Drift rather than selection dominates MHC class II allelic diversity patterns at the biogeographical range scale in natterjack toads Bufo calamita

PLoS One. 2014 Jun 17;9(6):e100176. doi: 10.1371/journal.pone.0100176. eCollection 2014.


Study of major histocompatibility complex (MHC) loci has gained great popularity in recent years, partly due to their function in protecting vertebrates from infections. This is of particular interest in amphibians on account of major threats many species face from emergent diseases such as chytridiomycosis. In this study we compare levels of diversity in an expressed MHC class II locus with neutral genetic diversity at microsatellite loci in natterjack toad (Bufo (Epidalea) calamita) populations across the whole of the species' biogeographical range. Variation at both classes of loci was high in the glacial refugium areas (REF) and much lower in postglacial expansion areas (PGE), especially in range edge populations. Although there was clear evidence that the MHC locus was influenced by positive selection in the past, congruence with the neutral markers suggested that historical demographic events were the main force shaping MHC variation in the PGE area. Both neutral and adaptive genetic variation declined with distance from glacial refugia. Nevertheless, there were also some indications from differential isolation by distance and allele abundance patterns that weak effects of selection have been superimposed on the main drift effect in the PGE zone.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alleles
  • Amino Acid Sequence
  • Animals
  • Bufonidae
  • Genetic Drift*
  • Genetic Variation / genetics*
  • Genetics, Population*
  • Geography
  • Histocompatibility Antigens Class II / genetics*
  • Microsatellite Repeats / genetics*
  • Molecular Sequence Data
  • Phylogeny
  • Selection, Genetic / genetics*
  • Sequence Homology, Amino Acid


  • Histocompatibility Antigens Class II

Grant support

This research was funded by the Leverhulme trust (http://www.leverhulme.ac.uk). Grant number: F/00230/AH. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.