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

宿主-寄生虫共同进化是进化的适应性驱动力之一。现在人们普遍认为，寄主和寄主寄生的寄生虫正在进行一场永无止境的军备竞赛，每一代都应该重新选择最适合的寄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的局部适应而告终。虽然对理解适应性进化至关重要，但遗传解决的局部适应的例子很少。主要组织相容性复合体（MHC）在寄生虫抗性中起着关键作用，是研究寄生虫介导的宿主局部适应的理想候选者。在本项目中，我们利用三棘棘鱼在复制但遗传上不同的湖泊/河流生态型中的发生，研究MHC基因的潜在局部适应性及其对寄生虫遗传库的影响。来自这些栖息地类型的鱼类携带不同种类的寄生虫，其中Gyrodactylus gasterostei是一种常见的棘鱼吸虫，在不同的栖息地类型中，它的遗传差异和感染强度一致。以第二代实验室培育的湖泊和河流三棘鱼为研究对象，采用野外和室内实验相结合的方法，研究宿主MHC基因型对栖息地特异性寄生虫的适应性。2)宿主MHC基因型对寄生虫达尔文适应度的影响。由于鱼类的定量育种设计，在这两种情况下，选择的相互强度将被量化，而不依赖于鱼类的遗传背景。这项工作将是遗传解决宿主局部适应的唯一例子，并将证明宿主分布在影响寄生虫种群遗传结构方面的作用。最后，但并非最不重要的是，这种育种方案是测试Reusch， Bornberg-Bauer和Stoll在野外发现的免疫相关基因的理想系统。

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.