Is There More Than One Way for Animals to be Anciently Asexual: The Case of the Nothroid Oribatid Mites

大多数动物是有性繁殖的。无性繁殖的物种比例相对较小，通常来自最近的有性物种，即它们是进化的死胡同。这一规则有极少数明显的例外，即整个进化群体都由无性物种组成。其中之一就是诺氏甲螨，这是一组自由生活的土壤螨类，从恐龙之前就已经存在了。将对卵子形成的机制进行详细的研究，以检验一种假说，即一只母螨如何无性繁殖出不会在其DNA中积累有害突变的后代，这是典型无性物种的最终命运。还将寻找在卵细胞生产过程中专门参与DNA修复的基因。如果这些基因存在并活跃，它们可能会减少遗传给后代的突变数量。理解负责有性繁殖起源和维持的进化力量仍然是生物学上的一大挑战。大量的理论和观察都表明，无性物种不可能在长时间的进化过程中生存和多样化。对这一概括的任何例外都很可能是关于是什么因素或因素的组合使有性繁殖保持了生命中几乎无处不在的特征。

Most animals reproduce sexually. The relatively small proportion of species that reproduce without sex generally are derived from recent sexual species, i.e., they are evolutionary dead ends. There are a very few apparent exceptions to this rule, in which entire evolutionary groups are composed of asexual species. One such is the nothroid oribatid mites, a group of free-living soil mites that have been around since before the dinosaurs. Detailed investigations will be made into the mechanisms of egg formation to test a hypothesis on how a mother mite could asexually produce offspring that do not accumulate deleterious mutations in their DNA, the ultimate fate of typical asexual species. Genes involved specifically in DNA repair during the production of egg cells will also be sought. If these genes are present and active, they could be responsible for reducing the number of mutations passed on to offspring.Understanding the evolutionary forces responsible for the origin and maintenance of sexual reproduction remains a major challenge in biology. Large bodies of both theory and observation suggest asexual species cannot survive and diversify over long evolutionary time spans. Any exceptions to this generalization are likely to be very informative about what factor or combination of factors keeps sexual reproduction the nearly ubiquitous feature of life that it is.