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

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, behavioural 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.

相较于雄性个体，雌性的替代形态型（alternative morphotypes）的报道频率更低。这一规律的一个例外，是部分雌性哺乳动物中报道的表型雄性化（phenotypical masculinization）梯度：其中雌性化与雄性化雌性个体分别处于该梯度的两端。这类表型差异起源于产前发育阶段，由母体效应（maternal effects）介导。雌性化与雄性化雌性个体在多项性状上存在差异，涵盖形态学、生理学、行为学与繁殖学性状。
此前关于雌性化与雄性化雌性个体间繁殖性状差异的报道，大多源于实验室机制性研究，未必针对社会性物种。因此，目前尚不清楚雌性替代形态型间的这些报道差异，在野生自然种群中的实际体现程度。
本研究以高度社会性啮齿类动物八齿鼠（Octodon degus）的自然种群为研究对象，量化了雌性替代形态型对雌性繁殖性状的影响。研究通过肛殖距（anogenital distance）的连续梯度对雌性替代形态型进行评估：雌性化个体的肛殖距处于较短区间，而雄性化个体则处于该梯度的较长区间。本研究同时验证了“社会环境与雌性形态型交互作用影响雌性繁殖性状”这一假说。
在八齿鼠雌性个体中，仅体重会影响窝仔数——体重更重的雌性，其断奶的后代数量更多。雄性化雌性所产的窝仔偏向雄性，且断奶的后代体重更大。最后，相较于雌性化个体，雄性化雌性的繁殖季产仔时间更晚。
与此前的研究结论相悖，本研究结果并不支持“雄性化雌性生育能力弱于雌性化雌性”这一观点。此外，相较于雌性化个体，雄性化雌性所产后代的体重更大，潜在质量也更高。