Choi Jae Young, Aquadro Charles F
Department of Molecular Biology and Genetics, Cornell University
Department of Molecular Biology and Genetics, Cornell University.
Mol Biol Evol. 2014 Sep;31(9):2457-71. doi: 10.1093/molbev/msu204. Epub 2014 Jun 28.
The endosymbiotic bacteria Wolbachia pipientis is known to infect a wide range of arthropod species yet less is known about the coevolutionary history it has with its hosts. Evidence of highly identical W. pipientis strains in evolutionary divergent hosts suggests horizontal transfer between hosts. For example, Drosophila ananassae is infected with a W. pipientis strain that is nearly identical in sequence to a strain that infects both D. simulans and D. suzukii, suggesting recent horizontal transfer among these three species. However, it is unknown whether the W. pipientis strain had recently invaded all three species or a more complex infectious dynamic underlies the horizontal transfers. Here, we have examined the coevolutionary history of D. ananassae and its resident W. pipientis to infer its period of infection. Phylogenetic analysis of D. ananassae mitochondrial DNA and W. pipientis DNA sequence diversity revealed the current W. pipientis infection is not recent. In addition, we examined the population genetics and molecular evolution of several germline stem cell (GSC) regulating genes of D. ananassae. These studies reveal significant evidence of recent and long-term positive selection at stonewall in D. ananassae, whereas pumillio showed patterns of variation consistent with only recent positive selection. Previous studies had found evidence for adaptive evolution of two key germline differentiation genes, bag of marbles (bam) and benign gonial cell neoplasm (bgcn), in D. melanogaster and D. simulans and proposed that the adaptive evolution at these two genes was driven by arms race between the host GSC and W. pipientis. However, we did not find any statistical departures from a neutral model of evolution for bam and bgcn in D. ananassae despite our new evidence that this species has been infected with W. pipientis for a period longer than the most recent infection in D. melanogaster. In the end, analyzing the GSC regulating genes individually showed two of the seven genes to have evidence of selection. However, combining the data set and fitting a specific population genetic model significant proportion of the nonsynonymous sites across the GSC regulating genes were driven to fixation by positive selection. Clearly the GSC system is under rapid evolution and potentially multiple drivers are causing the rapid evolution.
内共生细菌沃尔巴克氏体（Wolbachia pipientis）已知可感染多种节肢动物物种，但人们对其与宿主的共同进化历史了解较少。在进化上差异很大的宿主中发现高度相同的沃尔巴克氏体菌株，这表明存在宿主间的水平转移。例如，拟暗果蝇（Drosophila ananassae）感染了一种沃尔巴克氏体菌株，其序列与感染拟果蝇（D. simulans）和铃木果蝇（D. suzukii）的菌株几乎相同，这表明这三个物种之间最近发生了水平转移。然而，尚不清楚该沃尔巴克氏体菌株是最近侵入了这三个物种，还是水平转移背后存在更复杂的感染动态。在这里，我们研究了拟暗果蝇及其常驻沃尔巴克氏体的共同进化历史，以推断其感染时期。对拟暗果蝇线粒体DNA和沃尔巴克氏体DNA序列多样性的系统发育分析表明，目前的沃尔巴克氏体感染并非近期发生。此外，我们研究了拟暗果蝇几个生殖系干细胞（GSC）调控基因的群体遗传学和分子进化。这些研究揭示了拟暗果蝇中stonewall基因近期和长期正选择的显著证据，而 pumillio 显示出的变异模式仅与近期正选择一致。先前的研究发现了黑腹果蝇（D. melanogaster）和拟果蝇中两个关键生殖系分化基因——大理石袋（bam）和良性生殖细胞瘤（bgcn）适应性进化的证据，并提出这两个基因的适应性进化是由宿主生殖系干细胞和沃尔巴克氏体之间的军备竞赛驱动的。然而，尽管我们有新证据表明拟暗果蝇感染沃尔巴克氏体的时间比黑腹果蝇最近的感染时间更长，但我们并未发现拟暗果蝇中bam和bgcn基因的进化偏离中性模型。最后，单独分析生殖系干细胞调控基因时，七个基因中有两个有选择的证据。然而，合并数据集并拟合特定的群体遗传模型后，生殖系干细胞调控基因中相当比例的非同义位点被正选择驱动至固定状态。显然，生殖系干细胞系统正在快速进化，可能有多种驱动因素导致这种快速进化。
