Mammal sex allocation research has focused almost exclusively on maternal traits, but it is now apparent that fathers can also influence offspring sex ratios. Parents that produce female offspring under conditions of intense male-male competition can benefit with greater assurance of maximized grand-parentage. Adaptive adjustment in the sperm sex ratio, for example with an increase in the production of X-chromosome bearing sperm (CBS), is one potential paternal mechanism for achieving female-biased sex ratios. Here, we tested this mechanistic hypothesis by varying the risk of male-male competition that male house mice perceived during development, and quantifying sperm sex ratios at sexual maturity. Our analyses revealed that males exposed to a competitive 'risk' produced lower proportions of Y-CBS compared to males that matured under 'no risk' of competition. We also explored whether testosterone production was linked to sperm sex ratio variation, but found no evidence to support this. We discuss our findings in relation to the adaptive value of sperm sex ratio adjustments and the role of steroid hormones in socially induced sex allocation.

中文翻译：

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哺乳动物精子性别比的调整：男性竞争会导致女性产生精子的比例增加。

哺乳动物性别分配研究几乎完全集中在母性特征上，但是现在很明显，父亲也可以影响后代性别比例。在激烈的男女竞争条件下生产雌性后代的父母可以受益于更大的祖父母最大化的保证。精子性别比的适应性调节，例如随着X染色体承载精子（CBS）产量的增加，是实现女性偏向性别比的一种潜在的父源机制。在这里，我们通过改变雄性家鼠在发育过程中感知到的雄性-雄性竞争的风险，并量化性成熟时精子的性别比，来测试这种机制的假设。我们的分析表明，与具有竞争性“风险”的男性相比，在“ 没有竞争的风险。我们还探讨了睾丸激素的产生是否与精子性别比的变化有关，但没有证据支持这一点。我们讨论了有关精子性别比例调整的适应性价值和类固醇激素在社会性别分配中的作用的发现。