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

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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.