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. 2015 May;24(9):2194-211.
doi: 10.1111/mec.13044. Epub 2015 Jan 21.

Quantitative Trait Locus Mapping Identifies Candidate Alleles Involved in Adaptive Introgression and Range Expansion in a Wild Sunflower

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Free PMC article

Quantitative Trait Locus Mapping Identifies Candidate Alleles Involved in Adaptive Introgression and Range Expansion in a Wild Sunflower

Kenneth D Whitney et al. Mol Ecol. .
Free PMC article

Abstract

The wild North American sunflowers Helianthus annuus and H. debilis are participants in one of the earliest identified examples of adaptive trait introgression, and the exchange is hypothesized to have triggered a range expansion in H. annuus. However, the genetic basis of the adaptive exchange has not been examined. Here, we combine quantitative trait locus (QTL) mapping with field measurements of fitness to identify candidate H. debilis QTL alleles likely to have introgressed into H. annuus to form the natural hybrid lineage H. a. texanus. Two 500-individual BC1 mapping populations were grown in central Texas, genotyped for 384 single nucleotide polymorphism (SNP) markers and then phenotyped in the field for two fitness and 22 herbivore resistance, ecophysiological, phenological and architectural traits. We identified a total of 110 QTL, including at least one QTL for 22 of the 24 traits. Over 75% of traits exhibited at least one H. debilis QTL allele that would shift the trait in the direction of the wild hybrid H. a. texanus. We identified three chromosomal regions where H. debilis alleles increased both female and male components of fitness; these regions are expected to be strongly favoured in the wild. QTL for a number of other ecophysiological, phenological and architectural traits colocalized with these three regions and are candidates for the actual traits driving adaptive shifts. G × E interactions played a modest role, with 17% of the QTL showing potentially divergent phenotypic effects between the two field sites. The candidate adaptive chromosomal regions identified here serve as explicit hypotheses for how the genetic architecture of the hybrid lineage came into existence.

Keywords: adaptive trait introgression; herbivory; hybridization; invasion; phenology; plant architecture; quantitative trait locus; range expansion; seed predation; single nucleotide polymorphism.

Figures

Fig. 1
Fig. 1
Partial Quantitative Trait Locus (QTL) map for H. annuus x H. debilis BC1 hybrids grown in the field in central Texas. Linkage groups lacking QTL that affect fitness traits are not shown (see Fig. S1 for full map). Loci affecting fitness traits are shown in Red and co-localizing trait QTL are shown in Black. Marker names are shown to the right of the linkage group; marker positions (cM) are shown to the left. Solid bars indicate the QTL position +/− 0.5 cM, while thin capped lines indicate the +/− 1-LOD support interval. Additive effects of the H. debilis allele are shown in parentheses following the trait name; effect sizes have been back-transformed for traits subject to square-root transformation (see Table 1). Separate additive effects (for the BFL and LBJ sites, respectively) are displayed for loci showing significant QTL × Site interactions.
Fig. 1
Fig. 1
Partial Quantitative Trait Locus (QTL) map for H. annuus x H. debilis BC1 hybrids grown in the field in central Texas. Linkage groups lacking QTL that affect fitness traits are not shown (see Fig. S1 for full map). Loci affecting fitness traits are shown in Red and co-localizing trait QTL are shown in Black. Marker names are shown to the right of the linkage group; marker positions (cM) are shown to the left. Solid bars indicate the QTL position +/− 0.5 cM, while thin capped lines indicate the +/− 1-LOD support interval. Additive effects of the H. debilis allele are shown in parentheses following the trait name; effect sizes have been back-transformed for traits subject to square-root transformation (see Table 1). Separate additive effects (for the BFL and LBJ sites, respectively) are displayed for loci showing significant QTL × Site interactions.

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