Is there hybridization between diploid and tetraploid Euphrasia in a secondary contact zone?

Mr, Brown; Becher, Hannes; Williams, Sebastian; Twyford, Alex D.

doi:10.1002/ajb2.16100

Cited by 4 publications

(1 citation statement)

References 59 publications

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“…Natural hybridization events between diploid and tetraploid species are generally phenomena rarely confirmed in nature, as contrasting ploidy levels represent a known, highly effective barrier to hybridization (Brown et al, 2023;Husband & Sabara, 2004;Koutecký et al, 2011). Abnormal endosperm ratios of maternal to paternal genomes at fertilization prevent hybrid seed formation and later hybrid sterility, leading to aneuploid gametes.…”

Section: Introductionmentioning

confidence: 99%

Limited gene flow in adjacent valleys and genetic introgression in a mountain hybrid zone between Aconitum (Ranunculaceae) species

Mitka,

Boroń,

Warzecha

et al. 2023

Acta Soc Bot Pol

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The number of polyploid plants in angiosperms is estimated at about 30-80%, depending on the study, but hybridization between diploids and tetraploids is not a common phenomenon. In this study, our aim was to determine the extent of hybridization and introgression between Aconitum species in a mountainous hybrid zone in the Tatra Mountains (Western Carpathians). We hypothesized that topography would affect their populations’ genetic structure. For this purpose, inter simple sequence repeat (ISSR) molecular markers and chloroplast DNA (cpDNA, region trnL(UAG)–ndhF) sequencing were used. The results revealed that diploid and tetraploid Aconitum species had specific cpDNA haplotypes, while the spontaneous hybrid species harbored a cpDNA haplotype typical for tetraploids. Bayesian STRUCTURE analysis showed that introgression occurred between diploid and tetraploid species above the tree line, where a spontaneous hybrid, a putative triploid A. ×berdaui, originated, probably via the triploid bridge mechanism. Molecular analysis of variance, principal coordinate analysis, and neighbor-net clustering revealed different genetic profiles of the diploids between neighboring mountain valleys. Hence, mountain topography, ridges, and valleys can form an effective geographical barrier, preventing gene flow over longer distances. Introgression happens near or above the tree line, where the hybridization zone is formed. In the introgressants, however, no morphological alterations were discernible.

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Section: Introductionmentioning

confidence: 99%

Limited gene flow in adjacent valleys and genetic introgression in a mountain hybrid zone between Aconitum (Ranunculaceae) species

Mitka,

Boroń,

Warzecha

et al. 2023

Acta Soc Bot Pol

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Is there hybridization between diploid and tetraploid Euphrasia in a secondary contact zone?

Becher

Williams

et al. 2022

American J of Botany

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Premise: Strong postzygotic reproductive isolating barriers are usually expected to limit the extent of natural hybridization between species with contrasting ploidy. However, genomic sequencing has revealed previously overlooked examples of natural cross-ploidy hybridization in some flowering plant genera, suggesting that the phenomenon may be more common than once thought. We investigated potential cross-ploidy hybridization in British eyebrights (Euphrasia, Orobanchaceae), a group from which 13 putative cross-ploidy hybrid combinations have been reported based on morphology. Methods: We analyzed a contact zone between diploid Euphrasia rostkoviana and tetraploid E. arctica in Wales. We sequenced part of the internal transcribed spacer (ITS) of nuclear ribosomal DNA and used genotyping by sequencing (GBS) to look for evidence of cross-ploidy hybridization and introgression. Results: Common variant sites in the ITS region were fixed between diploids and tetraploids, indicating a strong barrier to hybridization. Clustering analyses of 356 single-nucleotide polymorphisms (SNPs) generated using GBS clearly separated samples by ploidy and revealed strong genetic structure (F ST = 0.44). However, the F ST distribution across all SNPs was bimodal, indicating potential differential selection on loci between diploids and tetraploids. Demographic inference suggested potential gene flow, limited to around one or fewer migrants per generation. Conclusions: Our results suggest that recent cross-ploidy hybridization is rare or absent in a site of secondary contact in Euphrasia. While a strong ploidy barrier prevents hybridization over ecological timescales, such hybrids may form in stable populations over evolutionary timescales, potentially allowing cross-ploidy introgression to take place.

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The puzzle of plant hybridisation: a high propensity to hybridise but few hybrid zones reported

Nieto Feliner,

Criado Ruiz,

Álvarez

et al. 2023

Heredity

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An interesting conundrum was recently revealed by R. Abbott when he found that the number of hybrid zones reported in the literature for plants is very low, given the propensity of plants to hybridise. In another literature survey on hybrid zones performed over the period 1970–2022, we found that the number of hybrid zones reported for vertebrates was 2.3 times greater than that reported for vascular plants, even though there are about six times more vascular plant species than vertebrates. Looking at the number of papers reporting hybrid zones, there are 4.9 times more on vertebrates than on vascular plants. These figures support the relevance of this conundrum. In this paper we aim to shed light on this question by providing a structured discussion of the causes that may underlie this conundrum. We propose six non-mutually exclusive factors, namely lack or deficit of spatial structure, lack or deficit of genetic structure, effects of hybridisation between non-closely related species, lability of plant hybrid zones over time, botanists’ perception of hybridisation, and deficit of population genetic data. There does not appear to be a single factor that explains our puzzle, which applies to all cases of plants where hybridisation is detected but no hybrid zone is reported. It is argued that some plant features suggest that the puzzle is not, at least entirely, due to insufficient knowledge of the specific cases, a hypothesis that should be addressed with a wider range of empirical data across different taxonomic groups.

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Is there hybridization between diploid and tetraploid Euphrasia in a secondary contact zone?

Cited by 4 publications

References 59 publications

Limited gene flow in adjacent valleys and genetic introgression in a mountain hybrid zone between <i>Aconitum</i> (Ranunculaceae) species

Limited gene flow in adjacent valleys and genetic introgression in a mountain hybrid zone between <i>Aconitum</i> (Ranunculaceae) species

Is there hybridization between diploid and tetraploid Euphrasia in a secondary contact zone?

The puzzle of plant hybridisation: a high propensity to hybridise but few hybrid zones reported

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