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Dryad

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

Abstract

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.