Is lack of cycad (Cycadales) diversity a result of a lack of polyploidy? |
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Authors: | ROOT GORELICK KRYSTLE OLSON |
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Institution: | 1. Department of Biology, Carleton University, 1125 Colonel By Drive, Ottawa, ON, Canada, K1S 5B6;2. School of Mathematics and Statistics, Carleton University, Ottawa, ON, Canada, K1S 5B6 |
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Abstract: | Many hypotheses exist for the relative diversity of seed plant taxa. We discuss one of them: how the relative dearth of cycad diversity throughout their 300 million year history may be a result of a lack of duplication of their entire nuclear genome, often termed polyploidy. We show theoretically how polyploidy causes speciation via cryptic reproductive isolation. Polyploidy can also cause radiations via epigenetically induced heterochrony and plasticity. Most cycads have only a few large chromosomes because of a lack of whole genome duplication or, except possibly in the genus Zamia, chromosomal fission. Large chromosomes and extremely small effective population sizes result in substantial linkage disequilibrium, genetic hitchhiking and genetic drift in cycads. By contrast, other seed plants have higher incidences of polyploidy and may therefore have been more prone to radiations. © 2011 The Linnean Society of London, Botanical Journal of the Linnean Society, 2011, 165 , 156–167. |
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Keywords: | chromosomal duplication chromosomal fission cytosine methylation epigenetics gymnosperms karyotypic fission paedomorphism radiation seed plants stasis whole genome duplication |
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