Drift and selection influence geographic variation at immune loci of prairie-chickens

Previous studies of immunity in wild populations have focused primarily on genes of the major histocompatibility complex (MHC); however, studies of model species have identified additional immune‐related genes that also affect fitness. In this study, we sequenced five non‐MHC immune genes in six gre...

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Bibliographic Details
Published in:Molecular ecology 2011-11, Vol.20 (22), p.4695-4706
Main Authors: BOLLMER, JENNIFER L., RUDER, ELIZABETH A., JOHNSON, JEFF A., EIMES, JOHN A., DUNN, PETER O.
Format: Article
Language:English
Subjects:
Animals
Biological variation
Ecology
Galliformes - genetics
Galliformes - immunology
Genetic diversity
Genetic Drift
Genetic Variation
Genetics, Population
Geography
grouse
Haplotypes
immunity
Microsatellite Repeats
selection
Selection, Genetic
Sequence Analysis, DNA
single-nucleotide polymorphism
Tympanuchus cupido
Wildfowl
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Summary:Previous studies of immunity in wild populations have focused primarily on genes of the major histocompatibility complex (MHC); however, studies of model species have identified additional immune‐related genes that also affect fitness. In this study, we sequenced five non‐MHC immune genes in six greater prairie‐chicken (Tympanuchus cupido) populations that have experienced varying degrees of genetic drift as a consequence of population bottlenecks and fragmentation. We compared patterns of geographic variation at the immune genes with six neutral microsatellite markers to investigate the relative effects of selection and genetic drift. Global FST outlier tests identified positive selection on just one of five immune genes (IAP‐1) in one population. In contrast, at other immune genes, standardized G′ST values were lower than those at microsatellites for a majority of pairwise population comparisons, consistent with balancing selection or with species‐wide positive or purifying selection resulting in similar haplotype frequencies across populations. The effects of genetic drift were also evident as summary statistics (e.g., Tajima’s D) did not differ from neutrality for the majority of cases, and immune gene diversity (number of haplotypes per gene) was correlated positively with population size. In summary, we found that both genetic drift and selection shaped variation at the five immune genes, and the strength and type of selection varied among genes. Our results caution that neutral forces, such as drift, can make it difficult to detect current selection on genes.
ISSN:0962-1083
1365-294X
DOI:10.1111/j.1365-294X.2011.05319.x