Genetic diversity is fundamental to maintaining the long‐term viability of populations, yet reduced genetic variation is often associated with small, isolated populations. To examine the relationship between demography and genetic variation, variation at hypervariable loci (e.g., microsatellite DNA loci) is often measured. However, these loci are selectively neutral (or near neutral) and may not accurately reflect genomewide variation. Variation at functional trait loci, such as the major histocompatibility complex (MHC), can provide a better assessment of adaptive genetic variation in fragmented populations. We compared patterns of microsatellite and MHC variation across three Eastern Massasauga (Sistrurus catenatus) populations representing a gradient of demographic histories to assess the relative roles of natural selection and genetic drift. Using 454 deep amplicon sequencing, we identified 24 putatively functional MHC IIB exon 2 alleles belonging to a minimum of six loci. Analysis of synonymous and nonsynonymous substitution rates provided evidence of historical positive selection at the nucleotide level, and Tajima's D provided support for balancing selection in each population. As predicted, estimates of microsatellite allelic richness, observed, heterozygosity, and expected heterozygosity varied among populations in a pattern qualitatively consistent with demographic history and abundance. While MHC allelic richness at the population and individual levels revealed similar trends, MHC nucleotide diversity was unexpectedly high in the smallest population. Overall, these results suggest that genetic variation in the Eastern Massasauga populations in Illinois has been shaped by multiple evolutionary mechanisms. Thus, conservation efforts should consider both neutral and functional genetic variation when managing captive and wild Eastern Massasauga populations.
Jaeger, Collin P.; Duvall, Marvin R.; Swanson, Bradley J.; Phillips, Christopher A.; Dreslik, Michael J.; Baker, Sarah J.; and King, Richard B., "Microsatellite and major histocompatibility complex variation in an endangered rattlesnake, the Eastern Massasauga (Sistrurus catenatus)" (2016). Faculty Peer-Reviewed Publications. 762.
Department of Biological Sciences
NIU Library Open Access Grant Department of Biological Sciences at Northern Illinois University We thank M. Redmer for providing tissue samples from Cook County, A. Stedman and R. Hoffman for their valuable assistance in the lab, and three anonymous reviewers' comments on an earlier version of this manuscript. This work was funded by grants to R.B.K. from the Department of Biological Sciences at Northern Illinois University. Protocols were approved by the University of Illinois Urbana-Champaign IACUC (protocol 99283, 02010, 04311, 08019, 10238, 13007, 14000) and Northern Illinois University IACUC (protocol LA10-0011).
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© 2016 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.