TY - JOUR
T1 - Purifying selection does not drive signatures of convergent local adaptation of lodgepole pine and interior spruce
AU - Lu, Mengmeng
AU - Hodgins, Kathryn A.
AU - Degner, Jon C.
AU - Yeaman, Sam
PY - 2019/5/28
Y1 - 2019/5/28
N2 - Background: Lodgepole pine (Pinus contorta) and interior spruce (Picea glauca, Picea engelmannii, and their hybrids) are distantly related conifer species. Previous studies identified 47 genes containing variants associated with environmental variables in both species, providing evidence of convergent local adaptation. However, if the intensity of purifying selection varies with the environment, clines in nucleotide diversity could evolve through linked (background) selection that would yield allele frequency-environment signatures resembling local adaptation. If similar geographic patterns in the strength of purifying selection occur in these species, this could result in the convergent signatures of local adaptation, especially if the landscape of recombination is conserved. In the present study, we investigated whether spatially/environmentally varying purifying selection could give rise to the convergent signatures of local adaptation that had previously reported. Results: We analyzed 86 lodgepole pine and 50 interior spruce natural populations spanning heterogeneous environments in western Canada where previous analyses had found signatures of convergent local adaptation. We estimated nucleotide diversity and Tajima's D for each gene within each population and calculated the strength of correlations between nucleotide diversity and environmental variables. Overall, these estimates in the genes with previously identified convergent local adaptation signatures had no similar pattern between pine and spruce. Clines in nucleotide diversity along environmental variables were found for interior spruce, but not for lodgepole pine. In spruce, genes with convergent adaption signatures showed a higher strength of correlations than genes without convergent adaption signatures, but there was no such disparity in pine, which suggests the pattern in spruce may have arisen due to a combination of selection and hybridization. Conclusions: The results rule out purifying/background selection as a driver of convergent local adaption signatures in lodgepole pine and interior spruce.
AB - Background: Lodgepole pine (Pinus contorta) and interior spruce (Picea glauca, Picea engelmannii, and their hybrids) are distantly related conifer species. Previous studies identified 47 genes containing variants associated with environmental variables in both species, providing evidence of convergent local adaptation. However, if the intensity of purifying selection varies with the environment, clines in nucleotide diversity could evolve through linked (background) selection that would yield allele frequency-environment signatures resembling local adaptation. If similar geographic patterns in the strength of purifying selection occur in these species, this could result in the convergent signatures of local adaptation, especially if the landscape of recombination is conserved. In the present study, we investigated whether spatially/environmentally varying purifying selection could give rise to the convergent signatures of local adaptation that had previously reported. Results: We analyzed 86 lodgepole pine and 50 interior spruce natural populations spanning heterogeneous environments in western Canada where previous analyses had found signatures of convergent local adaptation. We estimated nucleotide diversity and Tajima's D for each gene within each population and calculated the strength of correlations between nucleotide diversity and environmental variables. Overall, these estimates in the genes with previously identified convergent local adaptation signatures had no similar pattern between pine and spruce. Clines in nucleotide diversity along environmental variables were found for interior spruce, but not for lodgepole pine. In spruce, genes with convergent adaption signatures showed a higher strength of correlations than genes without convergent adaption signatures, but there was no such disparity in pine, which suggests the pattern in spruce may have arisen due to a combination of selection and hybridization. Conclusions: The results rule out purifying/background selection as a driver of convergent local adaption signatures in lodgepole pine and interior spruce.
KW - Clines
KW - Genetic admixture
KW - Hybridization
KW - Nucleotide diversity
KW - SNP
KW - Tajima's D
UR - http://www.scopus.com/inward/record.url?scp=85066322319&partnerID=8YFLogxK
U2 - 10.1186/s12862-019-1438-8
DO - 10.1186/s12862-019-1438-8
M3 - Article
C2 - 31138118
AN - SCOPUS:85066322319
SN - 1471-2148
VL - 19
JO - BMC Evolutionary Biology
JF - BMC Evolutionary Biology
IS - 1
M1 - 110
ER -