Causes of sex ratio bias in Malagasy plovers: experimental tests of the role of parasites and immuno-competence

成年人的性别比例（ASR，成年人口中男性的比例）是人口统计学的核心概念，也是性选择下进化的关键因素。作为最近DFG资助的研究项目（KR 2089/9-1）的一部分，我们开发了一个人口统计模型来估计一种经过充分研究的滨鸟，雪普洛弗Charadrius nivosus的ASR（Eberhart-Phillips et al. 2017 in PNAS）。重要的是，我们还使用这种阶段特异性矩阵模型来估计六个密切相关的普洛弗种群的ASR（Eberhart-Phillips et al. 2018 in Nature Communications）。这是迄今为止使用基于异常大样本量个体（总计3862只小鸡和3107只成年鸡）的人口模型进行的最全面的ASR比较研究。后一项工作揭示了物种和种群之间在ASR中存在很大的差异，从强烈的男性偏见到强烈的女性偏见。我们还表明，生存的性别偏见通常在生命的第一年最强烈。因此，影响早期生命阶段的未知因素似乎是多个物种ASR变化的主要驱动因素。更重要的是，在普洛弗种群中ASR的变化与父母的合作程度有关。在这里，我们试图测试鸡和成人的性别特异性死亡率的原因，重点是细菌和寄生虫感染和由此产生的免疫反应。我们将比较模式的性别特异性免疫和寄生虫压力之间的三个同域种群密切相关的普洛弗种不同的交配系统在马达加斯加。免疫防御成分和死亡率的性别差异可能是由于睾酮免疫抑制，可以预期大多在性腺成熟的成年人，而其他因素可能会导致青少年死亡率的性别差异。因此，我们将同时研究青少年和成年人。然后，我们的目标是将我们的实验结果到完善的人口模型的ASR和交配系统的变化，使用基于个人的模型和综合人口模型。这些模型将探讨不同性别的生存率对不同人群中ASR演变的影响以及相关的人群增长轨迹。

The adult sex ratio (ASR, proportion of males in the adult population) is a central concept in population demography and a key factor in evolution under sexual selection. As part of a recent DFG-funded research project (KR 2089/9-1), we developed a population demographic model to estimate ASR in a well-studied shorebird, the snowy plover Charadrius nivosus (Eberhart-Phillips et al. 2017 in PNAS). Importantly, we also used this stage-specific matrix model to estimate ASR in six closely related plover populations (Eberhart-Phillips et al. 2018 in Nature Communications). This is currently the most comprehensive comparative study of ASR to date using demographic models based on unusually large sample sizes of individuals (totalling 3862 chicks and 3107 adults). The latter work has revealed large variation among species and populations in ASR, ranging from strongly male-biased to strongly female-biased. We have also shown that sex-biases in survival are generally strongest during the first year of life. Consequently, as yet unknown factors that influence early life-stages appear to be the main drivers of ASR variation across multiple species. Importantly, ASR variation among plover populations is associated with the extent of parental cooperation. Here, we seek to test the causes of sex-specific mortalities in chicks and adults by focusing on bacterial and parasite infection and the resulting immune response. We will compare patterns of sex-specific immunity and parasite pressures among three sympatric populations of closely-related plover species with different mating systems in Madagascar. Sex differences in immune defence components and mortality could be due to testosterone immunosuppression and can be expected mostly during gonadal maturation in adults, while other factors may cause sex differences in juvenile mortality. Therefore, we will study both juveniles and adults in parallel. We then aim to incorporate our experimental findings into refined demographic models of ASR and mating system variation, using both individual-based models and integrative population models. These models will explore the consequences of sex-specific survival for the evolution of ASR across populations and associated population growth trajectories.