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Neutral Genetic Processes Influence MHC Evolution in Threatened Gopher Tortoises (Gopherus polyphemus)
Jean P Elbers1, Rachel W Clostio1, Sabrina S Taylor1
1School of Renewable Natural Resources, Louisiana State University and AgCenter, 227 RNR Bldg., Baton Rouge, LA 70803; and Department of Biology, University of Louisiana at Lafayette, Lafayette, LA.
The Journal of Heredity
|April 8, 2017
Summary
Gopher tortoises in nonthreatened areas show higher genetic diversity in immune genes (MHC class II) and neutral markers. Evidence suggests positive selection on MHC class II, but genetic drift may impact adaptive alleles.
Area of Science:
- * Evolutionary genetics
- * Conservation biology
- * Immunogenetics
Background:
- * Adaptive genetic variation is crucial for species' response to environmental changes.
- * Neutral genetic markers are often used to infer adaptive variation, but this can be limiting.
- * Major histocompatibility complex (MHC) genes are vital for adaptive immunity and serve as a proxy for adaptive variation.
Purpose of the Study:
- * To compare adaptive genetic variation at MHC genes with neutral genetic variation in gopher tortoises.
- * To assess genetic diversity and selection pressures in threatened versus nonthreatened populations.
- * To investigate historical and recent gene flow and its impact on population connectivity.
Main Methods:
- * Sequencing of MHC class I and class II peptide-binding regions in Gopherus polyphemus populations.
- * Analysis of neutral genetic variation using 10 microsatellite loci.
- * Comparison of genetic diversity metrics (allelic richness, heterozygosity) and population differentiation (Mantel test).
- * Inference of selection (dN/dS ratio) and gene flow (Migrate-N, BayesAss).
Main Results:
- * Higher genetic diversity at MHC class II and microsatellite loci was observed in nonthreatened gopher tortoise populations.
- * MHC class II sequences exhibited evidence of positive selection (dN/dS > 1).
- * Historical gene flow exceeded recent gene flow, indicating past habitat connectivity.
- * MHC and microsatellite genetic differentiation were correlated, suggesting neutral processes influence MHC evolution.
Conclusions:
- * Nonthreatened gopher tortoise populations possess greater adaptive and neutral genetic diversity.
- * Positive selection acts on MHC class II genes, crucial for immune response.
- * Habitat fragmentation has reduced gene flow, potentially impacting adaptive potential.
- * Genetic drift may counteract the fixation of advantageous MHC alleles, particularly in fragmented populations.