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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

Phylogenetic tree of anuran exon 2 MHC class II nucleotide sequences.A: Multispecies comparisons using 157 bp of sequence. Triturus (Trcr) and Ambystoma (Amti) sequences were used as outgroups. Genbank accession numbers are given in brackets. B: B. calamita alleles with Xenopus outgroup using 282 bp of sequence. Filled circles, alleles only found in the PGE; open circles, alleles only found in SW France and PGE. Remaining alleles were only found in the REF populations. A ML bootstrap consensus tree from 1000 replicates [82] was constructed in Mega 5 [60]. The evolutionary distances were computed using the Kimura 2-parameter method [71]. Only bootstrap values above 50% are shown.
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pone-0100176-g003: Phylogenetic tree of anuran exon 2 MHC class II nucleotide sequences.A: Multispecies comparisons using 157 bp of sequence. Triturus (Trcr) and Ambystoma (Amti) sequences were used as outgroups. Genbank accession numbers are given in brackets. B: B. calamita alleles with Xenopus outgroup using 282 bp of sequence. Filled circles, alleles only found in the PGE; open circles, alleles only found in SW France and PGE. Remaining alleles were only found in the REF populations. A ML bootstrap consensus tree from 1000 replicates [82] was constructed in Mega 5 [60]. The evolutionary distances were computed using the Kimura 2-parameter method [71]. Only bootstrap values above 50% are shown.

Mentions: Amphibian MHC class II exon 2 sequences formed some strongly supported clusters (Figure 3A). Rana, Xenopus and Discoglossoidea (Bombina and Alytes species) sequences all formed separate groups. Within those groups there was also strong support for some branches separating species. The Central American Sachatamia and Espadarana clustered strongly with the European Bufo. Both the phylogenetic network (Figure S1) and the tree (Figure 3B) produced congruent results for the B. calamita MHC class II B locus.


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)

Phylogenetic tree of anuran exon 2 MHC class II nucleotide sequences.A: Multispecies comparisons using 157 bp of sequence. Triturus (Trcr) and Ambystoma (Amti) sequences were used as outgroups. Genbank accession numbers are given in brackets. B: B. calamita alleles with Xenopus outgroup using 282 bp of sequence. Filled circles, alleles only found in the PGE; open circles, alleles only found in SW France and PGE. Remaining alleles were only found in the REF populations. A ML bootstrap consensus tree from 1000 replicates [82] was constructed in Mega 5 [60]. The evolutionary distances were computed using the Kimura 2-parameter method [71]. Only bootstrap values above 50% are shown.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0100176-g003: Phylogenetic tree of anuran exon 2 MHC class II nucleotide sequences.A: Multispecies comparisons using 157 bp of sequence. Triturus (Trcr) and Ambystoma (Amti) sequences were used as outgroups. Genbank accession numbers are given in brackets. B: B. calamita alleles with Xenopus outgroup using 282 bp of sequence. Filled circles, alleles only found in the PGE; open circles, alleles only found in SW France and PGE. Remaining alleles were only found in the REF populations. A ML bootstrap consensus tree from 1000 replicates [82] was constructed in Mega 5 [60]. The evolutionary distances were computed using the Kimura 2-parameter method [71]. Only bootstrap values above 50% are shown.
Mentions: Amphibian MHC class II exon 2 sequences formed some strongly supported clusters (Figure 3A). Rana, Xenopus and Discoglossoidea (Bombina and Alytes species) sequences all formed separate groups. Within those groups there was also strong support for some branches separating species. The Central American Sachatamia and Espadarana clustered strongly with the European Bufo. Both the phylogenetic network (Figure S1) and the tree (Figure 3B) produced congruent results for the B. calamita MHC class II B locus.

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