Sex differences in immunity have been described in humans and other mammal species. Females have a lower incidence of infections and non-reproductive malignancies and exhibit higher antibody levels after vaccination. Existing evolutionary explanations are based on differences in reproductive strategies and reaction to extrinsic differences in susceptibility and virulence between the sexes. Here, we test the hypothesis that known differences in the probability of transmission and outcome of sexually transmitted infections contribute to sex differences in immunocompetence. We modelled reproductive and immune investments against a fertility limiting Sexually Transmitted Infection (STI). We show that, in line with previous findings, increased susceptibility selects for tolerance to the parasite while increased virulence selects for resistance against it. Differences in reproductive strategies between the sexes lead to sex differences in immunocompetence, mostly with higher competence in females. Extrinsic differences in susceptibility and virulence between the sexes can augment or alleviate the evolutionary consequences of intrinsic differences depending on their direction and magnitude. This indicates that the selection of sex-specific immune strategies is less predictable than thought before and explains why sex differences in immunity have been found to be not universal and pervasive across animal species.

中文翻译：

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性传播感染选择两种性别的免疫能力和生殖力的不同水平

在人类和其他哺乳动物中已经描述了免疫力的性别差异。女性的感染和非生殖性恶性肿瘤发病率较低，接种疫苗后抗体水平较高。现有的进化论解释是基于生殖策略的差异以及对性别之间对外在差异的敏感性和毒力的反应。在这里，我们检验了以下假设：已知的传播可能性和性传播感染的结果差异会导致免疫能力方面的性别差异。我们模拟了针对生育能力限制性传播感染（STI）的生殖和免疫投资。我们证明，根据先前的发现，增加的药敏性选择对寄生虫的耐受性，而增加的毒力则选择对寄生虫的抗性。性别之间在生殖策略上的差异导致免疫能力方面的性别差异，其中大多数是女性。性别之间在敏感性和毒力方面的外在差异可以增加或减轻内在差异的进化后果，这取决于性别和方向。这表明性别特异性免疫策略的选择比以前想像的要难预测，并解释了为什么发现免疫中的性别差异在动物物种中并不普遍且普遍存在的原因。性别之间在敏感性和毒力方面的外在差异可以增加或减轻内在差异的进化后果，这取决于性别和方向。这表明性别特异性免疫策略的选择比以前想像的要难预测，并解释了为什么发现免疫中的性别差异在动物物种中并不普遍且普遍存在的原因。性别之间在敏感性和毒力方面的外在差异可以增加或减轻内在差异的进化后果，这取决于性别和方向。这表明性别特异性免疫策略的选择比以前想像的要难预测，并解释了为什么发现免疫中的性别差异在动物物种中并不普遍且普遍存在的原因。