Department of Biogeography and Botanical Garden, University of Vienna, Rennweg 14, Vienna 1030, Austria.
Ann Bot. 2010 Dec;106(6):967-77. doi: 10.1093/aob/mcq192. Epub 2010 Sep 29.
The spatial distribution of cytotypes can provide valuable insights into evolutionary patterns of polyploid complexes. In a previous study the macro-scale distribution of the three main cytotypes in Senecio carniolicus (Asteraceae) within the Eastern Alps was characterized. Employing a roughly 12-fold extended sampling, the present study focuses on unravelling patterns of cytotype distribution on the meso- and microscale and on correlating those with ecological properties of the growing sites.
DAPI flow cytometry of dried samples was used to determine DNA ploidy level in 5033 individuals from 100 populations spread over the entire Eastern Alpine distribution area of S. carniolicus. Descriptors of microhabitats as well as spatial data were recorded in the field, and analysed with a mixed-effects ANOVA.
Extensive variation in DNA ploidy levels (2x, 3x, 4x, 5x, 6x, 7x, 8x, 9x) was detected. Of the main cytotypes, diploids and hexaploids were widespread and had strongly overlapping distributions resulting in the frequent occurrence of cytotype mixtures (half of the investigated populations), whereas tetraploids were disjunctly distributed and occurred in the south-west and the east of the species' distribution area. In spite of the frequent co-occurrence of cytotypes, only 1 % of the samples belonged to secondary cytotypes (3x, 5x, 7x, 8x, 9x). Diploids, tetraploids and hexaploids were altitudinally segregated, but with broad overlap. Similarly, highly significant differences in vegetation and rock cover as well as microhabitat exposure were found between the main cytotypes.
Senecio carniolicus shows a remarkable diversity of cytotypes. The distribution of the three main cytotypes (2x, 4x, 6x) has been shaped by Pleistocene glaciations to different extents. Whereas tetraploids are nearly entirely restricted to refugia, hexaploids colonized areas that were extensively glaciated. Diploid and hexaploid individuals often co-occur in mixed populations, where they are spatially and ecologically segregated at both the meso-scale (altitudinal differentiation, exposure of the growing site) and the micro-scale (cover of vegetation and bare rock). With regard to the ecological parameters investigated, the tetraploid cytotype occupies an intermediate position. The rareness of secondary cytotypes suggests the presence of strong pre- or post-zygotic mating barriers.
细胞型的空间分布可以为多倍体复合体的进化模式提供有价值的见解。在之前的研究中，对东部阿尔卑斯山的千里光（菊科）三种主要细胞型的宏观尺度分布进行了描述。本研究采用大约 12 倍的扩展采样，重点揭示细胞型在中尺度和微尺度上的分布模式，并将这些模式与生长地点的生态特性相关联。
对来自千里光整个东部阿尔卑斯山分布区的 100 个种群的 5033 个个体的干燥样本进行 DAPI 流式细胞术，以确定 DNA 倍性水平。在野外记录微生境描述符和空间数据，并进行混合效应方差分析。
检测到广泛的 DNA 倍性水平（2x、3x、4x、5x、6x、7x、8x、9x）变化。在主要细胞型中，二倍体和六倍体分布广泛，分布重叠强烈，导致细胞型混合物频繁发生（一半的研究种群），而四倍体则呈离散分布，分布在物种分布区的西南部和东部。尽管细胞型经常共存，但只有 1%的样本属于次生细胞型（3x、5x、7x、8x、9x）。二倍体、四倍体和六倍体在海拔上是分开的，但有很大的重叠。同样，在主要细胞型之间也发现了植被和岩石覆盖率以及微生境暴露的高度显著差异。
千里光表现出显著的细胞型多样性。三种主要细胞型（2x、4x、6x）的分布受到更新世冰川作用的不同程度影响。四倍体几乎完全局限于避难所，而六倍体则在广泛受冰川作用影响的地区进行了殖民。二倍体和六倍体个体经常在混合种群中共存，在中尺度（海拔分化、生长地点的暴露）和微尺度（植被和裸岩覆盖）上存在空间和生态分离。就所研究的生态参数而言，四倍体细胞型占据中间位置。次生细胞型的罕见表明存在强烈的合子前或合子后交配障碍。
