Polyploids with odd-ploidy levels may play an important evolutionary role as they enable backcrosses with their parental cytotypes. We chose the ploidy-variable Senecio carniolicus species group to address the overarching question if pentaploid individuals, which occur at high frequencies in immediate contact zones of parental tetraploids and hexaploids, mediate effective interploidy gene flow. We employed a set of approaches including relative genome size (RGS) determination and viability tests of pollen, RGS of the embryo, viability tests and germination experiments of seeds, and RGS and survival experiments of seedlings to tackle the following specific questions. Is pollen of pentaploid individuals viable suggesting regular meiosis in spite of the odd-ploidy level? Are the five sets of chromosomes split into 2.5 compliments, or rather into two and three compliments? Do crossings between pentaploid individuals produce viable seeds and seedlings, suggesting that pentaploids are an independent evolutionary unit? We found that pollen stainability is not strongly reduced in pentaploids and that the five chromosome complements are most often split into 2.5 complements. Seeds originating from homoploid crossings of pentaploids show a very low viability whereas backcrosses with tetraploids or hexaploids were more successful. No significant difference in seedling survival was observed among the different crossings but seedlings emerging from 5x5x crosses were significantly smaller than both, seedlings from backcrosses and from homoploid parental crosses. Altogether, our results indicate that pentaploids may play an important evolutionary role as mediators of gene flow but that they rather do not form an independent evolutionary unit.

具有多倍体水平的多倍体可能起重要的进化作用，因为它们使它们的亲本细胞型能够回交。我们选择了倍性可变的千里光肉食动物种组来解决最主要的问题，即在亲本四倍体和六倍体的直接接触区中以高频出现的五倍体个体是否介导有效的倍体间基因流。我们采用了一组方法，包括相对基因组大小（RGS）测定和花粉的活力测试，胚胎的RGS，种子的活力测试和发芽实验，以及RGS和幼苗的存活实验，以解决以下特定问题。五倍体个体的花粉是否存在正常的减数分裂现象，尽管呈奇数倍的水平？这五套染色体是分成2.5个互补词，还是分成两个和三个互补子？五倍体个体之间的杂交会产生可行的种子和幼苗吗？暗示五倍体是一个独立的进化单位？我们发现在五倍体中花粉的可染性并没有强烈降低，并且五个染色体的补体最常被分成2.5个补体。来自五倍体同倍体杂交的种子显示出非常低的生存力，而与四倍体或六倍体的回交更成功。在不同的杂交中，未观察到幼苗存活率的显着差异，但从5个出苗的幼苗x 5 x杂交显着小于回交和同倍体亲本杂交的幼苗。总而言之，我们的结果表明五倍体可能作为基因流的介质发挥重要的进化作用，但它们却不构成独立的进化单位。