PDF(Sci-hub)
Abstract：
Neighboring fetuses may impact their siblings in various respects, depending on their in utero location and sex. The effects of the intrauterine position (IUP) are widely studied in model organisms, especially laboratory bred murine strains that are characterized by short gestations and altricial offspring. In some species, the proximity to a male fetus and its higher circulating testosterone masculinizes neighboring female fetuses. In utero testosterone exposure might be manifested as higher testosterone concentrations, which contribute to a variation in morphology, reproductive potential and behavior. In this study, we examined the influence of neighboring an opposite sex fetus on testosterone levels in a feral animal model characterized by a long gestation and precocious offspring. Using necropsies of culled nutria (Myocastor coypus), we accurately determined the IUP and quantified testosterone immunoreactivity in fetal hair. We found that as expected, both male and female fetuses neighboring a male in utero had longer anogenital distance. However, females adjacent to males in utero showed lower testosterone levels than male fetuses, while testosterone levels of females without a male neighbor did not differ from those of males. This surprising result suggests an alternative mode by which local exogenous steroids may modify the local fetal environment. Our study emphasizes the importance of examining known phenomena in species with different life histories, other than the traditional murine models, to enhance our understanding of the evolutionary mechanisms that are driving sexual differentiation.
摘要：
邻近的胎儿可能会在各个方面影响他们的兄弟姐妹，取决于他们在子宫内的位置和性别。宫内位置（IUP）的影响在模型生物中被广泛研究，特别是实验室培育的鼠类品系，其特征是妊娠时间短，后代长。在某些物种中,接近男性胎儿和其较高的循环睾酮使邻近的女性胎儿男性化。子宫内睾酮暴露可能表现为更高的睾酮浓度，这有助于形态的变化，生殖潜力和行为。在这项研究中,我们研究了以长期妊娠和早熟后代为特征的野性动物模型中，异性胎儿对睾丸激素水平的影响。使用剔除的营养品(Myocastorcoypus)的尸检，我们准确测定了胎儿毛发中的IUP和定量的睾酮免疫反应性.我们发现正如预期的那样，子宫内与男性相邻的男性和女性胎儿的肛门生殖器距离都更长。然而,子宫内与男性相邻的女性睾丸激素水平低于男性胎儿，而没有男性邻居的女性的睾丸激素水平与男性的睾丸激素水平没有差异。这一令人惊讶的结果表明了一种替代模式，通过这种模式，局部外源性类固醇可以改变局部胎儿环境。我们的研究强调了检查具有不同生活史的物种中已知现象的重要性，除了传统的鼠类模型，加强我们对推动性分化的进化机制的理解。
