Howard Hughes Medical Institute and Stowers Institute for Medical Research, Kansas City, MO 64110, USA.
Proc Natl Acad Sci U S A. 2011 Jun 14;108(24):9910-5. doi: 10.1073/pnas.1102811108. Epub 2011 May 4.
Speciation in animals commonly involves an extrinsic barrier to genetic exchange followed by the accumulation of sufficient genetic variation to impede subsequent productive interbreeding. All-female species of whiptail lizards, which originated by interspecific hybridization between sexual progenitors, are an exception to this rule. Here, the arising species instantaneously acquires a novel genotype combining distinctive alleles from two different species, and reproduction by parthenogenesis constitutes an effective intrinsic barrier to genetic exchange. Fertilization of diploid parthenogenetic females by males of sexual species has produced several triploid species, but these instantaneous speciation events have neither been observed in nature nor have they been reconstituted in the laboratory. Here we report the generation of four self-sustaining clonal lineages of a tetraploid species resulting from fertilization of triploid oocytes from a parthenogenetic Aspidoscelis exsanguis with haploid sperm from Aspidoscelis inornata. Molecular and cytological analysis confirmed the genetic identity of the hybrids and revealed that the females retain the capability of parthenogenetic reproduction characteristic of their triploid mothers. The tetraploid females have established self-perpetuating clonal lineages which are now in the third generation. Our results confirm the hypothesis that secondary hybridization events can lead to asexual lineages of increased ploidy when favorable combinations of parental genomes are assembled. We anticipate that these animals will be a critical tool in understanding the mechanisms underlying the origin and subsequent evolution of asexual amniotes.
动物的物种形成通常涉及到遗传交流的外在障碍，随后是足够的遗传变异积累，以阻碍随后的有性杂交。由性祖先后代种间杂交产生的全雌性鞭尾蜥蜴物种就是该规则的例外。在这里，新出现的物种瞬间获得了一种新的基因型，它结合了来自两个不同物种的独特等位基因，而孤雌生殖的繁殖构成了遗传交流的有效内在障碍。二倍体孤雌生殖雌性与有性物种雄性的受精产生了几个三倍体物种，但这些瞬间的物种形成事件既没有在自然界中观察到，也没有在实验室中重建。在这里，我们报告了四倍体物种的四个自我维持的克隆谱系的产生，这是通过受精三倍体卵母细胞从孤雌生殖的 Aspidoscelis exsanguis 与来自 Aspidoscelis inornata 的单倍体精子产生的。分子和细胞学分析证实了杂种的遗传同一性，并揭示了雌性保留了与其三倍体母亲特征性的孤雌生殖繁殖能力。四倍体雌性已经建立了自我维持的克隆谱系，现在已经是第三代了。我们的结果证实了这样一种假设，即当有利的亲本基因组组合在一起时，二次杂交事件可能导致增加的多倍体的无性谱系。我们预计这些动物将成为理解无脊椎动物无性起源和随后进化的机制的关键工具。
