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;
Am J Bot. 2008 Dec;95(12):1606-20. doi: 10.3732/ajb.0800148.
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.
异源多倍体形成可能是植物同域物种形成的主要模式。北美有 6 种泥炭藓属植物，其中 3 种为单倍体配子体，3 种被认为是二倍体配子体。微卫星分析表明，某些水藓和皱叶藓的植株在大多数位点都是杂合的，但其他植株在每个位点只有一个等位基因。流式细胞术和 Feulgen 染色显示，杂合植株的基因组大小是每个位点有一个等位基因的植株的两倍；因此，微卫星图谱可用于调查单倍体和二倍体配子体的分布和丰度。微卫星分析还表明，卡罗来纳藓一直是二倍体，但皱叶藓和水藓既包含单倍体也包含二倍体种群。皱叶藓二倍体植株的频率随纬度增加而增加。在对皱叶藓一个种群的分析中，两种倍性同时存在，但遗传分化，没有杂交的证据。遗传分化程度表明，这些二倍体不是由当地单倍体的简单基因组加倍形成的。杂合性似乎在二倍体中是固定的或几乎是固定的，这强烈表明，尽管它们在形态上与单倍体无法区分，但它们是由异源多倍体形成的。
