Pathways to polyploidy: indications of a female triploid bridge in the alpine species Ranunculus kuepferi (Ranunculaceae)

Schinkel, Christoph C. F.; Kirchheimer, Bernhard; Dullinger, Stefan; Geelen, Danny; Storme, Nico De; Hörandl, Elvira

doi:10.1007/s00606-017-1435-6

Cited by 64 publications

(67 citation statements)

References 106 publications

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“…(ii) Following the all-in-one model, autopolyploid derivatives of these can be formally included in these basic species, regardless of whether they remain sexual or shift towards TAXON 67 (6) • December 2018: 1066-1081 Hörandl • Classification of asexual organisms facultative apomixis. These species can include occasional local backcrosses between cytotypes, and/or the triploid individuals (B III hybrids) that occur during a recurrent polyploidization process (Schinkel & al., 2017). Autopolyploid cytotypes may be classified as subspecies if it appears to be useful to recognize ecological or geographical differentiation.…”

Section: From Theory To Practice: Species Delimitationmentioning

confidence: 99%

The classification of asexual organisms: Old myths, new facts, and a novel pluralistic approach

Hörandl

2018

TAXON

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Organisms reproducing via asexuality harbor a great diversity of lineages, morphotypes and ecotypes. However, classification of asexual taxa does not fit into contemporary species concepts, and hence the diversity of apomictic plant complexes is not well reflected in taxonomy. Plants reproducing via apomixis (i.e., asexual seed formation = agamospermy) exemplify the theoretical and practical problems of classification. Obligately asexual organisms do not form reproductive communities, but they do constitute ancestor-descendant lineages. From the conceptual side, evolutionary lineage concepts would fit best for species delimitation. Recent research showed that these lineages are not necessarily threatened by rapid extinction and do have persistence in time and space. Facultative sexuality and low levels of residual recombination counteract the accumulation of deleterious mutations due to the lack of recombination (Muller's ratchet). Apomictic lineages do have adaptive potential, which is demonstrated by the ability to occupy large distribution areas and to experience ecological niche shifts. The challenge for classification of asexual lineages, however, is to find operational criteria for species delimitation. Current practices of species delimitation can be grouped into four main principles: (1) the sexuals-first principle means that obligate sexual progenitor species are classified separately from their apomictic derivatives.(2) The all-in-one principle merges sexual progenitors and highly facultative apomictic derivatives into one species, whereby the apomicts often represent autopolyploids without differentiated phenotypes. (3) The cluster concept applies to allopolyploid complexes with facultative apomixis and a huge diversity of genotypes and morphotypes; here the main genetic clusters are treated as species. (4) Almost obligate apomictic lineages are being classified as agamospecies. The four principles reflect quite well evolutionary traits and diversity of lineages. Finally, a recommendation for a workflow is given, following this gradient from obligate sexuality to obligate apomixis.

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Section: From Theory To Practice: Species Delimitationmentioning

confidence: 99%

The classification of asexual organisms: Old myths, new facts, and a novel pluralistic approach

Hörandl

2018

TAXON

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“…The triploid plant may have arisen as a result of unilateral polyploidization through the fusion of one reduced (x) with one unreduced (2x) gamete (triploid bridge) (De Storme & Mason, 2014). In genetic studies in Ranunculus, unreduced egg cell formation and B III offspring in apomictic plants is an important pathway to polyploidization (female triploid bridge) (Schinkel & al., 2017;Klatt & al., 2018), although our results did not allow us to determine the parental origin of the unreduced gamete. Diploid L. ovalifolium produce reduced and unreduced gametes, which form viable pollen grains with various sizes (Róis & al., 2012).…”

Section: Discussionmentioning

confidence: 99%

Limonium homoploid and heteroploid intra‐ and interspecific crosses unveil seed anomalies and neopolyploidy related to sexual and/or apomictic reproduction

