testosterone in females


Am Nat. 2005 Oct;166 Suppl 4:S85-98.


Testosterone in females: mediator of adaptive traits, constraint on sexual
dimorphism, or both?

Ketterson ED, Nolan V Jr, Sandell M.

Department of Biology and Center for the Integrative Study of Animal
Behavior, Indiana University, Bloomington, Indiana, 47405, USA.

When selection on males and females differs, the sexes may diverge in
phenotype. Hormones serve as a proximate regulator of sex differences by
mediating sex-biased trait expression. To integrate these perspectives, we
consider how suites of traits mediated by the same hormone in both sexes
might respond to selection. In male birds, plasma testosterone (T) varies
seasonally and among species according to mating system. When elevated
experimentally, it is known to enhance some components of fitness and to
decrease others. We report that female T also varies seasonally and
co-varies with male T. Female T is higher in relation to male T in sexually
monomorphic species and is higher absolutely in females of species with
socially monogamous mating systems, which suggests adaptation. We also
consider the effect of experimentally elevated T on females and whether
traits are sensitive to altered T. We hypothesize that sensitive traits
could become subject to selection after a natural change in T and that
traits with opposing fitness consequences in males and females could
constrain dimorphism. Results from birds, including the dark-eyed junco
(Junco hyemalis), reveal many sensitive traits, some of which appear costly
and may help to account for observed levels of sexual dimorphism.

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