Habitat divergence between a homoploid hybrid sunflower species,<i>Helianthus paradoxus</i>(Asteraceae), and its progenitors

Welch, Mark E.; Rieseberg, Loren H.

doi:10.3732/ajb.89.3.472

Cited by 82 publications

(108 citation statements)

References 38 publications

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“…This species also has densely pubescent leaves covered with long, silky hairs, exhibits a woody growth habit under certain environmental conditions, and is tolerant of drought conditions and saline soils (Richards 1992;Baldini and Vannozzi 1999). In contrast, wild ANN flowers much earlier in the summer, has less pubescent leaves that are green in appearance, is rarely found in sandy soils, and is typically salt sensitive (Welch and Rieseberg 2002).…”

Section: Discussionmentioning

confidence: 99%

Chromosomal Evolution and Patterns of Introgression inHelianthus

et al. 2014

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Knowledge of the nature and extent of karyotypic differences between species provides insight into the evolutionary history of the genomes in question and, in the case of closely related species, the potential for genetic exchange between taxa. We constructed high-density genetic maps of the silverleaf sunflower (Helianthus argophyllus) and Algodones Dune sunflower (H. niveus ssp. tephrodes) genomes and compared them to a consensus map of cultivated sunflower (H. annuus) to identify chromosomal rearrangements between species. The genetic maps of H. argophyllus and H. niveus ssp. tephrodes included 17 linkage groups each and spanned 1337 and 1478 cM, respectively. Comparative analyses revealed greater divergence between H. annuus and H. niveus ssp. tephrodes (13 inverted segments, 18 translocated segments) than between H. annuus and H. argophyllus (10 inverted segments, 8 translocated segments), consistent with their known phylogenetic relationships. Marker order was conserved across much of the genome, with 83 and 64% of the H. argophyllus and H. niveus ssp. tephrodes genomes, respectively, being syntenic with H. annuus. Population genomic analyses between H. annuus and H. argophyllus, which are sympatric across a portion of the natural range of H. annuus, revealed significantly elevated genetic structure in rearranged portions of the genome, indicating that such rearrangements are associated with restricted gene flow between these two species.C HROMOSOMAL rearrangements are of considerable interest because they are often associated with barriers to gene flow between related species, either due to their direct effects on the fitness of heterozygotes or through the indirect effects of genic barriers embedded within them (White 1978;Barton and Bengtsson 1986;Rieseberg et al. 1995bRieseberg et al. , 1999Rieseberg 2001;Navarro and Barton 2003;Kirkpatrick and Barton 2006; reviewed in Faria and Navarro 2010;Gimenez et al. 2012). As such, detailed information on karyotypic differences between species provides insight into the nature of reproductive isolation and, more pragmatically, informs attempts to introgress beneficial alleles from wild species into crop gene pools (Chetelat and Meglic 2000;Foulongne et al. 2003;Dirlewanger et al. 2004). An improved understanding of synteny across species can also facilitate the identification and localization of functionally important genes in a taxon of interest through the extrapolation of gene order from model species (e.g., Choi et al. 2004;Dilbirligi et al. 2006).The genus Helianthus, which is composed of 49 species native to the Americas (Timme et al. 2007) and includes cultivated sunflower (Helianthus annuus L.; 2n = 2x = 34; hereafter referred to as ANN), has emerged as a model for genetic studies of adaptation, hybridization, and speciation (Rieseberg et al. 1995a,b;Lai et al. 2005;Reagon and Snow 2006;Massinga et al. 2009;Gutierrez et al. 2010;Vekemans 2010;Roumet et al. 2013). Insight into the nature and extent of reproductive barriers within Helianthus will ...

