Publication details
Genetic variability of MHC class IIB genes associated with parasite diversity in European populations of chub (Leuciscus cephalus Linnaeus, 1758)
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| Year of publication | 2007 |
| Type | Appeared in Conference without Proceedings |
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| Description | The genes of the major histocompatibility complex (MHC) are the most polymorphic loci known for vertebrates. The host- pathogen coevolution and parasite-driven balancing selection have a extensive contribution to the high level of allelic diversity in MHC genes. The polymorphism of MHC molecules can be extremely huge; there are a large number of genetic variants (alleles) at each genetic locus. Individuals with higher number of different MHC molecules are able to recognize a broader spectrum of pathogen or parasite derived antigens, and then pathogens or parasites evolve to evade common MHC genotypes, giving rare MHC genotypes a selective advantage. A common European cyprinid, the chub, Leuciscus cephalus (L.), was chosen as a model organism for investigating the hypothesis of pathogen-driven selection under natural conditions, mediated either through heterozygous advantage (overdominant selection) or negative frequency-dependent selection (rare allele advantage hypothesis). There is a prediction that the populations with more genetic variability of MHC will have more diverse array of parasites. Therefore, the aims of this project were: (1) to study the diversity of metazoan parasites and compare the parasite communities of chub in relation to geographic distances between fish populations; (2) to investigate the variability of the exon 2 of MHC class IIB gene corresponding to ß1 domain of this class which includes the most polymorphic part of class II genes, the peptide binding regions (PBR); (3) to analyze fish populations using microsatellite loci, as a neutral marker; (4) to investigate the relationships between MHC, microsatellite variability and parasitism and finally (5) to examine whether the geographic distances and historical associations among localities have influenced the degree of genetic variation. The fish were caught using electrofishing in the selected different localities in Europe including a high range of chub distribution. Basic epidemiological parameters and parasite component community indexes were computed for each fish population. The variability of the exon 2 of DAB genes (MHC class IIB) was analyzed using SSCP, cloning and sequencing. All identified parasite species represent 8 higher metazoan parasite taxa: Monogenea, Crustacea (parasitic Copepoda), Mollusca, Hirudinea, Digenea, Acantocephala, Nematoda and Cestoda. Chub harbored more ectoparasites than endoparasites species. The highest values of abundance, prevalence and mean intensity of infection were observed for monogenean species. The geographical distances among fish populations were associated with microsatellite variability. The results indicated the relationship between MHC allelic diversity and parasite occurrence, i.e. the more parasitized populations of chub (level of parasite infection estimated by Shannon index diversity or Simpson index of dominance) reached the high level of MHC variability. This study was funded by the Grant Agency of the Czech Republic, Project No. 524/04/1128 and Research Project of the Masaryk University, Brno MSM 0021622416. |
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