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Maintaining their genetic distance: Little evidence for introgression between widely hybridizing species of Geum with contrasting mating systems.

ABSTRACT: Within the plant kingdom, many genera contain sister lineages with contrasting outcrossing and inbreeding mating systems that are known to hybridize. The evolutionary fate of these sister lineages is likely to be influenced by the extent to which they exchange genes. We measured gene flow between outcrossing Geum rivale and selfing Geum urbanum, sister species that hybridize in contemporary populations. We generated and used a draft genome of G. urbanum to develop dd-RAD data scorable in both species. Coalescent analysis of RAD data from allopatric populations indicated that the species diverged 2-3 Mya, and that historical gene flow between them was extremely low (1 migrant every 25 generations). Comparison of genetic divergence between species in sympatry and allopatry, together with an analysis of allele frequencies in potential parental and hybrid populations, provided no evidence of contemporary introgression in sympatric populations. Cluster- and species-specific marker analyses revealed that, apart from four early-generation hybrids, individuals in sympatric populations fell into two genetically distinct groups that corresponded exactly to their morphological species classification with maximum individual admixture estimates of only 1-3%. However, we did observe joint segregation of four putatively introgressed SNPs across two scaffolds in the G. urbanum population that was associated with significant morphological variation, interpreted as tentative evidence for rare, recent interspecific gene flow. Overall, our results indicate that despite the presence of hybrids in contemporary populations, genetic exchange between G. rivale and G. urbanum has been extremely limited throughout their evolutionary history.

SUBMITTER: Jordan CY

PROVIDER: S-EPMC5900869 | biostudies-literature | 2018 Mar

REPOSITORIES: biostudies-literature

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Maintaining their genetic distance: Little evidence for introgression between widely hybridizing species of Geum with contrasting mating systems.

Jordan Crispin Y CY Lohse Konrad K Turner Frances F Thomson Marian M Gharbi Karim K Ennos Richard A RA

Molecular ecology 20171209 5

Within the plant kingdom, many genera contain sister lineages with contrasting outcrossing and inbreeding mating systems that are known to hybridize. The evolutionary fate of these sister lineages is likely to be influenced by the extent to which they exchange genes. We measured gene flow between outcrossing Geum rivale and selfing Geum urbanum, sister species that hybridize in contemporary populations. We generated and used a draft genome of G. urbanum to develop dd-RAD data scorable in both sp ...[more]

PMID: 29134729

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Project description:BACKGROUND:Previous studies on the reproductive biology of ferns showed that mating strategies vary among species, and that polyploid species often show higher capacity for self-fertilization than diploid species. However, the amount of intraspecific variation in mating strategy and selfing capacity has only been assessed for a few species. Yet, such variation may have important consequences during colonization, as the establishment of any selfing genotypes may be favoured after long-distance dispersal (an idea known as Baker's law). RESULTS:We examined intra-and interspecific variation in potential for self-fertilization among four rare fern species, of which two were diploids and two were tetraploids: Asplenium scolopendrium (2n), Asplenium trichomanes subsp. quadrivalens (4n), Polystichum setiferum (2n) and Polystichum aculeatum (4n). Sporophyte production was tested at different levels of inbreeding, by culturing gametophytes in isolation, as well as in paired cultures with a genetically different gametophyte. We tested gametophytes derived from various genetically different sporophytes from populations in a recently planted forest colonized through long-distance dispersal (Kuinderbos, the Netherlands), as well as from older, less disjunct populations.Sporophyte production in isolation was high for Kuinderbos genotypes of all four species. Selfing capacity did not differ significantly between diploids and polyploids, nor between species in general. Rather selfing capacity differed between genotypes within species. Intraspecific variation in mating system was found in all four species. In two species one genotype from the Kuinderbos showed enhanced sporophyte production in paired cultures. For the other species, including a renowned out crosser, selfing capacity was consistently high. CONCLUSIONS:Our results for four different species suggest that intraspecific variation in mating system may be common, at least among temperate calcicole ferns, and that genotypes with high selfing capacity may be present among polyploid as well as diploid ferns. The surprisingly high selfing capacity of all genotypes obtained from the Kuinderbos populations might be due to the isolated position of these populations. These populations may have established through single-spore colonization, which is only possible for genotypes capable of self-fertilization. Our results therewith support the idea that selection for selfing genotypes may occur during long-distance colonization, even in normally outcrossing, diploid ferns.

Dataset Information

Maintaining their genetic distance: Little evidence for introgression between widely hybridizing species of Geum with contrasting mating systems.

Publications

Maintaining their genetic distance: Little evidence for introgression between widely hybridizing species of Geum with contrasting mating systems.

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