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Section: Discussionmentioning

confidence: 99%

Chromosomal Evolution and Patterns of Introgression inHelianthus

et al. 2014

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“…Unlike mutation, hybridization provides variation at numerous traits simultaneously, which may be critical for evolutionarily difficult steps that require changes at multiple loci. Colonization of discrete and highly divergent habitats, which appears to have been facilitated by hybridization in annual sunflowers (Welch & Rieseberg 2002;Lexer et al 2003a,b), may represent one such step. Of course, hybridization is unlikely to produce useful transgressive phenotypes for traits that already have a continuous history of directional selection in the parental species.…”

Section: Discussionmentioning

confidence: 99%

“…We have argued elsewhere that extreme phenotypes generated by hybridization may play an important part in adaptation and speciation (Rieseberg et al 1999;Welch & Rieseberg 2002). Unlike mutation, hybridization provides variation at numerous traits simultaneously, which may be critical for evolutionarily difficult steps that require changes at multiple loci.…”

Section: Discussionmentioning

confidence: 99%

The genetic architecture necessary for transgressive segregation is common in both natural and domesticated populations

Rieseberg

Widmer

Arntz³

et al. 2003

Phil. Trans. R. Soc. Lond. B

266

256

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Segregating hybrids often exhibit phenotypes that are extreme or novel relative to the parental lines. This phenomenon is referred to as transgressive segregation, and it provides a mechanism by which hybridization might contribute to adaptive evolution. Genetic studies indicate that transgressive segregation typically results from recombination between parental taxa that possess quantitative trait loci (QTLs) with antagonistic effects (i.e. QTLs with effects that are in the opposite direction to parental differences for those traits). To assess whether this genetic architecture is common, we tabulated the direction of allelic effects for 3252 QTLs from 749 traits and 96 studies. Most traits (63.6%) had at least one antagonistic QTL, indicating that the genetic substrate for transgressive segregation is common. Plants had significantly more antagonistic QTLs than animals, which agrees with previous reports that transgressive segregation is more common in plants than in animals. Likewise, antagonistic QTLs were more frequent in intrathan in interspecific crosses and in morphological than in physiological traits. These results indicate that transgressive segregation provides a general mechanism for the production of extreme phenotypes at both above and below the species level and testify to the possible creative part of hybridization in adaptive evolution and speciation.

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“…Three different hybrid species (Helianthus anomalus, Helianthus paradoxus and Helianthus deserticola) have originated independently from the same two parents, Helianthus annuus and Helianthus petiolaris. These hybrid species have different geographical and temporal origins, and two species appear to have multiple origins [52][53][54]. All five species are diploid (2n ¼ 34), self-incompatible and native to central and western North America (figure 1).…”

Section: Introductionmentioning

confidence: 99%

Genomics of homoploid hybrid speciation: diversity and transcriptional activity of long terminal repeat retrotransposons in hybrid sunflowers

Renaut

Rowe

Ungerer

et al. 2014

Phil. Trans. R. Soc. B

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Hybridization is thought to play an important role in plant evolution by introducing novel genetic combinations and promoting genome restructuring. However, surprisingly little is known about the impact of hybridization on transposable element (TE) proliferation and the genomic response to TE activity. In this paper, we first review the mechanisms by which homoploid hybrid species may arise in nature. We then present hybrid sunflowers as a case study to examine transcriptional activity of long terminal repeat retrotransposons in the annual sunflowers Helianthus annuus , Helianthus petiolaris and their homoploid hybrid derivatives ( H. paradoxus , H. anomalus and H. deserticola ) using high-throughput transcriptome sequencing technologies (RNAseq). Sampling homoploid hybrid sunflower taxa revealed abundant variation in TE transcript accumulation. In addition, genetic diversity for several candidate genes hypothesized to regulate TE activity was characterized. Specifically, we highlight one candidate chromatin remodelling factor gene with a direct role in repressing TE activity in a hybrid species. This paper shows that TE amplification in hybrid lineages is more idiosyncratic than previously believed and provides a first step towards identifying the mechanisms responsible for regulating and repressing TE expansions.

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Habitat divergence between a homoploid hybrid sunflower species,Helianthus paradoxus(Asteraceae), and its progenitors

Cited by 82 publications

References 38 publications

Chromosomal Evolution and Patterns of Introgression inHelianthus

Chromosomal Evolution and Patterns of Introgression inHelianthus

The genetic architecture necessary for transgressive segregation is common in both natural and domesticated populations

Genomics of homoploid hybrid speciation: diversity and transcriptional activity of long terminal repeat retrotransposons in hybrid sunflowers

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