Abstract
Hybridization is an important evolutionary force that acts in both constructive and destructive ways. It can both swamp out rare species and create new ones. To better understand these effects I studied hybridization within the sunflower genus Helianthus from three angles. First, I used a rich literature of artificial crossing experiments in Helianthus and Madiinae to ask how fast reproductive isolation evolves and what features affect its accumulation. I show that hybrid sterility can evolve quickly and is faster in annuals than in perennials. I then examine a classic case of introgression involving Helianthus bolanderi. I use modern genomic tools to show that it is not of hybrid origin and likely not a separate species from its congener H. exilis. We do however find introgression with the invading species, H. annuus. In agreement with theory, we find that gene flow is mainly into the invading species. Lastly, I use transcriptomic data for three established homoploid hybrid species, H. anomalus, H. deserticola, and H. paradoxus, and their parents H. annuus and H. petiolaris to map the genomic composition of hybrid species. I show that composition is even or biased towards H. petiolaris. Hybrid genomes are highly recombined but are more similar in genomic composition than expected by chance, suggesting the work of selection. Furthermore, although analyses of genetic distance between the hybrid species and their parents suggests that the hybrids are older than previously appreciated, they do not appear to be fully stabilized. Lastly two of the species, H. anomalus and H. deserticola, may share a common origin. Future directions include mapping introgression in H. annuus, and modeling parental block size to determine the number of loci and strength of selection during hybrid speciation.
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Claims 11
Claim · model-written summary
Hybrid sterility evolved quickly and faster in annuals than perennials.
- Taxon
- Helianthus and Madiinae
HelianthusMadiinaee1 - Outcome
- hybrid sterilitye0
- Direction
- fastere0
- Comparator
- perennialse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“hybrid sterility can evolve quickly and is faster in annuals than in perennials”
e1“artificial crossing experiments in Helianthus and Madiinae”
Claim · model-written summary
Helianthus bolanderi was not supported as a hybrid-origin species.
- Taxon
- Helianthus bolanderiHelianthus bolanderie0
- Outcome
- not of hybrid origine0
Not reportedDirection
Verbatim
e0“Helianthus bolanderi. I use modern genomic tools to show that it is not of hybrid origin”
Claim · model-written summary
Helianthus bolanderi was likely not separate from H. exilis.
- Taxon
- Helianthus bolanderiHelianthus bolanderie0
- Outcome
- likely not a separate species from its congener H. exilise0
Not reportedDirection
Verbatim
e0“Helianthus bolanderi. I use modern genomic tools to show that it is not of hybrid origin and likely not a separate species from its congener H. exilis”
Claim · model-written summary
Introgression with invading H. annuus was found.
- Taxon
- Helianthus bolanderiHelianthus bolanderie1
- Outcome
- introgression with the invading species, H. annuuse0
Not reportedDirection
Verbatim
e0“We do however find introgression with the invading species, H. annuus”
e1“Helianthus bolanderi”
Claim · model-written summary
Gene flow mainly entered the invading species.
- Taxon
- H. annuus
Helianthus annuuse1 - Outcome
- gene flow is mainly into the invading speciese0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“gene flow is mainly into the invading species”
e1“invading species, H. annuus”
Claim · model-written summary
Hybrid species genome composition was even or biased toward H. petiolaris.
- Taxon
- H. anomalus, H. deserticola, and H. paradoxus
Helianthus anomalus
Helianthus deserticola
Helianthus paradoxuse1 - Outcome
- compositione0
- Direction
- biased towardse0
- Comparator
- H. petiolarise0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“composition is even or biased towards H. petiolaris”
e1“three established homoploid hybrid species, H. anomalus, H. deserticola, and H. paradoxus”
Claim · model-written summary
Hybrid genomes were highly recombined.
- Taxon
- H. anomalus, H. deserticola, and H. paradoxusHelianthus anomalusHelianthus deserticolaHelianthus paradoxuse1
- Outcome
- Hybrid genomes are highly recombinede0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Hybrid genomes are highly recombined”
e1“H. anomalus, H. deserticola, and H. paradoxus”
Claim · model-written summary
Hybrid genomes were more compositionally similar than expected by chance.
- Taxon
- H. anomalus, H. deserticola, and H. paradoxusHelianthus anomalusHelianthus deserticolaHelianthus paradoxuse1
- Outcome
- genomic compositione0
- Direction
- more similare0
- Comparator
- expected by chancee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“more similar in genomic composition than expected by chance”
e1“H. anomalus, H. deserticola, and H. paradoxus”
Claim · model-written summary
Genetic distance suggested the hybrid species were older than previously thought.
- Taxon
- H. anomalus, H. deserticola, and H. paradoxusHelianthus anomalusHelianthus deserticolaHelianthus paradoxuse1
- Outcome
- hybrids are oldere0
- Direction
- oldere0
- Comparator
- previously appreciatede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the hybrids are older than previously appreciated”
e1“H. anomalus, H. deserticola, and H. paradoxus”
Claim · model-written summary
The hybrid species did not appear fully stabilized.
- Taxon
- H. anomalus, H. deserticola, and H. paradoxusHelianthus anomalusHelianthus deserticolaHelianthus paradoxuse1
- Outcome
- do not appear to be fully stabilizede0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“they do not appear to be fully stabilized”
e1“H. anomalus, H. deserticola, and H. paradoxus”
Claim · model-written summary
H. anomalus and H. deserticola may share a common origin.
- Taxon
- H. anomalus and H. deserticolaHelianthus anomalusHelianthus deserticolae0
- Outcome
- may share a common origine0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“H. anomalus and H. deserticola, may share a common origin”