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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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Related in: MedlinePlus

Relationships of pairwise FST and distance estimates.Microsatellite data are represented by open circles and MHC data by filled circles.
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pone-0100176-g005: Relationships of pairwise FST and distance estimates.Microsatellite data are represented by open circles and MHC data by filled circles.

Mentions: Pairwise FST comparisons among populations indicated significant population differentiation between 128 of the 136 population comparisons for MHC loci and between all but three for the microsatellite data (see Table S1). Using Mantel tests, pairwise FST and DEST were significantly intercorrelated both for MHC and microsatellite loci for the PGE region including SW France (MHC: rs = 0.6372, n = 105, P<0.0001; microsatellite: rs = 0.2548, n = 105, P = 0.0089). However, in several cases where geographical separation was high, MHC DEST = 1 thus providing incomplete resolution of differentiation level. Subsequent comparisons therefore focused on pairwise FST estimates which were correlated between MHC and microsatellite loci (rs = 0.3128, n = 105, P = 0.0012). Excluding Iberian populations, among areas analysed for both microsatellites and MHC genotypes and not separated by seawater (n = 8; Bordeaux, SW France; Zurich, Switzerland; Carnac, France; Penmarch, France; Cherbourg, France; Halle, Germany; Bukowno/Bielowieza, Poland; Parnu, Estonia), the correlation between MHC and microsatellite pairwise FST estimates was also strong (rs = 0.432, P = 0.025). Mean pairwise FST estimates in this region were similar for both types of loci (0.428 for microsatellites, 0.487 for MHC) and there was significant isolation by distance (IBD, P<0.0001 in both cases). However, the strength of IBD was greater for MHC than for microsatellites as shown using untransformed FST and distance estimates in Figure 5. Regression slopes for the two loci were significantly different (F = 6.14, P = 0.0165). This strongly indicates a role of selection in shaping MHC diversity, as the effects of drift on microsatellite FST estimates are expected to be greater than those on MHC loci, due to their higher mutation rates.


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)

Relationships of pairwise FST and distance estimates.Microsatellite data are represented by open circles and MHC data by filled circles.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0100176-g005: Relationships of pairwise FST and distance estimates.Microsatellite data are represented by open circles and MHC data by filled circles.
Mentions: Pairwise FST comparisons among populations indicated significant population differentiation between 128 of the 136 population comparisons for MHC loci and between all but three for the microsatellite data (see Table S1). Using Mantel tests, pairwise FST and DEST were significantly intercorrelated both for MHC and microsatellite loci for the PGE region including SW France (MHC: rs = 0.6372, n = 105, P<0.0001; microsatellite: rs = 0.2548, n = 105, P = 0.0089). However, in several cases where geographical separation was high, MHC DEST = 1 thus providing incomplete resolution of differentiation level. Subsequent comparisons therefore focused on pairwise FST estimates which were correlated between MHC and microsatellite loci (rs = 0.3128, n = 105, P = 0.0012). Excluding Iberian populations, among areas analysed for both microsatellites and MHC genotypes and not separated by seawater (n = 8; Bordeaux, SW France; Zurich, Switzerland; Carnac, France; Penmarch, France; Cherbourg, France; Halle, Germany; Bukowno/Bielowieza, Poland; Parnu, Estonia), the correlation between MHC and microsatellite pairwise FST estimates was also strong (rs = 0.432, P = 0.025). Mean pairwise FST estimates in this region were similar for both types of loci (0.428 for microsatellites, 0.487 for MHC) and there was significant isolation by distance (IBD, P<0.0001 in both cases). However, the strength of IBD was greater for MHC than for microsatellites as shown using untransformed FST and distance estimates in Figure 5. Regression slopes for the two loci were significantly different (F = 6.14, P = 0.0165). This strongly indicates a role of selection in shaping MHC diversity, as the effects of drift on microsatellite FST estimates are expected to be greater than those on MHC loci, due to their higher mutation rates.

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