Department of Biological and Environmental Science, University of Jyväskylä, Jyväskylä, Finland.
Heredity (Edinb). 2010 Oct;105(4):341-7. doi: 10.1038/hdy.2010.31. Epub 2010 Apr 7.
Apomictic parthenogens are clonal organisms with limited genetic opportunity for increasing diversity beyond mutation. However, such species can be successful and have been shown to harbor more genetic diversity than might be expected. Here we surveyed diversity of the cytochrome oxidase subunit I gene from the mitochondrial genome of the earthworm Dendrobaena octaedra, an apomictic parthenogen. Diversity estimates made previously from allozyme markers for this species were high, but could have been affected by a detection bias, namely variable expression of alleles in the polyploid genome. We found similarly high mtDNA diversity over three localities in Finland, each represented by two sites; either with or without anthropogenic soil metal contamination. A single haplotype was most common over all sites, and over two thirds of all haplotypes sampled were similar to it in sequence (only varying by 1-3 substitutions). However, more divergent rare haplotypes were also found in one locality, Imatra, in southeast Finland close to the Karelian Isthmus. Metal contamination in the soil did not have a significant effect on genetic diversity, although metal exposure is known to be detrimental to the worms. There was no evidence for cryptic species within D. octaedra and phylogenetic analyses showed some structure of lineages that may have diverged in historical glacial refugia. Other mechanisms, such as rare genetic exchange with closely related species or high mutation and dispersal rates may explain high genetic diversity in D. octaedra.
无融合生殖的孤雌生殖生物是克隆生物，除了突变之外，它们增加多样性的遗传机会有限。然而，这些物种可以取得成功，并且已经证明它们拥有比预期更多的遗传多样性。在这里，我们调查了无融合生殖的孤雌生殖蚯蚓 Octodrilus complanatus 的线粒体基因组细胞色素氧化酶亚基 I 基因的多样性。此前，基于同种异体酶标记对该物种进行的多样性估计值很高，但可能受到检测偏差的影响，即多倍体基因组中等位基因的可变表达。我们在芬兰的三个地点（每个地点都有两个地点）都发现了类似的 mtDNA 多样性，这些地点要么没有受到人为土壤金属污染，要么受到了污染。所有地点最常见的都是单一单倍型，三分之二以上的抽样单倍型与它在序列上相似（仅相差 1-3 个替换）。然而，在芬兰东南部靠近卡累利阿地峡的伊马特拉的一个地点也发现了更多分化的稀有单倍型。土壤中的金属污染对遗传多样性没有显著影响，尽管金属暴露已知对蚯蚓有害。在 Octodrilus complanatus 中没有发现隐种的证据，系统发育分析显示出一些可能在历史冰川避难所中分化的谱系结构。其他机制，例如与密切相关的物种进行罕见的遗传交换或高突变和扩散率，可能解释了 Octodrilus complanatus 中遗传多样性较高的原因。
