EAWAG, Swiss Federal Institute of Aquatic Science and Technology, Department of Aquatic Ecology, Uberlandstrasse 133, CH-8600 Dübendorf, Switzerland.
Evolution. 2010 Apr 1;64(4):986-97. doi: 10.1111/j.1558-5646.2009.00872.x. Epub 2009 Oct 23.
Transitions from sexual to asexual reproduction are often coupled with elevations in ploidy. As a consequence, the importance of ploidy per se for the maintenance and spread of asexual populations is unclear. To examine the effects of ploidy and asexual reproduction as independent determinants of the success of asexual lineages, we sampled diploid sexual, diploid asexual, and triploid asexual Eucypris virens ostracods across a European wide range. Applying nuclear and mitochondrial markers, we found that E. virens consists of genetically highly differentiated diploid sexual populations, to the extent that these sexual clades could be considered as cryptic species. All sexual populations were found in southern Europe and North Africa and we found that both diploid asexual and triploid asexual lineages have originated multiple times from several sexual lineages. Therefore, the asexual lineages show a wide variety of genetic backgrounds and very strong population genetic structure across the wide geographic range. Finally, we found that triploid, but not diploid, asexual clones dominate habitats in northern Europe. The limited distribution of diploid asexual lineages, despite their shared ancestry with triploid asexual lineages, strongly suggests that the wider geographic distribution of triploids is due to elevated ploidy rather than to asexuality.
性繁殖向无性繁殖的转变通常伴随着倍性的升高。因此，倍性本身对无性种群的维持和扩散的重要性尚不清楚。为了研究倍性和无性繁殖作为无性谱系成功的独立决定因素的影响，我们在整个欧洲范围内对二倍体有性、二倍体无性和三倍体无性的 Eucypris virens 介形虫进行了采样。应用核和线粒体标记，我们发现 E. virens 由遗传上高度分化的二倍体有性种群组成，这些有性类群可以被视为隐种。所有的有性种群都在欧洲南部和北非发现，我们发现，二倍体无性和三倍体无性谱系都多次从几个有性谱系起源。因此，无性谱系在广泛的地理范围内表现出广泛的遗传背景和非常强的种群遗传结构。最后，我们发现三倍体，而不是二倍体，无性克隆在北欧的栖息地占主导地位。尽管二倍体无性谱系与三倍体无性谱系具有共同的祖先，但它们的分布范围有限，这强烈表明三倍体更广泛的地理分布是由于倍性的升高，而不是无性繁殖。
