Data from: Highly masculinized and younger males attain higher reproductive success in a social rodent

Abstract: Alternative morphotypes have been reported in males of different taxa. In some mammals highly masculinized and slightly masculinized males represent two opposite ends along a gradient of phenotypic variation in males. This phenotypical gradient originates during prenatal development. Laboratory studies have documented how highly and slightly masculinized males differ in several traits, including their reproductive success. However, the extent to which these reported differences materialize in natural populations remains unknown. We quantified the impact of male morphotype on male reproductive success in a natural population of Octodon degus, a highly social rodent. We assessed male morphotype through a continuous gradient of anogenital distance. We also tested the hypothesis that the social environment interacts with male morphotype to influence male reproductive success. We found that individual attributes, including masculinization level and age, impacted male reproductive success. Highly masculinized and younger males had greater reproductive success. Additionally, male body weight had a small magnitude but positive effect on male reproductive success. Male reproductive success was not affected by social attributes such as group composition. Thus, the number of males and females within a group did not affect male reproductive success, nor did the average male anogenital distance within a group. Our results support the hypothesis that the prenatal environment can result in long-term effects on individual life history and cause intrasexual phenotypical variation in natural populations. Our findings suggest that male phenotypical masculinization could be an adaptive trait, regardless of the social environment.

摘要：不同分类群（taxa）的雄性个体中均已被报道存在替代性形态型（alternative morphotypes）。在部分哺乳动物类群中，高度雄性化与轻度雄性化的雄性个体，代表了雄性表型变异梯度上的两个极端。该表型梯度起源于产前发育阶段。实验室研究已证实，高度与轻度雄性化的雄性在多项性状上存在差异，其中包括繁殖成功率。然而，这些已报道的性状差异在自然种群中实际体现的程度仍不明确。我们以高度社会化的啮齿类动物八齿鼠（Octodon degus）的自然种群为研究对象，量化了雄性形态型对雄性繁殖成功率的影响。我们通过肛殖距（anogenital distance）的连续梯度值来评估雄性形态型。此外，我们检验了“社会环境与雄性形态型相互作用，进而影响雄性繁殖成功率”这一研究假说。研究结果显示，包括雄性化程度与年龄在内的个体属性，会对雄性繁殖成功率产生影响：高度雄性化且年龄较小的雄性个体拥有更高的繁殖成功率。此外，雄性体重对繁殖成功率具有微弱但正向的影响效应。雄性繁殖成功率不受群体组成等社会属性的影响，即群体内雄性与雌性的数量，以及群体内雄性平均肛殖距均未对雄性繁殖成功率产生显著作用。我们的研究结果支持“产前环境可对个体生活史（life history）产生长期影响，并导致自然种群内出现种内表型变异”这一假说。本研究结果提示，雄性表型的雄性化程度或许是一种适应性性状，且其效应不受社会环境的影响。