Organizational effects of testosterone on the number of mating partners and reproductive success in females of a social rodent

The timing of exposure to testosterone produces activational and
organizational effects in vertebrates. In females, high serum testosterone
levels, and the exposure to high testosterone levels during early
development, are negatively associated with female fertility and
attractiveness to males. We tested these hypotheses by examining
associations between serum testosterone levels (an indirect index of
activational effects), anogenital distance (AGD, a direct index of
organizational effects), and the number of male mating partners attained
by females, and the number of offspring weaned. We examined 525 wild degu
(Octodon degus) females across an 11-year study. During the mating season,
we found no association between female serum testosterone levels and AGD,
the number of male mating partners, or with the number of offspring
weaned. However, we found that the number of male mating partners was
positively associated with the number of offspring weaned, suggesting that
females obtain direct fitness benefits from polyandrous mating. During the
nursing season, we recorded a positive association between female AGD and
the number of offspring weaned. This indicates that testosterone
organizational effects had a positive effect on female fertility. This
finding is unique within the theoretical framework of female phenotypical
masculinization via intrauterine position phenomenon.