Conceição

Róis

Caperta

2018

TAXON

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Apomixis is a form of asexual reproduction that consists in cloning through seeds. In Limonium (Plumbaginaceae) species present a pollen-stigma dimorphism linked to a sporophytic self-incompatibility system associated with sexual and/ or apomictic reproductive modes. Previous work in other genera suggests that the emergence of apomixis is associated with hybridization and/or polyploidy. In this study, our goal was to test the ability of diploid and tetraploid species to hybridize and to evaluate the variate outcomes from these crosses. To achieve this, sexual diploid (L. nydeggeri, L. ovalifolium) and facultative apomict tetraploid (L. binervosum, L. dodartii) plants from cultivated material, previously cytogenetically and reproductively characterized, were used for experimental intra-and interspecific crosses. Genome sizes, ploidy levels and morphology were examined in the resulting progenies. Results showed a high production of viable seeds in particular in plants from tetraploid × diploid (heteroploid) crosses. In these crosses, some seedlings exhibited pleiocotyly (tricotyl, tetracotyl), while others showed polyembryony. In both homoploid (diploid × diploid) and heteroploid (tetraploid × diploid) crosses, most of the offspring plants were morphologically and in their ploidy similar to the female receiver, although some morphological abnormalities were found. Molecular progeny tests using the nrDNA ITS1-ITS2 sequence demonstrated an astounding range of diploid offspring plants originated from diploid × diploid crosses that were either genetically similar or distinct from parental plants. Although in intraspecific crosses most of the resulting progeny was diploid, one triploid plant was formed. Moreover, in homoploid interspecific crosses, neopolyploids (two tetraploid plants) were produced. Progeny plants from heteroploid crosses always showed nrDNA ITS1-ITS2 sequences identical to the parental plant used as female receiver. In conclusion, diploid homoploid crosses presented genetically diverse offspring arising from sexual reproduction. By contrast, heteroploid crosses generated clonal, maternal (apomictic) offspring. (Tables S1-S3, Fig. S1) and DNA sequence alignments (used to compare parental and progeny plants of nine homoploid and/or interploid crosses) are available from https://doi. Supplementary Material The Electronic Supplement

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“…The frequency of natural emergence of triploid plants has been found to be approximately 0.1% in a population of roughly 55,000 field-grown tomato plants (Rick, 1945) and 0.01-0.29% in 22 varieties of barley (Sandfaer, 1975). These results suggest that triploid plant is key intermediate for the emergence of polyploid individuals, and this TODA AND OKAMOTO | 375 pathway of tetraploid formation is known as a triploid bridge (Comai, 2005;Ramsey & Schemske, 1998;Rieseberg & Willis, 2007;Schinkel et al, 2017).…”

Section: Triploid Plants: Key Intermediates For Polyploidizationmentioning

confidence: 99%

Polyspermy in angiosperms: Its contribution to polyploid formation and speciation

Toda

Okamoto

2019

Molecular Reproduction Devel

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Polyploidization has played a major role in the long‐term diversification and evolutionary success of angiosperms. Triploid formation among diploid plants, which is generally considered to be achieved by fertilization of an unreduced gamete with a reduced one, has been accepted as a means of polyploid production. In addition, it has been supposed that polyspermy also contributes to the triploid formation in maize, wheat, and some orchids; however, such a mechanism has been considered uncommon because reproducing the polyspermic situation and unambiguously investigating developmental profiles of polyspermic zygotes are difficult. To overcome these problems, rice polyspermic zygotes have been successfully produced by electrofusion of an egg cell with two sperm cells, and their developmental profiles have been monitored. The triploid zygotes progress through karyogamy and divide into two‐celled embryos via a typical bipolar mitotic division; the two‐celled embryos further develop into triploid plants, indicating that polyspermic plant zygotes, unlike those of animals, can develop normally. Furthermore, progenies consisting of triparental genetic materials have been successfully obtained in Arabidopsis through the pollination of two different kinds of male parents with a female parent. These different pieces of evidence for development and emergence of polyspermic zygotes in vitro and in planta suggest that polyspermy is a key event in polyploidization and species diversification.

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Pathways to polyploidy: indications of a female triploid bridge in the alpine species Ranunculus kuepferi (Ranunculaceae)

Cited by 64 publications

References 106 publications

The classification of asexual organisms: Old myths, new facts, and a novel pluralistic approach

The classification of asexual organisms: Old myths, new facts, and a novel pluralistic approach

Limonium homoploid and heteroploid intra‐ and interspecific crosses unveil seed anomalies and neopolyploidy related to sexual and/or apomictic reproduction

Polyspermy in angiosperms: Its contribution to polyploid formation and speciation

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