Diploid and autotetraploid sexuals and their relationships to apomicts in the Ranunculus cassubicus group:: insights from DNA content and isozyme variation
Diploid and autotetraploid sexuals and their relationships to apomicts in the Ranunculus cassubicus group:: insights from DNA content and isozyme variation
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DOI：
10.1007/s00606-002-0209-x
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发表时间：
2002-01-01
影响因子：
1.9
通讯作者：
Greilhuber, J
中科院分区：
文献类型：
--
作者：
Hörandl, E;Greilhuber, J
在auricomus复合体的一个亚群——无孢子毛茛（runculus cassubicus）类群中，发现了两个同时具有二倍体和四倍体细胞体的种（R. cassubicifolius W. Koch和R. carpaticola Soo）。对两种植物的9个种群样本进行了倍性水平和同工酶变异分析。DNA图像分析表明，来自巴伐利亚州和萨尔茨堡的3个cassubicicolius居群为二倍体，来自下奥地利州的2个居群为四倍体。来自斯洛伐克中部的两个种群和来自罗马尼亚的一个种群是二倍体，来自斯洛伐克北部的一个种群是六倍体。多倍体群体的c值略小于二倍体群体的c值。倍性水平在种群内是一致的，这与先前的假设相矛盾，即二倍体-四倍体-二单倍体无染色体分裂个体的循环发生在金发姑娘的自然种群中。对9个多态性位点的同工酶-同工酶分析表明，二倍体和四倍体群体的个体变异和遗传测量与有性类群相当。四倍体cassubiciolius的多重等位基因和不平衡的基因剂量证明了其极有可能是多重起源的自倍体。cassubicifolius二倍体居群中纯合子数量的增加和居群间的高度多样性很可能是由于居群的地理隔离造成的，这种隔离可能发生在Wurm冰期，并可能促进了分布范围最东端同源四倍体的分离。利用UPGMA分析了两类群间有性居群的遗传距离值。基于等位基因存在/缺失矩阵的多维尺度个体（包括单聚体）证实了cassubiciciolius和carpaticola之间存在重叠区。六倍体柠条种群表现为基因型多样性降低，杂合子数量增加，杂合子固定，为典型的无融合繁殖模式。该种群具有两种相同的等位基因，但没有特定的等位基因，多维尺度确定了cassubicifolius的基因型。因此，六倍体单性体可能来源于cassubiciciolius和carpaticola的杂交体。一般来说，自多倍体可能促进了cassubicus复合体中无性系的进化，因为它们可以在生殖系统之间提供桥梁，否则就会被倍性水平隔离，也是无融合的自发起源的起点。
From the predominantly aposporous Ranunculus cassubicus group, a subgroup of the R. auricomus complex, two species with both diploid and tetraploid cytodemes (R. cassubicifolius W. Koch and R. carpaticola Soo) were known. Nine population samples of both species have been analyzed for variation of ploidy levels and isozymes. DNA image analysis showed that three populations of R. cassubicifolius from Bavaria and Salzburg are diploid, two from Lower Austria tetraploid. In R. carpaticola, two populations from Central Slovakia and one from Romania are diploid, one from northern Slovakia is hexaploid. The polyploid populations had somewhat smaller C-values than expected from diploids. Ploidy levels are consistent within populations, contradicting previous hypotheses that cycles of diploid-tetraploid-dihaploid apomictic individuals occur in natural populations of goldilocks. Isozyme-allozyme analysis of nine polymorphic loci showed that individual variation and genetic measures of diploid and tetraploid populations are equivalent to those of sexual taxa. Multiple allelism and unbalanced gene dosages in tetraploid R. cassubicifolius give evidence for autopolyploidy that is most probably of multiple origin. The observed excess of homozygotes and the high diversity between populations in the diploid populations of R. cassubicifolius are most probably due to geographical isolation of population groups, that Might have happened during the Wurm glaciation and might have promoted the separation of autotetraploids in the easternmost part of the distribution range. Genetic distance values analyzed by UPGMA of all sexual populations separated the two taxa and the cytodemes within R. cassubicifolius. Multidimensional scaling of individuals (including the apomicts) based on a presence/absence matrix of alleles confirmed this differentiation with an overlapping zone between R. cassubicifolius and R. carpaticola. The hexaploid R. carpaticola population showed reduced genotypic diversity, an increased number of heterozygotes and fixed heterozygosity as typical for apomictic mode of reproduction. This population shared alleles of both species without any specific ones, multidimensional scaling placed genotypes among R. cassubicifolius. Thus, the hexaploid apomicts might have originated from hybrids of R. cassubicifolius and R. carpaticola. In general, evolution of agamic lineages in the R. cassubicus complex might have been facilitated by autopolyploids, because they can provide a bridge between the reproductive systems that are otherwise isolated by ploidy levels, and also a starting point for spontaneous origin of apomixis.