Department of Systematic and Evolutionary Botany, Faculty Centre for Biodiversity, University of Vienna, Rennweg 14, 1030 Vienna, Austria.
Ann Bot. 2010 Mar;105(3):457-70. doi: 10.1093/aob/mcp304. Epub 2010 Jan 24.
Asexual organisms are more widespread in previously glaciated areas than their sexual relatives ('geographical parthenogenesis'). In plants, this pattern is probably dependent on reproductive isolation and stability of cytotypes within their respective distribution areas. Both partial apomixis and introgressive hybridization potentially destabilize the spatial separation of sexual and apomictic populations. The wide distribution of apomicts may be further enhanced by uniparental reproduction which is advantageous for colonization. These factors are studied in the alpine species Ranunculus kuepferi.
Geographical distribution, diversity and mode of reproduction of cytotypes were assessed using flow cytometry and flow cytometric seed screening on samples from 59 natural populations of Ranunculus kuepferi. Seed set of cytotypes was compared in the wild.
Diploid sexuals are confined to the south-western parts of the Alps, while tetraploid apomicts dominate in previously glaciated and in geographically isolated areas despite a significantly lower fertility. Other cytotypes (3x, 5x and 6x) occur mainly in the sympatric zone, but without establishing populations. The tetraploids are predominantly apomictic, but also show a partial apomixis via an uncoupling of apomeiosis and parthenogenesis in the seed material. Both pseudogamy and autonomous endosperm formation are observed which may enhance uniparental reproduction.
Diploids occupy a glacial relic area and resist introgression of apomixis, probably because of a significantly higher seed set. Among the polyploids, only apomictic tetraploids form stable populations; the other cytotypes arising from partial apomixis fail to establish, probably because of minority cytotype disadvantages. Tetraploid apomicts colonize previously devastated and also distant areas via long-distance dispersal, confirming Baker's law of an advantage of uniparental reproduction. It is concluded that stability of cytotypes and of modes of reproduction are important factors for establishing a pattern of geographical parthenogenesis.
无融合生殖生物比其有性亲属（“地理孤雌生殖”）更广泛地分布在以前被冰川覆盖的地区。在植物中，这种模式可能依赖于生殖隔离和其各自分布区内细胞型的稳定性。部分无融合生殖和渐渗杂交都可能破坏有性和无融合生殖群体的空间分离。无融合生殖的广泛分布可能会进一步增强，因为单亲繁殖有利于殖民化。这些因素在高山物种毛茛属 Ranunculus kuepferi 中得到了研究。
使用流式细胞术和流式细胞仪种子筛选对来自 Ranunculus kuepferi 的 59 个自然种群的样本评估细胞型的地理分布、多样性和繁殖方式。在野外比较了细胞型的种子产量。
二倍体有性生殖仅限于阿尔卑斯山的西南部，而四倍体无融合生殖在以前的冰川地区和地理隔离地区占主导地位，尽管其生育力明显较低。其他细胞型（3x、5x 和 6x）主要出现在同域区，但没有建立种群。四倍体主要是无融合生殖的，但在种子材料中也表现出部分无融合生殖，即孤雌生殖和有性生殖的解偶联。观察到假配子和自主胚乳形成，这可能增强单亲繁殖。
二倍体占据了一个冰川遗迹区，并且抵制无融合生殖的渐渗，这可能是因为其种子产量明显更高。在多倍体中，只有无融合生殖的四倍体形成稳定的种群；来自部分无融合生殖的其他细胞型未能建立，这可能是由于少数细胞型的劣势。四倍体无融合生殖通过长距离扩散殖民以前被破坏的和遥远的地区，证实了贝克法则单亲繁殖的优势。综上所述，细胞型的稳定性和繁殖方式是建立地理孤雌生殖模式的重要因素。
