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Abstract PremiseEvolutionary theory predicts polymorphism should be rare; however, intraspecific variation in floral color is common and can be attributed to genetic drift, plasticity, or variable selection. Examining floral color polymorphism both within contact zones and across a species' range can reveal the mechanisms maintaining this variation. Here, we used a multistep approach to investigate spatially heterogeneous variation in floral bract color inCastilleja coccinea. MethodsWe compared frequencies of color morphs, floral morphology, fitness, and genetic structure in regional populations and in a common garden. Next, we examined habitat differences, including edaphic factors, as potential drivers of variation. Lastly, we leveraged herbarium and iNaturalist occurrence data to investigate whether patterns were consistent at the landscape scale. ResultsBract color inC. coccineais genetically heritable, with yellow dominant over red, and is under selection. Populations are predominantly monomorphic, with color distance showing no correlation to genetic or geographic distance, despite significant genetic isolation by distance. Yellow morphs were associated with open wetlands, while red morphs occurred at drier sites with nearby tree cover. Red morphs demonstrated lower fitness in a common garden, suggesting trade‐offs associated with pleiotropic effects of floral color. ConclusionsDifferences in floral color between morphs are consistent with diversification associated with a shift in ecological niche. We identified variation in edaphic and habitat conditions as probable drivers of divergence in floral color. Additionally, variation in other floral traits suggests a combined role of pollinators and habitat differences acting in concert to maintain distinct floral color morphs.
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Patterns of genetic variation in a prairie wildflower, Silphium integrifolium , suggest a non‐prairie origin and locally adaptive variation
PREMISEUnderstanding the relationship between genetic structure and geography provides information about a species’ history and can be used for breeding and conservation goals. The North American prairie is interesting because of its recent origin and subsequent fragmentation.Silphium integrifolium, an iconic perennial American prairie wildflower, is targeted for domestication, having undergone a few generations of improvement. We present the first application of population genetic data in this species to address the following goals: (1) improve breeding by characterizing genetic structure and (2) identify the species geographic origin and potential targets and drivers of selection during range expansion. METHODSWe developed a reference transcriptome as a genotyping reference for samples from throughout the species range. Population genetic analyses were used to describe patterns of genetic variation, and demographic modeling was used to characterize potential processes that shaped variation. Outlier scans for selection and associations with environmental variables were used to identify loci linked to putative targets and drivers of selection. RESULTSGenetic variation partitioned samples into three geographic clusters. Patterns of variation and demographic modeling suggest that the species origin is in the American Southeast. Breeding program accessions are from the region with lowest observed genetic variation. CONCLUSIONSThis prairie species did not originate within the prairie. Breeding may be improved by including accessions from outside of the germplasm founding region. The geographic structuring and the identified targets and drivers of adaptation can guide collecting efforts toward populations with beneficial agronomic traits.
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- Award ID(s):
- 1737827
- PAR ID:
- 10454312
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- American Journal of Botany
- Volume:
- 108
- Issue:
- 1
- ISSN:
- 0002-9122
- Page Range / eLocation ID:
- p. 145-158
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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