The occurrence of triploid hybrids in nature is scarce due to the so-called triploid block representing formation of nonviable progeny after mating diploid with tetraploid. Here we describe frequent presence of triploids originating from hybridization of diploid Festuca pratensis with tetraploid F. apennina in the Swiss Alps. F. pratensis is a forage grass grown in lowlands and up to 1800 m a.s.l., while F. apennina is a mountain grass found in elevations from 1100 to 2000 m a.s.l. In the overlapping zone these species often grow sympatrically and triploid hybrids have been observed. We show that elevation is the main factor in the distribution of plants with various ploidy levels. Diploids occupy lower elevations, while triploids predominate in the mid-elevation zones and tetraploids are the most frequent in higher elevations. Other factors, such as topography and soil composition probably have only marginal effects on the distribution of the plants with different ploidy levels. Triploids seem to be frequently formed in the Swiss Alps and crosses in both directions are involved in the formation of triploid hybrids. As shown by chloroplast DNA analysis, F. apennina more frequently serves as female. Our analysis suggests that in the mid-elevation zones, triploids have a higher level of competitiveness than both parents. Triploids can overgrow microhabitats to a much higher extent than tetraploids. Such frequent occurrence and local dominance of triploids can at least be partially explained by asexual reproduction. Using DNA markers, we show that triploids can disperse ramets of a single clone over a distance of at least 14.4 m.

中文翻译：

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三倍体杂种Festuca pratensis×F. apennina在瑞士阿尔卑斯山频繁发生

由于所谓的三倍体块代表二倍体与四倍体交配后无生命的后代的形成，自然界中三倍体杂种的发生很少。在这里，我们描述了三倍体在二倍体Festuca pratensis与四倍体F. apennina在瑞士阿尔卑斯山杂交中的频繁存在。F. pratensis是生长在低地并高达1800 m asl的牧草，而F. apennina是在海拔1100至2000 m处发现的高山草。在重叠区，这些物种经常同胞生长，并且观察到三倍体杂种。我们表明，海拔高度是不同倍性水平植物分布的主要因素。二倍体的海拔较低，而三倍体的海拔较高，而四倍体的海拔较高。其他因素，例如地形和土壤组成，可能对不同倍性水平植物的分布只产生边际影响。三倍体似乎在瑞士阿尔卑斯山经常形成，并且双向杂交都参与了三倍体杂种的形成。如叶绿体DNA分析所示，山茱F更频繁地担任女性。我们的分析表明，在高海拔地区，三倍体的竞争性高于父母双方。与四倍体相比，三倍体可以使微栖息地过度生长。三倍体的这种频繁发生和局部优势至少可以通过无性繁殖来部分解释。使用DNA标记，我们显示三倍体可以将单个克隆的分株分散在至少14.4 m的距离上。