Interactive effects of environmental change and host-parasite co-evolution on the ecological speciation of sticklebacks

人类造成的环境变化如何影响创造和维持生物多样性的生态和进化过程，是生物学中一个紧迫的问题。水生生态系统的富营养化是一个广泛和持续存在的问题，对维持关键的生态系统服务，包括水质和生物多样性，具有多种后果。淡水环境中营养物质(如磷和氮)的负荷不仅影响它们的化学和物理条件，而且还影响物种之间相互作用的性质，例如宿主与寄生虫的相互作用，这会产生局部适应模式，甚至可能导致物种形成。富营养化的普遍影响可以改变选择机制，因此，在短时间尺度上导致种群的意外进化变化。在这里，我们使用三刺刺鱼作为模型系统，重点研究营养负荷和寄生虫的交互作用如何推动局部适应的快速进化变化和崩溃。首先，利用沿着湖泊生产力梯度的密集实地调查，我们将测试湖泊生产力如何随着i)寄生虫多样性和群落组成，ii)宿主基因多样性，以及iii)宿主免疫系统功能和基因表达测试-宿主和寄生虫种群的局部适应-而发生变化。其次，利用中胚层(42×1000 L)的大规模实验，我们将测试由寄生虫和营养水平的正交组合产生的不同的自然选择制度如何影响刺鱼的表型和基因适应能力。在本实验中，我们将重点放在与配偶选择有关的表型和遗传性状上，以便我们能够测试由于(拮抗)操纵营养物质和寄生虫而导致的相反的选择制度是否可能有助于种群分化，并在(反向)物种形成中发挥作用。这项工作将阐明自然选择和性选择如何受到寄生虫和环境条件的调节，以及这些过程如何共同应对不同的环境并影响物种形成的进程。

How human-caused environmental change affects the ecological and evolutionary processes that create and maintain biodiversity is a pressing question in biology. The eutrophication of aquatic ecosystems is a widespread and ongoing problem that has manifold consequences for sustaining critical ecosystem services, including water quality and biodiversity. The loading of nutrients (e.g. phosphorus and nitrogen) to freshwater environments not only affects their chemical and physical condition, but also influences the nature of interactions between species such as host-parasite interactions which generate local adaptation patterns and may even lead to speciation. Pervasive effects of eutrophication can alter selection regimes and therefore, cause unexpected evolutionary changes in populations over short time scales. Here, using three-spined stickleback as a model system, we focus on how the interactive effects of nutrient loading and parasites might drive rapid evolutionary changes and breakdown of local adaptation. First, using an intensive field survey along a lake productivity gradient, we will test how lake productivity co-varies with i) parasite diversity and community composition, ii) host genotype diversity, and iii) host immune system function and gene expression- testing for local adaptation of host and parasite populations. Second, using a large scale experiment in mesocosms (42 X 1000 L), we will test how contrasting natural selection regimes, resulting from orthogonal combinations of parasites and nutrient levels, can affect phenotypically and genotypically stickleback adaptive abilities. In this experiment, we focus on phenotypic and genetic traits that have been implicated in mate selection, so that we can test if the contrasting selection regimes caused by manipulating nutrients and parasites (antagonistically) synergistically might contribute to population divergence, and play a role in (reverse) speciation. This work will shed light on how natural and sexual selection are mediated by parasites and environmental conditions, and how these processes jointly respond to divergent environments and affect the progress towards speciation.