Department of Biology, Brigham Young University, Provo, Utah, United States of America.
PLoS One. 2012;7(6):e37105. doi: 10.1371/journal.pone.0037105. Epub 2012 Jun 7.
Multiple loci and population genetic methods were employed to study the phylogeographic history of the Patagonian freshwater crab Aegla neuquensis (Aeglidae: Decopoda). This taxon occurs in two large river systems in the Patagonian Steppe, from the foothills of the Andes Mountains east to the Atlantic Ocean.
METHODOLOGY/PRINCIPAL FINDINGS: A nuclear phylogeny and multilocus nested clade phylogeographic analysis detected a fragmentation event between the Negro and Chico-Chubut river systems. This event occurred approximately 137 thousand years ago. An isolation-with-migration analysis and maximum-likelihood estimates of gene flow showed asymmetrical exchange of genetic material between these two river systems exclusively in their headwaters. We used information theory to determine the best-fit demographic history between these two river systems under an isolation-with-migration model. The best-fit model suggests that the Negro and the ancestral populations have the same effective population sizes; whereas the Chico-Chubut population is smaller and shows that gene flow from the Chico-Chubut into the Negro is four times higher than in the reverse direction. Much of the Chico-Chubut system appears to have only been recently colonized while the Negro populations appear to have been in place for most of the evolutionary history of this taxon.
CONCLUSIONS/SIGNIFICANCE: Due to mitochondrial introgression, three nuclear loci provided different phylogeographic resolution than the three mitochondrial genes for an ancient fragmentation event observed in the nuclear phylogeny. However, the mitochondrial locus provided greater resolution on more recent evolutionary events. Our study, therefore, demonstrates the need to include both nuclear and mitochondrial loci for a more complete understanding of evolutionary histories and associated phylogeographic events. Our results suggest that gene flow between these systems, before and after fragmentation was through periodic paleolakes that formed in the headwaters region. Fragmentation between the Negro and Chico-Chubut systems was driven by the disappearance of these paleolakes during the Patagonian Glaciation.
采用多个基因座和群体遗传学方法研究了巴塔哥尼亚淡水蟹 Aegla neuquensis（Aeglidae：Decopoda）的系统地理历史。这个分类单元分布于巴塔哥尼亚草原的两个大河系统，从安第斯山脉的山麓向东延伸到大西洋。
方法/主要发现：核系统发育和多点嵌套支系地理遗传分析检测到 Negro 和 Chico-Chubut 河流系统之间发生了碎裂事件。该事件发生在大约 13.7 万年前。隔离-迁移分析和基因流的最大似然估计显示，这两个河流系统之间的遗传物质不对称交换，仅在其源头发生。我们使用信息理论来确定这两个河流系统在隔离-迁移模型下最佳的种群历史拟合模型。最佳拟合模型表明 Negro 和祖先群体具有相同的有效种群大小；而 Chico-Chubut 群体较小，表明来自 Chico-Chubut 的基因流进入 Negro 的速度是相反方向的四倍。Chico-Chubut 系统的大部分似乎是最近才被殖民的，而 Negro 群体在这个分类单元的大部分进化历史中都已经存在。
结论/意义：由于线粒体基因渗入，三个核基因座提供的系统地理分辨率与核系统发育中观察到的古老碎裂事件的三个线粒体基因不同。然而，线粒体基因座提供了对更近进化事件的更高分辨率。因此，我们的研究表明，为了更全面地了解进化历史和相关的系统地理事件，需要同时包括核和线粒体基因座。我们的研究结果表明，在碎裂之前和之后，这些系统之间的基因流是通过在源头区域形成的周期性古湖泊进行的。 Negro 和 Chico-Chubut 系统之间的碎裂是由巴塔哥尼亚冰川作用期间这些古湖泊的消失所驱动的。
