The epidemiology of sexually transmitted infections (STIs) is inherently linked to host mating dynamics. Studies across many taxa show that adult sex ratio, a major determinant of host mating dynamics, is often skewed - sometimes strongly - toward males or females. However, few predictions exist for the effects of skewed sex ratio on STI epidemiology, and none when coupled with sex biased disease characteristics. Here we use mathematical modelling to examine how interactions between sex ratio and disease characteristics affect STI prevalence in males and females. Notably, we find that while overall disease prevalence peaks at equal sex ratios, prevalence per sex peaks at skewed sex ratios. Furthermore, disease characteristics, sex-biased or not, drive predictable differences in male and female STI prevalence as sex ratio varies, with higher transmission and lower virulence generally increasing differences between the sexes for a given sex ratio. These findings may be due to a balance between increased per-capita mating in the less common sex, and a reduction in mating rate - hence disease prevalence - at the population level. Our work reveals new insights into how STI prevalence in males and females depends on a complex interaction between host population sex ratio and disease characteristics.

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性别比例和疾病特征的偏向如何影响性传播感染的传播？

性传播感染（STIs）的流行病学固有地与宿主交配动态相关。对许多分类单元的研究表明，成年性别比是决定宿主交配动态的主要因素，通常偏向于男性或女性，有时甚至是男性。然而，几乎没有关于性别比例偏倚对性传播疾病流行病学影响的预测，而与性别偏见的疾病特征相结合则没有任何预测。在这里，我们使用数学模型来检验性别比和疾病特征之间的相互作用如何影响男性和女性的性传播感染患病率。值得注意的是，我们发现，虽然总体疾病患病率在相同的性别比时达到峰值，但每性别的患病率在偏斜的性别比时达到峰值。此外，随着性别比例的变化，不论性别歧视与否，疾病特征都会导致男性和女性性传播感染的发生率发生可预测的差异，对于给定的性别比例，更高的传播率和更低的毒力通常会增加性别之间的差异。这些发现可能是由于在较不常见的性别中人均增加的交配与人口水平上的交配率（因此疾病患病率）降低之间取得了平衡。我们的工作揭示了关于男性和女性中性传播感染患病率如何取决于寄主人口性别比与疾病特征之间复杂相互作用的新见解。