Data from: Masculinized females produce heavier offspring in a group living rodent

Summary: Alternative morphotypes have been reported less frequently in females than in males. An exception to this rule is the gradient of phenotypical masculinization reported in some female mammals, in which feminized and masculinized females represent two opposite ends along this gradient. These phenotypical differences originate during prenatal development as the consequence of maternal effects. Feminized and masculinized females differ in several traits, including morphological, physiological, behavioral, and reproductive traits. Differences previously reported in reproductive traits between feminized and masculinized females come mostly from mechanistic studies performed in the laboratory, and not necessarily on social species. As a result, it is unclear to what extent these reported differences between female alternative morphotypes materialize in wild, natural populations. We quantified the effect of female alternative morphotype on female reproductive traits in a natural population of Octodon degus, a highly social rodent. We assessed female alternative morphotype through a continuous gradient of anogenital distance. Thus, feminized females were close to the short end of anogenital distance, while masculinized females were close to the long end of this gradient. We also tested the hypothesis that the social environment interacts with female morphotype to influence female reproductive traits.
In female degus, only body weight affected litter size, where heavier females weaned more offspring. Masculinized females delivered male-biased litters and weaned heavier offspring. Lastly, masculinized females gave birth later in the breeding season compared to feminized females.
Contrary to previous claims, our findings do not support that masculinized females are less fertile than feminized females. Moreover, masculinized females produced heavier, potentially higher quality offspring compared with feminized females.

研究摘要：相较于雄性，雌性的替代形态（alternative morphotypes）的报道频率更低。这一规律的例外情况见于部分雌性哺乳动物中报道的表型雄性化梯度（phenotypical masculinization），其中雌性化雌性与雄性化雌性分别处于该梯度的两个极端。此类表型差异起源于产前发育阶段的母体效应。雌性化与雄性化雌性在形态学、生理学、行为学及繁殖相关性状等多个维度存在差异。此前关于两类雌性繁殖性状差异的研究，大多源自实验室机制性实验，未必针对社会性物种。因此，目前仍不清楚这些已报道的雌性替代形态间的差异，在野生自然种群中能够在多大程度上真实存在。我们在高度社会性的啮齿类动物八齿鼠（Octodon degus）的自然种群中，量化了雌性替代形态对雌性繁殖性状的影响。我们通过肛殖距（anogenital distance）的连续梯度来评估雌性替代形态：雌性化个体的肛殖距接近该梯度的短端，而雄性化个体则接近该梯度的长端。我们同时检验了“社会环境与雌性形态类型交互作用可影响雌性繁殖性状”这一假说。在八齿鼠雌性个体中，仅母体体重会对窝仔数产生影响——体重更重的雌性断奶的后代数量更多。雄性化雌性产下的幼崽以雄性为主，且断奶的后代体重更大。此外，相较于雌性化雌性，雄性化雌性的分娩时间在繁殖季中更晚。与此前的研究论断相反，我们的研究结果并不支持“雄性化雌性的繁殖能力低于雌性化雌性”这一观点。此外，相较于雌性化个体，雄性化雌性产下的后代体重更大，潜在品质也更高。