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

大多数动物有性繁殖。相对较小比例的无性繁殖物种通常是从最近的有性繁殖物种衍生而来的，也就是说，它们是进化的死胡同。对于这一规律，很少有明显的例外，因为整个进化群体都是由无性繁殖的物种组成的。其中一种是nothroid oribatid螨虫，这是一群自由生活的土壤螨虫，在恐龙出现之前就已经存在了。研究人员将对卵的形成机制进行详细的研究，以验证一种假设，即母螨如何能够无性繁殖出不会在DNA中积累有害突变的后代，这是典型无性物种的最终命运。在卵细胞产生过程中，与DNA修复相关的基因也将被寻找。如果这些基因存在并且活跃，它们可能负责减少传递给后代的突变数量。理解导致有性生殖起源和维持的进化力量仍然是生物学中的一个重大挑战。大量的理论和观察都表明，无性物种无法在漫长的进化时间跨度中生存和多样化。这一概括的任何例外都可能提供非常有用的信息，说明是什么因素或因素的组合使有性生殖成为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.