Abstract
AbstractTaxonomists have proposed numerous hybrid species in plants, but to gain a better understanding of the role that hybridization may play in plant diversification, such taxonomic hypotheses must be tested using genomic data. In this study, we employ ddRAD sequence data to test taxonomic hypotheses of hybrid origins in Carex salina and C. ramenskii (Carex section Phacocystis). Sequence data from multiple Norwegian and Icelandic populations of the putative hybrid and parental species were generated for hundreds of ddRAD loci. These data were used to estimate geographical structuring of genetic diversity and admixture and to explicitly test for hybrid origins using several analytical approaches. Our results indicate recurrent hybrid origins for the populations of C. salina and C. ramenskii sampled in our study and show that these populations are characterized by high interspecific heterozygosity. Our results support the idea that hybridization may indeed play an important role in the diversification of lineages of Carex and highlight the important role that clonal propagation might play in maintaining hybrid populations. Future studies focusing on a broader geographical sampling would be needed to assess if the genetic structuring in these Nordic populations reflects range-wide patterns in these hybrid lineages.
Highlights
The formation of hybrids resulting from reproduction between two species is a relatively common phenomenon in plants (Stebbins, 1950; Abbott, Barton & Good, 2016), and estimates of the frequency of interspecific hybridization suggest that 25% or more of all plant species routinely produce hybrid offspring with other species of varying degrees of relatedness (Rieseberg, Wood & Baack, 2006; Mallet, 2005, 2007)
Our results consistently support a scenario in which both C. salina and C. ramenskii originated through interspecific hybridization
In accordance with previous taxonomic hypotheses (Cayouette & Morriset, 1985, 1986; Standley et al, 2002; Kristinsson, 2010; Elven et al, 2011), our results indicate that Norwegian C. salina probably originated through hybridization between C. paleacea and C. subspathacea, and Icelandic C. ramenskii probably originated through hybridization between C. lyngbyei and C. subspathacea
Summary
The formation of hybrids resulting from reproduction between two species is a relatively common phenomenon in plants (Stebbins, 1950; Abbott, Barton & Good, 2016), and estimates of the frequency of interspecific hybridization suggest that 25% or more of all plant species routinely produce hybrid offspring with other species of varying degrees of relatedness (Rieseberg, Wood & Baack, 2006; Mallet, 2005, 2007). Despite the relatively high rate of interspecific hybridization, there is considerable debate regarding the evolutionary importance of this phenomenon because the ultimate outcomes of hybridization are known to vary considerably (Abbott et al, 2013). A third possible outcome of interspecific hybridization is the generation of a new homoploid hybrid species, which is reproductively isolated from the parental species due to ecological niche shifts or the evolution of other pre- or post-zygotic isolating mechanisms (Rieseberg, 1997; Buerkle et al, 2000; Gross & Rieseberg, 2005; Abbott et al, 2010). The earliest stages of homoploid hybrid speciation are most likely to occur in close geographical proximity to one or both of the parental species (i.e. in sympatry; Buerkle et al, 2000), and a newly formed hybrid lineage may be transient if gene flow with parental populations is persistent. Pre- and/or postzygotic reproductive barriers must evolve rapidly for
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