000K utf8 1100 $c2004 1500 eng 2050 urn:nbn:de:gbv:8-diss-12060 3000 Wegner, K. Mathias 4000 Major histocompatibility genes, polymorphism and balancing selection : the case of parasites and sticklebacks$hChristian-Albrechts-Universität zu Kiel [Wegner, K. Mathias] 4030 Kiel$nChristian-Albrechts-Universität zu Kiel 4209 The extreme polymorphism of genes of the vertebrate major histocompatibility complex is an evolutionary puzzle. Why do high numbers of alleles persist despite selective forces favouring the fittest variants? Overdominant selection can explain the persistance of high numbers of alleles, because MHC heterozygotes can detect more pathogens. Using three-spined sticklebacks and their natural parasite fauna as a model organisms, this thesis addresses some of the key mechanisms that may explain MHC polymorphism. On Population level, diversity of stickleback MHC class IIB genes was correlated with parasite diversity. Within individuals those with an intermediate individual MHC diversity were suffering least from parasite infection in the field and in controlled experiments. Host-parasite co-evolution would further predict that the fitness of genotypes/alleles should fluctuate depending on its frequency. In three populations MHC alleles fluctuate stronger between generations than random. These fluctuations could partly be linked to changes in parasite prevalence and therefore provide support for antagonistic co-evolution between MHC genes and parasites. 4950 https://nbn-resolving.org/urn:nbn:de:gbv:8-diss-12060$xR$3Volltext$534 4961 https://macau.uni-kiel.de/receive/diss_mods_00001206 5051 570 5550 co-evolution 5550 Dreistachliger Stichling 5550 frequency dependent selection 5550 Gasterosteus aculeatus 5550 major histocompatilibility complex 5550 MHC 5550 overdominant selection 5550 Parasit 5550 parasites 5550 three-spined stickleback