Schön I, Gandolfi A, Di Masso E, Rossi V, Griffiths H I, Martens K, Butlin R K
Department of Biology, University of Leeds, Leeds LS2 9JT, UK.
Heredity (Edinb). 2000 Feb;84 ( Pt 2):161-9. doi: 10.1046/j.1365-2540.2000.00647.x.
The ostracod species Eucypris virens exhibits geographical parthenogenesis, with rare sexual populations in southern Europe and widespread asexual populations elsewhere. DNA sequence data from the nuclear ITS1 and mitochondrial COI regions have been used to estimate genetic variabilities and reconstruct phylogenies. The observed divergence was exceptionally high, with intraspecific maxima of 10.3% (ITS1) and 20.9% (COI) among European lineages, levels reported for interspecific comparisons of other taxa. Phylogenetic reconstructions reveal multiple origins of asexual clones from sexual populations. However, we argue that such data can only provide a lower limit on the number of origins of asexual reproduction, and an upper limit on the age of asexual lineages. Congruence between gene trees for different loci can provide support for the inference of long-term apomictic reproduction. Nuclear and mitochondrial data differ in their placement of some asexual clones, possibly indicating that genetic exchange has taken place between sexual and asexual lineages. Such intraspecific hybridization is one route to combine the benefits of both reproductive modes, and it might explain how asexuality managed to persist in E. virens even in long, evolutionary terms.
介形虫物种绿真星介呈现地理孤雌生殖现象，在欧洲南部有罕见的有性种群，而在其他地方则广泛分布着无性种群。来自核内ITS1和线粒体COI区域的DNA序列数据已被用于估计遗传变异性并重建系统发育。观察到的分歧异常高，欧洲谱系内种内最大值在ITS1区域为10.3%，在COI区域为20.9%，这是其他分类群种间比较所报告的水平。系统发育重建揭示了无性克隆源自多个有性种群。然而，我们认为此类数据只能提供无性繁殖起源数量的下限以及无性谱系年龄的上限。不同基因座的基因树之间的一致性可为长期无融合生殖的推断提供支持。核数据和线粒体数据在一些无性克隆的位置上存在差异，这可能表明有性和无性谱系之间发生了基因交换。这种种内杂交是结合两种生殖方式优势的一条途径，这或许可以解释无性生殖如何能够在绿真星介中持续存在，即便从长期进化角度来看也是如此。
