank, but a more predictable relationship may occur in species where there is an alpha male who is markedly higher in rank than the other group males and often has exclusive mating access to females. 

In Madagascan sifaka, we found that fecal testosterone was significantly higher in the alpha male of the group than in the other group males. Loss of dominant status and peripheralization were associated with marked reductions in testosterone.  Although sifaka generally experience  testicular regression after breeding, testosterone levels were maintained during an attempted immigration.

In a survey of vervet monkeys from four different populations in Kenya, we found that only one male per group maintained breeding season levels of serum testosterone levels after the close of the mating season.  Testosterone levels of these males were significantly correlated with the number of females within the group but not with the number of resident males, suggesting that alpha males may maintain testosterone secretion after breeding in order to defend resident females against extra-group males. 

D.K. Brockman, P.L. Whitten, A.F. Richard, and A. Schneider 1998 Reproduction in freeranging male Propithecus verreauxi: The hormonal correlates of mating and aggression. American Journal of Physical Anthropology 105:137-151.

P.L. Whitten, T.R. Turner, C.J. Jolly 1998 Ecogeographical variation in testosterone: a primate test of the challenge hypothesis. American Journal of Physical Anthropology Supplement.

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