Reduced MHC and neutral variation in the Galápagos hawk, an island endemic

<p>Abstract</p> <p>Background</p> <p>Genes at the major histocompatibility complex (MHC) are known for high levels of polymorphism maintained by balancing selection. In small or bottlenecked populations, however, genetic drift may be strong enough to overwhelm the effec...

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Main Authors: Ernest Holly B, Hull Joshua M, Bollmer Jennifer L, Sarasola José H, Parker Patricia G
Format: Article
Language:English
Published: BMC 2011-05-01
Series:BMC Evolutionary Biology
Online Access:http://www.biomedcentral.com/1471-2148/11/143
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spelling doaj-6ae4c0fc78b44da78bd2602b269c8bd62021-09-02T04:28:09ZengBMCBMC Evolutionary Biology1471-21482011-05-0111114310.1186/1471-2148-11-143Reduced MHC and neutral variation in the Galápagos hawk, an island endemicErnest Holly BHull Joshua MBollmer Jennifer LSarasola José HParker Patricia G<p>Abstract</p> <p>Background</p> <p>Genes at the major histocompatibility complex (MHC) are known for high levels of polymorphism maintained by balancing selection. In small or bottlenecked populations, however, genetic drift may be strong enough to overwhelm the effect of balancing selection, resulting in reduced MHC variability. In this study we investigated MHC evolution in two recently diverged bird species: the endemic Galápagos hawk (<it>Buteo galapagoensis</it>), which occurs in small, isolated island populations, and its widespread mainland relative, the Swainson's hawk (<it>B. swainsoni</it>).</p> <p>Results</p> <p>We amplified at least two MHC class II B gene copies in each species. We recovered only three different sequences from 32 Galápagos hawks, while we amplified 20 unique sequences in 20 Swainson's hawks. Most of the sequences clustered into two groups in a phylogenetic network, with one group likely representing pseudogenes or nonclassical loci. Neutral genetic diversity at 17 microsatellite loci was also reduced in the Galápagos hawk compared to the Swainson's hawk.</p> <p>Conclusions</p> <p>The corresponding loss in neutral diversity suggests that the reduced variability present at Galápagos hawk MHC class II B genes compared to the Swainson's hawk is primarily due to a founder event followed by ongoing genetic drift in small populations. However, purifying selection could also explain the low number of MHC alleles present. This lack of variation at genes involved in the adaptive immune response could be cause for concern should novel diseases reach the archipelago.</p> http://www.biomedcentral.com/1471-2148/11/143
collection DOAJ
language English
format Article
sources DOAJ
author Ernest Holly B
Hull Joshua M
Bollmer Jennifer L
Sarasola José H
Parker Patricia G
spellingShingle Ernest Holly B
Hull Joshua M
Bollmer Jennifer L
Sarasola José H
Parker Patricia G
Reduced MHC and neutral variation in the Galápagos hawk, an island endemic
BMC Evolutionary Biology
author_facet Ernest Holly B
Hull Joshua M
Bollmer Jennifer L
Sarasola José H
Parker Patricia G
author_sort Ernest Holly B
title Reduced MHC and neutral variation in the Galápagos hawk, an island endemic
title_short Reduced MHC and neutral variation in the Galápagos hawk, an island endemic
title_full Reduced MHC and neutral variation in the Galápagos hawk, an island endemic
title_fullStr Reduced MHC and neutral variation in the Galápagos hawk, an island endemic
title_full_unstemmed Reduced MHC and neutral variation in the Galápagos hawk, an island endemic
title_sort reduced mhc and neutral variation in the galápagos hawk, an island endemic
publisher BMC
series BMC Evolutionary Biology
issn 1471-2148
publishDate 2011-05-01
description <p>Abstract</p> <p>Background</p> <p>Genes at the major histocompatibility complex (MHC) are known for high levels of polymorphism maintained by balancing selection. In small or bottlenecked populations, however, genetic drift may be strong enough to overwhelm the effect of balancing selection, resulting in reduced MHC variability. In this study we investigated MHC evolution in two recently diverged bird species: the endemic Galápagos hawk (<it>Buteo galapagoensis</it>), which occurs in small, isolated island populations, and its widespread mainland relative, the Swainson's hawk (<it>B. swainsoni</it>).</p> <p>Results</p> <p>We amplified at least two MHC class II B gene copies in each species. We recovered only three different sequences from 32 Galápagos hawks, while we amplified 20 unique sequences in 20 Swainson's hawks. Most of the sequences clustered into two groups in a phylogenetic network, with one group likely representing pseudogenes or nonclassical loci. Neutral genetic diversity at 17 microsatellite loci was also reduced in the Galápagos hawk compared to the Swainson's hawk.</p> <p>Conclusions</p> <p>The corresponding loss in neutral diversity suggests that the reduced variability present at Galápagos hawk MHC class II B genes compared to the Swainson's hawk is primarily due to a founder event followed by ongoing genetic drift in small populations. However, purifying selection could also explain the low number of MHC alleles present. This lack of variation at genes involved in the adaptive immune response could be cause for concern should novel diseases reach the archipelago.</p>
url http://www.biomedcentral.com/1471-2148/11/143
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