Karlin Eric F, Smouse Peter E
Environmental Science, School of Theoretical & Applied Science, Ramapo College, Mahwah, NJ 07430-1680, USA.
Department of Ecology, Evolution, and Natural Resources, School of Environmental & Biological Sciences, Rutgers University, New Brunswick, NJ 08901-8551, USA.
Ann Bot. 2017 Aug 1;120(2):221-231. doi: 10.1093/aob/mcw269.
Allopolyploids exhibit both different levels and different patterns of genetic variation than are typical of diploids. However, scant attention has been given to the partitioning of allelic information and diversity in allopolyploids, particularly that among homeologous monoploid components of the hologenome. Sphagnum × falcatulum is a double allopolyploid peat moss that spans a considerable portion of the Holantarctic. With monoploid genomes from three ancestral species, this organism exhibits a complex evolutionary history involving serial inter-subgeneric allopolyploidizations.
Studying populations from three disjunct regions [South Island (New Zealand); Tierra de Fuego archipelago (Chile, Argentina); Tasmania (Australia)], allelic information for five highly stable microsatellite markers that differed among the three (ancestral) monoploid genomes was examined. Using Shannon information and diversity measures, the holoploid information, as well as the information within and among the three component monoploid genomes, was partitioned into separate components for individuals within and among populations and regions, and those information components were then converted into corresponding diversity measures.
The majority (76 %) of alleles detected across these five markers are most likely to have been captured by hybridization, but the information within each of the three monoploid genomes varied, suggesting a history of recurrent allopolyploidization between ancestral species containing different levels of genetic diversity. Information within individuals, equivalent to the information among monoploid genomes (for this dataset), was relatively stable, and represented 83 % of the grand total information across the Holantarctic, with both inter-regional and inter-population diversification each accounting for about 5 % of the total information.
Sphagnum × falcatulum probably inherited the great majority of its genetic diversity at these markers by reticulation, rather than by subsequent evolutionary radiation. However, some post-hybridization genetic diversification has become fixed in at least one regional population. Methodology allowing statistical analysis of any ploidy level is presented.
异源多倍体呈现出与二倍体不同水平和模式的遗传变异。然而，对于异源多倍体中等位基因信息和多样性的分配，尤其是全基因组中同源单倍体成分之间的分配，关注甚少。泥炭藓杂交种（Sphagnum × falcatulum）是一种双异源多倍体泥炭藓，分布于环南极地区的大片区域。该物种具有来自三个祖先物种的单倍体基因组，展现出涉及连续亚属间异源多倍体化的复杂进化历史。
研究了来自三个不连续区域[新西兰南岛；火地群岛（智利、阿根廷）；塔斯马尼亚（澳大利亚）]的种群，检测了在三个（祖先）单倍体基因组中存在差异的五个高度稳定微卫星标记的等位基因信息。利用香农信息和多样性度量，将全倍体信息以及三个组成单倍体基因组内部和之间的信息，划分为种群内和种群间以及区域内和区域间个体的单独成分，然后将这些信息成分转换为相应的多样性度量。
在这五个标记中检测到的大多数（76%）等位基因很可能是通过杂交获得的，但三个单倍体基因组各自内部的信息有所不同，这表明含有不同遗传多样性水平的祖先物种之间存在反复异源多倍体化的历史。个体内部的信息，等同于单倍体基因组之间的信息（对于该数据集），相对稳定，占环南极地区总信息的83%，区域间和种群间的多样化各自约占总信息的5%。
泥炭藓杂交种（Sphagnum × falcatulum）在这些标记处的遗传多样性很可能大部分是通过网状进化继承而来，而非通过后续的进化辐射。然而，一些杂交后的遗传多样化至少在一个区域种群中已经固定下来。本文介绍了允许对任何倍性水平进行统计分析的方法。
