Department of Ecology and Evolution, University of Lausanne, Lausanne, Switzerland.
School of Natural Sciences, Bangor University, Bangor, UK.
Proc Biol Sci. 2023 Sep 27;290(2007):20230404. doi: 10.1098/rspb.2023.0404. Epub 2023 Sep 20.
Obligately parthenogenetic species are expected to be short lived since the lack of sex and recombination should translate into a slower adaptation rate and increased accumulation of deleterious alleles. Some, however, are thought to have been reproducing without males for millions of years. It is not clear how these old parthenogens can escape the predicted long-term costs of parthenogenesis, but an obvious explanation is cryptic sex. In this study, we screen for signatures of cryptic sex in eight populations of four parthenogenetic species of stick insects, some estimated to be older than 1 Myr. Low genotype diversity, homozygosity of individuals and high linkage disequilibrium (LD) unaffected by marker distances support exclusively parthenogenetic reproduction in six populations. However, in two populations (namely, of the species and ) we find strong evidence for cryptic sex, most likely mediated by rare males. These populations had comparatively high genotype diversities, lower LD, and a clear LD decay with genetic distance. Rare sex in species that are otherwise largely parthenogenetic could help explain the unusual success of parthenogenesis in the genus and raises the question whether episodes of rare sex are in fact the simplest explanation for the persistence of many old parthenogens in nature.
专性孤雌生殖的物种预计寿命较短，因为缺乏性和重组应该会导致适应速度较慢，有害等位基因的积累增加。然而，有些物种被认为已经在没有雄性的情况下繁殖了数百万年。目前还不清楚这些古老的孤雌生殖生物如何逃避孤雌生殖所预测的长期成本，但一个明显的解释是隐性性别。在这项研究中，我们在 8 个 4 种竹节虫的孤雌生殖物种的种群中筛选隐性性别特征，其中一些估计已有 100 万年以上的历史。低基因型多样性、个体的纯合性和不受标记距离影响的高连锁不平衡 (LD) 支持 6 个种群中仅存在孤雌生殖繁殖。然而，在两个种群（即 和 ）中，我们发现了隐性性别存在的有力证据，很可能是由罕见的雄性介导的。这些种群的基因型多样性相对较高，LD 较低，且随着遗传距离的增加，LD 迅速衰减。在基本上完全是孤雌生殖的物种中出现罕见的雄性，这可能有助于解释 属中孤雌生殖的不寻常成功，并提出了这样一个问题，即罕见的雄性是否实际上是许多古老的孤雌生殖生物在自然界中得以持续存在的最简单解释。
