Abstract
Sunflowers of the genus Helianthus are models for hybridization research and contain three of the best-studied examples of homoploid hybrid speciation. To understand a broader picture of hybridization within the annual sunflowers, we used whole-genome resequencing to conduct a phylogenomic analysis and test for gene flow between lineages. We find that all annual sunflower species tested have evidence of admixture, suggesting hybridization was common during the radiation of the genus. Support for the major species tree decreases with increasing recombination rate, consistent with hybridization and introgression contributing to discordant topologies. Admixture graphs found hybridization to be associated with the origins of the three putative hybrid species (Helianthus anomalus, Helianthus deserticola, and Helianthus paradoxus). However, the hybridization events are more ancient than suggested by previous work. Furthermore, H. anomalus and H. deserticola appear to have arisen from a single hybridization event involving an unexpected donor, rather than through multiple independent events as previously proposed. This means our results are consistent with, but not definitive proof of, two ancient independent homoploid hybrid speciation events in the genus. Using a broader data set that covers the whole Helianthus genus, including perennial species, we find that signals of introgression span the genus and beyond, suggesting highly divergent introgression and/or the sorting of ancient haplotypes. Thus, Helianthus can be viewed as a syngameon in which largely reproductively isolated species are linked together by occasional or frequent gene flow.
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Claims 7
Claim · model-written summary
All tested annual sunflower species show admixture.
Verbatim
e0“all annual sunflower species tested have evidence of admixture”
Claim · model-written summary
Support for the major species tree falls as recombination rate rises.
- Taxon
- Helianthus
Helianthust0 - Outcome
- Support for the major species treee0
- Direction
- decreasese0
- Qualifier
- increasing recombination ratee0
Not reportedSetting
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Support for the major species tree decreases with increasing recombination rate”
t0“Re-evaluating Homoploid Reticulate Evolution in Helianthus Sunflowers”
Claim · model-written summary
Hybridization is associated with origins of three putative Helianthus hybrid species.
- Taxon
- Helianthus anomalus, Helianthus deserticola, and Helianthus paradoxus
Helianthus anomalus
Helianthus deserticola
Helianthus paradoxuse0 - Outcome
- hybridization to be associated with the originse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“hybridization to be associated with the origins of the three putative hybrid species (Helianthus anomalus, Helianthus deserticola, and Helianthus paradoxus).”
Claim · model-written summary
The inferred hybridization events are older than previously suggested.
- Taxon
- HelianthusHelianthust0
- Outcome
- hybridization eventse0
- Direction
- more anciente0
- Comparator
- previous worke0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the hybridization events are more ancient than suggested by previous work.”
t0“Re-evaluating Homoploid Reticulate Evolution in Helianthus Sunflowers”
Claim · model-written summary
H. anomalus and H. deserticola appear to derive from one hybridization event involving an unexpected donor.
- Taxon
- H. anomalus and H. deserticolaHelianthus anomalusHelianthus deserticolae0
- Outcome
- arisen from a single hybridization evente0
- Qualifier
- unexpected donore0
- Comparator
- multiple independent eventse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“H. anomalus and H. deserticola appear to have arisen from a single hybridization event involving an unexpected donor, rather than through multiple independent events as previously proposed.”
Claim · model-written summary
The findings are consistent with two ancient independent homoploid hybrid speciation events, without proving them.
- Taxon
- HelianthusHelianthust0
- Outcome
- two ancient independent homoploid hybrid speciation eventse0
- Qualifier
- not definitive proofe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“consistent with, but not definitive proof of, two ancient independent homoploid hybrid speciation events in the genus.”
t0“Re-evaluating Homoploid Reticulate Evolution in Helianthus Sunflowers”
Claim · model-written summary
Signals of introgression extend across and beyond Helianthus.
- Taxon
- HelianthusHelianthust0
- Outcome
- signals of introgressione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“signals of introgression span the genus and beyond”
t0“Re-evaluating Homoploid Reticulate Evolution in Helianthus Sunflowers”