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Biedrzycka A, O'Connor E, Sebastian A, Migalska M, Radwan J, Zając T, Bielański W, Solarz W, Ćmiel A, Westerdahl H. Extreme MHC class I diversity in the sedge warbler (Acrocephalus schoenobaenus); selection patterns and allelic divergence suggest that different genes have different functions. BMC Evol Biol 2017; 17:159. [PMID: 28679358 PMCID: PMC5497381 DOI: 10.1186/s12862-017-0997-9] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2016] [Accepted: 06/14/2017] [Indexed: 11/23/2022] Open
Abstract
Background Recent work suggests that gene duplications may play an important role in the evolution of immunity genes. Passerine birds, and in particular Sylvioidea warblers, have highly duplicated major histocompatibility complex (MHC) genes, which are key in immunity, compared to other vertebrates. However, reasons for this high MHC gene copy number are yet unclear. High-throughput sequencing (HTS) allows MHC genotyping even in individuals with extremely duplicated genes. This HTS data can reveal evidence of selection, which may help to unravel the putative functions of different gene copies, i.e. neofunctionalization. We performed exhaustive genotyping of MHC class I in a Sylvioidea warbler, the sedge warbler, Acrocephalus schoenobaenus, using the Illumina MiSeq technique on individuals from a wild study population. Results The MHC diversity in 863 genotyped individuals by far exceeds that of any other bird species described to date. A single individual could carry up to 65 different alleles, a large proportion of which are expressed (transcribed). The MHC alleles were of three different lengths differing in evidence of selection, diversity and divergence within our study population. Alleles without any deletions and alleles containing a 6 bp deletion showed characteristics of classical MHC genes, with evidence of multiple sites subject to positive selection and high sequence divergence. In contrast, alleles containing a 3 bp deletion had no sites subject to positive selection and had low divergence. Conclusions Our results suggest that sedge warbler MHC alleles that either have no deletion, or contain a 6 bp deletion, encode classical antigen presenting MHC molecules. In contrast, MHC alleles containing a 3 bp deletion may encode molecules with a different function. This study demonstrates that highly duplicated MHC genes can be characterised with HTS and that selection patterns can be useful for revealing neofunctionalization. Importantly, our results highlight the need to consider the putative function of different MHC genes in future studies of MHC in relation to disease resistance and fitness. Electronic supplementary material The online version of this article (doi:10.1186/s12862-017-0997-9) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Aleksandra Biedrzycka
- Institute of Nature Conservation, Polish Academy of Sciences, Al. Mickiewicza 33, 31-120, Kraków, Poland.
| | - Emily O'Connor
- Molecular Ecology and Evolution Lab, Department of Biology, Lund University, Ecology Building, Sölvegatan 37, 223 62, Lund, Sweden
| | - Alvaro Sebastian
- Evolutionary Biology Group, Faculty of Biology, Adam Mickiewicz University in Poznań, ul. Umultowska 89, 61-614, Poznań, Poland
| | - Magdalena Migalska
- Evolutionary Biology Group, Faculty of Biology, Adam Mickiewicz University in Poznań, ul. Umultowska 89, 61-614, Poznań, Poland
| | - Jacek Radwan
- Evolutionary Biology Group, Faculty of Biology, Adam Mickiewicz University in Poznań, ul. Umultowska 89, 61-614, Poznań, Poland
| | - Tadeusz Zając
- Institute of Nature Conservation, Polish Academy of Sciences, Al. Mickiewicza 33, 31-120, Kraków, Poland
| | - Wojciech Bielański
- Institute of Nature Conservation, Polish Academy of Sciences, Al. Mickiewicza 33, 31-120, Kraków, Poland
| | - Wojciech Solarz
- Institute of Nature Conservation, Polish Academy of Sciences, Al. Mickiewicza 33, 31-120, Kraków, Poland
| | - Adam Ćmiel
- Institute of Nature Conservation, Polish Academy of Sciences, Al. Mickiewicza 33, 31-120, Kraków, Poland
| | - Helena Westerdahl
- Molecular Ecology and Evolution Lab, Department of Biology, Lund University, Ecology Building, Sölvegatan 37, 223 62, Lund, Sweden
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