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(American Journal of Botany. 2008;95:1606-1620.) doi: 10.3732/ajb.0800148 © 2008 Botanical Society of America, Inc.

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Cytotype variation and allopolyploidy in North American species of the Sphagnum subsecundum complex (Sphagnaceae)¹

² Departamento de Botânica, Faculdade de Ciências da Universidade do Porto, Rua do Campo Alegre 1181, 4150-191 Porto, Portugal and CIBIO, Centro de Investigação em Biodiversidade e Recursos Genéticos, Universidade do Porto, Campus Agrário de Vairão, 4485-661 Vairão, Portugal; ³ Duke University, Department of Biology, Durham, North Carolina 27708 USA ⁴ Molecular and Environmental Plant Sciences Program, Texas A&M University, College Station, Texas 77840 USA ⁵ Department of Systematic and Evolutionary Botany, Faculty of Life Sciences, University of Vienna, Rennweg 14, A 1030 Vienna, Austria ⁶ School of Theoretical & Applied Science, Ramapo College Mahwah, New Jersey 07430 USA

ABSTRACT

Allopolyploid speciation is likely the predominant mode of sympatric speciation in plants. The Sphagnum subsecundum complex includes six species in North America. Three have haploid gametophytes, and three are thought to have diploid gametophytes. Microsatellite analyses indicated that some plants of S. inundatum and S. lescurii are heterozygous at most loci, but others have only one allele at each locus. Flow cytometry and Feulgen staining showed that heterozygous plants have twice the genome size as plants with one allele per locus; thus, microsatellite patterns can be used to survey the distribution and abundance of haploid and diploid gametophytes. Microsatellite analyses also revealed that S. carolinianum is consistently diploid, but S. lescurii and S. inundatum include both haploid and diploid populations. The frequency of diploid plants in S. lescurii increases with latitude. In an analysis of one population of S. lescurii, both cytotypes co-occurred but were genetically differentiated with no evidence of interbreeding. The degree of genetic differentiation showed that the diploids were not derived from simple genome duplication of the local haploids. Heterozygosity appears to be fixed or nearly so in diploids, strongly suggesting that although morphologically indistinguishable from the haploids, they are derived by allopolyploidy.

Key Words: allopolyploidy • cytotypes • Feulgen staining • flow cytometry • microsatellites • polyploidy • Sphagnaceae • Sphagnum

Received for publication 28 June 2008. Accepted for publication 25 August 2008.

FOOTNOTES

¹ This research was supported by FCT grant no. SFRH/BD/21643/2005 to MR and NSF grant no. DEB-0515749 to A.J.S. The authors thank R. Andrus (and BING) for the loan of herbarium specimens.

⁷ Author for correspondence (e-mail: mdf7{at}duke.edu)

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