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

大多数动物都是有性繁殖。 相对较小比例的无性繁殖物种通常来自最近的有性物种，即，它们是进化的死胡同 这一规律有极少数明显的例外，即整个进化群体都是由无性物种组成的。 其中之一是nothroid甲螨，这是一群在恐龙之前就存在的自由生活的土壤螨。 将对卵形成的机制进行详细的研究，以检验一个假设，即母螨如何无性繁殖后代，而后代的DNA不会积累有害的突变，这是典型的无性繁殖物种的最终命运。 还将寻找在卵细胞产生过程中专门参与DNA修复的基因。 如果这些基因存在并活跃，它们可能负责减少遗传给后代的突变数量。了解负责有性生殖起源和维持的进化力量仍然是生物学的主要挑战。 大量的理论和观察都表明，无性繁殖的物种在漫长的进化过程中无法生存和多样化。 这个概括的任何例外都可能是非常有用的，关于是什么因素或因素的组合使有性生殖成为几乎普遍存在的生命特征。

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.