Department of Biology, Texas State University, San Marcos, TX 78666, USA.
Proc Natl Acad Sci U S A. 2013 Aug 20;110(34):13797-802. doi: 10.1073/pnas.1303730110. Epub 2013 Aug 5.
Unisexual sperm-dependent vertebrates are of hybrid origins, rare, and predicted to be short-lived as a result of several challenges arising from their mode of reproduction. In particular, because of a lack of recombination, clonal species are predicted to have a low potential to respond to natural selection. However, many unisexual sperm-dependent species persist, and assessing the genetic diversity present in these species is fundamental to understanding how they avoid extinction. We used population genomic methods to assess genotypic variation within the unisexual fish Poecilia formosa. Measures of admixture and population differentiation, as well as clustering analyses, indicate that the genomes of individuals of P. formosa are admixed and intermediate between Poecilia latipinna and Poecilia mexicana, consistent with the hypothesis of their hybrid origins. Bayesian genomic cline analyses indicate that about 12% of sampled loci exhibit patterns consistent with inheritance from only one parent. The estimation of observed heterozygosity clearly suggests that P. formosa is not comprised of direct descendants of a single nonrecombining asexual F1 hybrid individual. Additionally, the estimation of observed heterozygosity provides support for the hypothesis that the history of this unisexual species has included backcrossing with the parent species before the onset of gynogenesis. We also document high levels of variation among asexual individuals, which is attributable to recombination (historical or ongoing) and the accumulation of mutations. The high genetic variation suggests that this unisexual vertebrate has more potential to respond to natural selection than if they were frozen F1 hybrids.
单性精子依赖的脊椎动物是杂种起源的，它们数量稀少，由于其繁殖方式带来的多种挑战，预计寿命较短。特别是，由于缺乏重组，克隆物种预计对自然选择的适应能力较低。然而，许多单性精子依赖的物种仍然存在，评估这些物种的遗传多样性对于理解它们如何避免灭绝至关重要。我们使用群体基因组学方法评估了单性精子依赖的鱼类 Poecilia formosa 内的基因型变异。杂种和种群分化的衡量标准以及聚类分析表明，P. formosa 个体的基因组是混合的，介于 Poecilia latipinna 和 Poecilia mexicana 之间，这与它们的杂种起源假说一致。贝叶斯基因组渐变分析表明，约 12%的采样基因座表现出仅来自一个亲本的遗传模式。观察到的杂合度的估计清楚地表明，P. formosa 不是由单一非重组无性 F1 杂种个体的直系后代组成的。此外，观察到的杂合度的估计为这个单性物种的历史包括在雌核发育发生之前与亲代物种的回交假说提供了支持。我们还记录了无性个体之间存在高水平的变异，这归因于重组（历史上或正在进行的）和突变的积累。高遗传变异表明，与被冻结的 F1 杂种相比，这种单性脊椎动物对自然选择的适应能力更强。
