Host-parasite interactions in hybridizing Daphnia, from correlations to experiments

富营养化是一个世界性的环境问题，由于全球变暖而加速，影响到水生生态系统的稳定，并产生长期的后果。我们建议调查是否以及如何富营养化影响两个相互作用的进化过程：疾病传播和种间杂交。我们将研究富营养化对杂交系统中宿主-寄生虫相互作用和杂交成功本身的影响。我们将使用水蚤（水蚤）作为杂交宿主和鱼孢子虫Caullerya作为病原体。该牵头机构项目结合了两个湖泊（德国Müggelsee和瑞士Greifensee）的实地调查、大规模池塘实验（CH）、压力暴露水蚤（CH）的转录谱分析以及分子标记（DE）的开发和应用，使我们能够研究杂交水蚤中的寄生虫进化。18个实验池塘将接种100个水蚤克隆，然后将经历高，中或低营养条件和存在或不存在寄生虫。这些克隆是从Greifensee的水柱中分离出来的，或者是从保存在湖泊沉积物中的滞育卵中孵化出来的，代表了不同的起源年龄，不同的物种和杂交种。我们将测试是否水蚤，用来生活在Greifensee高度富营养化的条件下（20世纪60年代至70年代）更好地适应高营养负荷比克隆，经历了清洁的条件later on. Then，我们预计，流行病将更大的富营养化池塘，因为蓝藻的存在，这似乎有利于Caullerya感染。我们的目标是开发一套多态性的分子标记的寄生虫Caullerya，能够测试寄生虫感染宿主基因型的菌株特异性的方式，如果这些协会进一步塑造的营养条件。这些标记物将用于池塘和实地研究。为了获得一个机械的理解，以前观察到的寄生虫流行和蓝藻水华（富营养化的副产品）之间的相关模式，水蚤将转录下的寄生虫和无寄生虫的条件下，而在存在或不存在蓝藻。最后，使用水蚤的长期现场收集，我们将验证如果病原体的传播加剧蓝藻的存在下。这项拟议中的研究是瑞士和德国科学团队密切合作的结果，将促进我们对推动自然系统进化过程的环境力量的理解。总的来说，通过独特的专业知识和方法的结合，该项目将提高我们对不同营养条件下疾病传播和生物多样性丧失的理解，从而可能为水生生态系统的管理提供工具。

Eutrophication is a worldwide environmental problem accelerated by global warming, affecting the stability of aquatic ecosystems and having long-lasting consequences. We propose to investigate if and how eutrophication affects two interacting evolutionary processes: disease spread and interspecific hybridization. We will study the influence of eutrophication on host-parasite interactions in a hybridizing system and on hybridization success per se. We will use waterfleas (Daphnia) as a hybridizing host and the ichthyosporean Caullerya as a pathogen. This Lead Agency Project is a combination of field surveys of two lakes (Müggelsee, DE and Greifensee, CH), a large scale pond experiment (CH), the transcriptional profiling of stress-exposed Daphnia (CH), and the development and application of molecular markers (DE) that will allow us to study parasite evolution in hybridizing Daphnia. Eighteen experimental ponds will be inoculated with 100 Daphnia clones, which will then experience high, moderate or low trophic conditions and presence or absence of parasites. These clones were isolated from the water column of Greifensee or hatched from diapausing eggs preserved in the lake sediment, representing different ages of origin, and different species and hybrids. We will test whether Daphnia that used to live in Greifensee under highly eutrophic conditions (1960s-70s) are better adapted to high nutrient load than clones that experienced cleaner conditions later on. Then, we expect that epidemics will be greater in eutrophic ponds, because of the presence of cyanobacteria which seem to facilitate Caullerya infection. We aim to develop a set of polymorphic molecular markers for the parasite Caullerya, to be able to test if the parasite infects host genotypes in a strain-specific manner and if these associations are further shaped by trophic conditions. These markers will be used in the pond and in the field studies. To gain a mechanistic understanding of the previously observed correlational pattern between parasite epidemics and blooms of cyanobacteria (a by-product of eutrophication), Daphnia will be transcriptionally profiled under parasite and parasite-free conditions while in the presence or absence of cyanobacteria. Finally, using long-term field collections of Daphnia, we will verify if pathogen spread is intensified under the presence of cyanobacteria. The proposed research, a result of close collaboration between Swiss and German scientific teams, will advance our understanding of the environmental forces driving evolutionary processes in natural systems. Overall, through the unique combination of expertise and methods, this project will improve our understanding of disease spread and biodiversity loss under different trophic conditions and, consequently, might provide tools for management of aquatic ecosystems.