Characterization of MHC class II genes in the critically endangered European eel (Anguilla anguilla)
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Many exploited fish species are threatened with collapse and the European eel is no exception. Its abundance has declined dramatically and various reasons account for this, among them the introduction of the invasive swim bladder nematode Anguillicola crassus. For developing an adequate immune response against this parasite, variation at the genes of the major histocompatibility complex (MHC), a key component of the adaptive immune system, might be essential and assessing their diversity might provide critical information for improving conservation strategies. Here, we characterized the MHC class II of the European eel. We provide evidence for relatively high diversity at both MHC IIA and MHC IIB, which contrasts with findings for other endangered species. Furthermore, both genes show signs of site-specific positive selection. The absence of overall positive selection at MHC IIB might, however, suggests that demographic shifts have negatively impacted that gene, thereby possibly reducing the adaptive potential of the European eel.
KeywordsMajor histocompatibility complex European eel Positive selection Demography
The authors would like to thank E. Prigge for providing the animals, K. Beining for support in the laboratory, and F. Chain for support with the analyses. Furthermore, we thank M. Hofmann for fruitful discussions and T. Lenz for valuable comments on a previous version of the manuscript. MBS is supported by the International Max Planck Research School for Evolutionary Biology. CE is supported by the German Science Foundation (DFG grant EI841/4-1 and EI841/6-1). The work was further rendered possible thanks to a small grant from the Fisheries Society of the British Isles.
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Conflict of interest
The authors declare that they have no conflict of interest.
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