Dissecting the Mechanisms of Host-Parasite Coevolution Mediating Reciprocal Local Adaptation CLUSTER: "Evolutionary Genetics of Three-Spined Stickleback - Parasite Interactions"

寄主-寄生虫协同进化是适应性进化的驱动力之一。现在人们普遍认为，宿主和寄生虫正在进行一场永无止境的军备竞赛，每一代都应该选择最适合的宿主和最适合的寄生虫的基因型。这种军备竞赛往往以一方或双方在当地进行适应性调整而告终。虽然对于理解适应性进化至关重要，但遗传上解决局部适应的例子很少。主要组织相容性复合体（MHC）是研究寄生虫介导的宿主局部适应性的理想分子。在这个项目中，我们利用发生在复制，但遗传上不同的湖泊/河流生态类型的三刺棘鱼调查潜在的本地适应的MHC基因及其对寄生虫遗传库的影响。来自这些栖息地类型的鱼具有不同的寄生虫物种，其中Gyrodactylus gasterostei -一种常见的棘背吸虫寄生虫，其在遗传上不同，并且在栖息地类型之间的感染强度一致。本研究采用野外和室内实验相结合的方法，以实验室培育的第二代三棘鱼为材料，研究了1）宿主MHC基因型对生境特异性寄生虫的适应性。2)寄生虫的达尔文适应性受宿主MHC基因型的影响。由于鱼类定量育种设计，在这两种情况下，选择的相互强度将独立于鱼类遗传背景进行量化。这项工作将是唯一的例子，遗传解决主机的地方适应，并将展示主机分布在影响寄生虫种群遗传结构的作用。最后，但并非最不重要的是，这样的育种方案代表了理想的系统来测试由Reusch，Bornberg-Bauer和Stoll在该领域鉴定的免疫相关基因。

Host-parasite coevolution is known to be one of the adaptive driving forces of evolution. It is now accepted that hosts and their parasites are engaged in a never ending arms race which should select for the fittest hosts’ and the fittest parasites’ genotypes every generation anew. This arms race often ends in local adaptation of either one or both partners. Though crucial for the understanding of adaptive evolution, genetically resolved examples of local adaptation are rare. The major histocompatibility complex (MHC) with its key function in parasite resistance represents an ideal candidate to investigate parasite-mediated host local adaptation. In this project, we take advantage of the occurrence of the three-spined sticklebacks in replicated but genetically distinct lake/river ecotypes to investigate the potential local adaptation of MHC genes and its influence on the parasite genetic pools. Fish from those habitat types harbor different parasite species among which Gyrodactylus gasterostei - a common stickleback trematode parasite which varies genetically and consistently in intensity of infection between habitat types. Using a combination of field and lab experiments based on second generation of lab-bred three-spined stickleback hybrids of lake and river population, we aim to test for 1) host local adaptation of MHC genotypes to habitat-specific parasites. 2) parasite’s Darwinian fitness influenced by the host MHC genotypes. Thanks to the fish quantitative breeding design, in both cases, the reciprocal strength of selections will be quantified independently of the fish genetic background. Such work would represent the only example of genetically resolved host local adaptation and would demonstrate the role of host distribution in affecting parasite population genetic structure. And last, but not least, such a breeding scheme represents ideal system to test for immune related genes identified by Reusch, Bornberg-Bauer and Stoll in the field.