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

成人性别比(ASR，成年人口中男性的比例)是人口统计学中的一个核心概念，也是性别选择下进化的关键因素。作为DFG最近资助的一个研究项目(KR 2089/9-1)的一部分，我们开发了一个种群人口模型来估计一种研究得很好的滨鸟--雪鸟Charadrius nivosus(Eberhart-Phillips等人)的ASR。2017年在PNAS中)。重要的是，我们还使用了这个特定阶段的矩阵模型来估计六个密切相关的越冬种群的ASR(Eberhart-Phillips等人。2018年在《自然通讯》上)。这是目前为止对ASR进行的最全面的比较研究，使用基于异常大的个体样本量的人口统计模型(总计3862只雏鸟和3107只成鸟)。后一项工作揭示了ASR物种和种群之间的巨大差异，从强烈的男性偏见到强烈的雌性偏见不等。我们还表明，在生命的第一年，生存中的性别偏见通常最强烈。因此，到目前为止，影响早期生命阶段的未知因素似乎是ASR在多个物种中变异的主要驱动因素。重要的是，群体间的ASR差异与亲本合作的程度有关。在这里，我们试图通过关注细菌和寄生虫感染以及由此产生的免疫反应来测试雏鸟和成虫性别特异性死亡的原因。我们将比较马达加斯加三个具有不同交配系统的密切相关物种的共域种群的性别特异性免疫和寄生虫压力。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，主要是在成人性腺成熟期间，而其他因素可能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结合到ASR和交配系统变异的精细化人口统计模型中，使用基于个体的模型和综合种群模型。这些模型将探索特定性别的生存对ASR在人群中的进化以及相关的人口增长轨迹的影响。

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.