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      The relation of meiotic behaviour to hybridity, polyploidy and apomixis in the Ranunculus auricomus complex (Ranunculaceae)

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          Abstract

          Background

          Hybridization and polyploidization are powerful evolutionary factors that are associated with manifold developmental changes in plants such as irregular progression of meiosis and sporogenesis. The emergence of apomixis, which is asexual reproduction via seeds, is supposed to be connected to these factors and was often regarded as an escape from hybrid sterility. However, the functional trigger of apomixis is still unclear. Recently formed di- and polyploid Ranunculus hybrids, as well as their parental species were analysed for their modes of mega- and microsporogenesis by microscopy. Chromosomal configurations during male meiosis were screened for abnormalities. Meiotic and developmental abnormalities were documented qualitatively and collected quantitatively for statistical evaluations.

          Results

          Allopolyploids showed significantly higher frequencies of erroneous microsporogenesis than homoploid hybrid plants. Among diploids, F 2 hybrids had significantly more disturbed meiosis than F 1 hybrids and parental plants. Chromosomal aberrations included laggard chromosomes, chromatin bridges and disoriented spindle activities. Failure of megasporogenesis appeared to be much more frequent in than of microsporogenesis is correlated to apomixis onset.

          Conclusions

          Results suggest diverging selective pressures on female and male sporogenesis, with only minor effects of hybridity on microsporogenesis, but fatal effects on the course of megasporogenesis. Hence, pollen development continues without major alterations, while selection will favour apomixis as alternative to the female meiotic pathway. Relation of investigated errors of megasporogenesis with the observed occurrence of apospory in Ranunculus hybrids identifies disturbed female meiosis as potential elicitor of apomixis in order to rescue these plants from hybrid sterility. Male meiotic disturbance appears to be stronger in neopolyploids than in homoploid hybrids, while disturbances of megasporogenesis were not ploidy-dependent.

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          Most cited references 57

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          The ecological genetics of homoploid hybrid speciation.

          Our understanding of homoploid hybrid speciation has advanced substantially since this mechanism of species formation was codified 50 years ago. Early theory and research focused almost exclusively on the importance of chromosomal rearrangements, but it later became evident that natural selection, specifically ecological selection, might play a major role as well. In light of this recent shift, we present an evaluation of ecology's role in homoploid hybrid speciation, with an emphasis on the genetics underlying ecological components of the speciation process. We briefly review new theoretical developments related to the ecology of homoploid hybrid speciation; propose a set of explicit, testable questions that must be answered to verify the role of ecological selection in homoploid hybrid speciation; discuss published work with reference to these questions; and also report new data supporting the importance of ecological selection in the origin of the homoploid hybrid sunflower species Helianthus deserticola. Overall, theory and empirical evidence gathered to date suggest that ecological selection is a major factor promoting homoploid hybrid speciation, with the strongest evidence coming from genetic studies.
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            Are natural hybrids fit or unfit relative to their parents?

            The process of natural hybridization may produce genotypes that establish new evolutionary lineages. However, many authors have concluded that natural hybridization is of little evolutionary importance because hybrids, in general, are unfit relative to their progenitors. Deciding between these alternative conclusions requires that fitness be measured for hybrid classes and parental species. Recent analyses have found that hybrids are not uniformly unfit, but rather are genotypic classes that possess lower, equivalent or higher levels of fitness relative to their parental taxa. Copyright © 1995. Published by Elsevier Ltd.
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              Asynchronous expression of duplicate genes in angiosperms may cause apomixis, bispory, tetraspory, and polyembryony

               John Carman (1997)
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                Author and article information

                Contributors
                birthe-hilkka.barke@biologie.uni-goettingen.de
                Journal
                BMC Plant Biol
                BMC Plant Biol
                BMC Plant Biology
                BioMed Central (London )
                1471-2229
                17 November 2020
                17 November 2020
                2020
                : 20
                Affiliations
                [1 ]GRID grid.7450.6, ISNI 0000 0001 2364 4210, Department of Systematics, Biodiversity and Evolution of Plants, , Albrecht-von-Haller Institute for Plant Sciences, University of Goettingen, ; Untere Karspuele 2, D-37073 Goettingen, Germany
                [2 ]Present Address: Carl von Ossietzky University, Institute of Biology and Environmental Sciences, Carl von Ossietzky Straße 9-11, D-26129 Oldenburg, Germany
                Article
                2654
                10.1186/s12870-020-02654-3
                7672892
                © The Author(s) 2020

                Open AccessThis article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver ( http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data.

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                © The Author(s) 2020

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