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

Zeisset I, Beebee TJ - PLoS ONE (2014)

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: School of Pharmacy and Biomolecular Sciences, University of Brighton, Brighton, United Kingdom; School of Life Sciences, University of Sussex, Brighton, United Kingdom.

ABSTRACT
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.

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Phylogeography of B. calamita populations.Bootstrap values >50% are given for the microsatellite analysis. Sampling site numbers corresponding to Figure 1 are given in brackets.
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pone-0100176-g006: Phylogeography of B. calamita populations.Bootstrap values >50% are given for the microsatellite analysis. Sampling site numbers corresponding to Figure 1 are given in brackets.

Mentions: Phylogeographic trees based on microsatellite and MHC allele frequencies were broadly congruent (Figure 6). However, allele frequencies and distributions in the PGE region were significantly different between the loci (Figure 7). We excluded colour coding for the MHC locus in the Iberian populations from this comparison, as they do not share any alleles with the other populations and contain a large number of population specific alleles. For a full comparison see Table A in File S1 for allele frequencies at all loci in all populations. Certain MHC alleles were common in adjacent geographic areas (e.g Buca B2 in Ireland, UK, Netherlands, Germany and Sweden, Buca B5 in Sweden, Denmark, Estonia, Poland, Switzerland and Germany) (Figure 7A). No such pattern could be discerned for the most polymorphic microsatellite locus Bcalµ3 (Figure 7B).


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

Zeisset I, Beebee TJ - PLoS ONE (2014)

Phylogeography of B. calamita populations.Bootstrap values >50% are given for the microsatellite analysis. Sampling site numbers corresponding to Figure 1 are given in brackets.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4061088&req=5

pone-0100176-g006: Phylogeography of B. calamita populations.Bootstrap values >50% are given for the microsatellite analysis. Sampling site numbers corresponding to Figure 1 are given in brackets.
Mentions: Phylogeographic trees based on microsatellite and MHC allele frequencies were broadly congruent (Figure 6). However, allele frequencies and distributions in the PGE region were significantly different between the loci (Figure 7). We excluded colour coding for the MHC locus in the Iberian populations from this comparison, as they do not share any alleles with the other populations and contain a large number of population specific alleles. For a full comparison see Table A in File S1 for allele frequencies at all loci in all populations. Certain MHC alleles were common in adjacent geographic areas (e.g Buca B2 in Ireland, UK, Netherlands, Germany and Sweden, Buca B5 in Sweden, Denmark, Estonia, Poland, Switzerland and Germany) (Figure 7A). No such pattern could be discerned for the most polymorphic microsatellite locus Bcalµ3 (Figure 7B).

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: School of Pharmacy and Biomolecular Sciences, University of Brighton, Brighton, United Kingdom; School of Life Sciences, University of Sussex, Brighton, United Kingdom.

ABSTRACT
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.

Show MeSH
Related in: MedlinePlus