High major histocompatibility complex class I polymorphism despite bottlenecks in wild and domesticated populations of the zebra finch (Taeniopygia guttata)

ECU Author/Contributor (non-ECU co-authors, if there are any, appear on document)

Daniel J.,Balakrishnan,Christopher N. Newhouse (Creator)

Institution

East Carolina University (ECU )

Web Site: http://www.ecu.edu/lib/

Abstract: Background: Two subspecies of zebra finch, Taeniopygia guttata castanotis and T. g. guttata are native to Australia andthe Lesser Sunda Islands, respectively. The Australian subspecies has been domesticated and is now an importantmodel system for research. Both the Lesser Sundan subspecies and domesticated Australian zebra finches haveundergone population bottlenecks in their history, and previous analyses using neutral markers have reported reducedneutral genetic diversity in these populations. Here we characterize patterns of variation in the third exon of the highlyvariable major histocompatibility complex (MHC) class I a chain. As a benchmark for neutral divergence, we also reportthe first mitochondrial NADH dehydrogenase 2 (ND2) sequences in this important model system.Results: Despite natural and human-mediated population bottlenecks, we find that high MHC class I polymorphismpersists across all populations. As expected, we find higher levels of nucleotide diversity in the MHC locus relative toneutral loci, and strong evidence of positive selection acting on important residues forming the peptide-binding region(PBR). Clear population differentiation of MHC allele frequencies is also evident, and this may be due to adaptation tonew habitats and associated pathogens and/or genetic drift. Whereas the MHC Class I locus shows broad haplotypesharing across populations, ND2 is the first locus surveyed to date to show reciprocal monophyly of the two subspecies.Conclusions: Despite genetic bottlenecks and genetic drift, all surveyed zebra finch populations have maintained highMHC Class I diversity. The diversity at the MHC Class I locus in the Lesser Sundan subspecies contrasts sharply with thelack of diversity in previously examined neutral loci, and may thus be a result of selection acting to maintainpolymorphism. Given uncertainty in historical population demography, however, it is difficult to rule out neutralprocesses in maintaining the observed diversity. The surveyed populations also differ in MHC Class I allele frequencies,and future studies are needed to assess whether these changes result in functional immune differences

Additional Information

Publication

Other

Language: English

Date: 2015

Keywords

Bottleneck, Immune, ND2, Positive selection, Genetic drift, Evolution

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