MHC gény triedy IIB u kaprovitých rýb: vzťahy medzi MHC variabilitou a diverzitou parazitov
| Title in English | MHC IIB genes in cyprinid fish: the associations between MHC variability and parasite diversity |
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| Authors | |
| Year of publication | 2006 |
| Type | Article in Proceedings |
| Conference | IX. Česká ichtyologická konference, Vodňany 2006, Sborník abstraktů z konference |
| MU Faculty or unit | |
| Citation | |
| Field | Zoology |
| Keywords | MHC IIB genes-cyprinid fish-parasite mediated selection |
| Description | The highly polymorphic MHC (major histocompatibility complex) genes play a central role in controlling immunological self and non-self recognition, and they permit to recognize the foreign antigens. The MHC variability is maintained by balancing selection potentially caused by pathogens and parasites, and a link between diversity of the MHC genes and pathogens or parasites have been hypothesised. In this study, we presented three different levels of analyses investigating a potential link between MHC variability and parasite diversity: (1) a comparative study using a large number of cyprinid fish; (2) a population study of chub (Leuciscus cephalus); (3) within population analysis using males of common bream (Abramis brama). (1) Considering the fact that host immune system evolves through life history trade-offs, one could hypothesize that the variability of genes related to host immune defence may be associated with life history traits and parasitism. MHC genes represent a suitable candidate to test this hypothesis. We supposed that metazoan parasite diversity could be a selective force driving the MHC polymorphism in cyprinid fish. The prediction, that fish species exposed to the high parasite pressure (especially represented by specific ectoparasite species) maintain the more diverse MHC, was tested. Moreover, we analysed potential associations between the MHC variability and fish life-history traits, using independent contrasts method. Our results suggest that fish species exposed to high parasite species richness, maintain a high genetic variability of the exon 2 of the MHC genes (presenting the peptide binding regions), allowing them to decrease their natural mortality rate. (2) The potential role of the metazoan parasites on the differentiation of MHC genes was investigated in six populations of the chub collected from the different water basins not historically connected. We found that more similar fish populations in parasite communities (i.e. using the presence data) tended to be more similar in their MHC variability calculated for exon 2. Geographically separated populations were more different using microsatellites markers but the more similar when analyzing non-synonymous substitutions of MHC genes. (3) The potential associations between the following host traits: immunocompetence, expression of resistance genes, sexual ornamentation, condition status and parasitism were predicted and tested in fish males following the hypotheses of (1) sexual selection, (2) immunocompetence handicap, and (3) trade-offs in energy allocation. We found that MHC diversity is associated with metazoan parasites (predominantly ectoparasites) in males of common bream. The type of expressed alleles (i.e. allelic groups) was important for fish condition status and level of parasitism, i.e. the expression of different allelic groups seems to be advantageous for fish males. Moreover, MHC diversity reflects a status of host vigour measured by condition factor. A support for the connection between sexual ornamentation and MHC diversity was also provided when fish with a single type of alleles expressed more intensively their ornamentation (i.e. the number and size of breeding tubercles). |
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