Department of Biology, Duke University, Durham, NC 27708, USA.
Mol Ecol. 2012 Nov;21(21):5280-98. doi: 10.1111/j.1365-294X.2012.05706.x. Epub 2012 Jul 25.
Polyploidy (whole-genome duplication) has contributed significantly to angiosperm evolution and diversification. To date, it has been found that most polyploids are the result of multiple formation events, which may contribute to genetic diversity and affect interfertility among polyploid lineages of independent origin. A recently discovered allotetraploid derivative of Mimulus guttatus and M. nasutus, Mimulus sookensis, is found throughout the valleys of western Oregon and Vancouver Island. Here, we analyse the patterns of nucleotide diversity at three chloroplast and six nuclear loci in M. guttatus, M. nasutus and M. sookensis, to gain insight into the formation of M. sookensis. By analysing the patterns of genetic variation seen in the diploid progenitors in comparison with the variation seen in M. sookensis, we are able to show that M. sookensis has recurrently formed. We also observed that most M. sookensis individuals are fixed heterozygotes at all of the nuclear loci examined, suggesting that duplicate gene loss is not extensive in M. sookensis. To assess the possibility that hybridization among M. sookensis has contributed to genetic diversity, we conducted crossing experiments within M. sookensis. We found that M. sookensis of independent origin are highly interfertile, suggesting that crossing barriers do not exist within M. sookensis, and that hybridization among M. sookensis may result in new recombinant genotypes. Together, the data suggest that although recurrent origins may be common, they can contribute to genetic diversity without contributing to reproductive isolation among independently arisen polyploid lineages.
多倍体（全基因组加倍）为被子植物的进化和多样化做出了重大贡献。迄今为止，人们发现大多数多倍体是多次形成事件的结果，这可能有助于遗传多样性，并影响独立起源的多倍体谱系之间的可育性。最近发现的一种产于俄勒冈州西部和温哥华岛山谷的拟南芥属双色堇和双色堇的异源四倍体衍生物，即双色堇。在这里，我们分析了三个叶绿体和六个核基因座在双色堇、双色堇和双色堇中的核苷酸多样性模式，以深入了解双色堇的形成。通过分析与双色堇相比在二倍体亲本中看到的遗传变异模式，我们能够表明双色堇经常形成。我们还观察到，在所有检查的核基因座中，大多数双色堇个体都是固定的杂合子，这表明在双色堇中重复基因丢失并不广泛。为了评估双色堇之间杂交可能对遗传多样性的贡献，我们在双色堇内进行了杂交实验。我们发现，独立起源的双色堇高度可育，这表明双色堇内不存在杂交障碍，双色堇之间的杂交可能导致新的重组基因型。总之，数据表明，尽管反复出现的起源可能很常见，但它们可以在不导致独立起源的多倍体谱系之间生殖隔离的情况下增加遗传多样性。
