A three-step model for the establishment of polyploid plants

Polyploidy, the result of whole genome duplication, is widespread in plants. Over long timescales, polyploids seem to go extinct more often than diploids. Clear genomic signs of long-term polyploid success exist across plants, but they are comparatively rare within individual lineages. To address the 'polyploid paradox' - early success followed by long-term decline - we propose a three-step framework. The first step is 'Supply', the rate at which new polyploids arise, which can spike in stressful conditions because of elevated formation of gametes with unreduced genomes and relatively weak ecological filtering of the generated polyploids. The second step is 'Bridging', which can occur in one or other of two ways: a short-term route, in which genome duplication increases phenotypic and genetic variation and rarely produces phenotypes that fit the new environment; or a longer-term route, when processes that normally exclude rare cytotypes are weakened and polyploids can persist despite the early costs. The third and last step, 'Consolidation' determines evolutionary outcomes, where some polyploids achieve niche divergence and persist alone or jointly with diploids, while many are removed by long-term costs. As a result, even though polyploids often succeed in the short term, relatively few persist over macroevolutionary timescales. We refer to this sequence as Supply-Bridging-Consolidation (SBC). In this view, polyploid success reflects demographic assembly and ecological opportunity; adaptation usually follows establishment, rather than causing it. The framework yields testable predictions and offers a unified understanding of when polyploids flourish and when they falter, and why only a small fraction is ultimately retained.