Burridge C P, Craw D, Waters J M
Department of Zoology, University of Otago, P.O. Box 56, Dunedin, New Zealand.
Evolution. 2006 May;60(5):1038-49.
River capture is potentially a key geomorphological driver of range expansion and cladogenesis in freshwater-limited taxa. While previous studies of freshwater fish, in particular, have indicated strong relationships between historical river connections and phylogeographic pattern, their analyses have been restricted to single taxa and geological hypotheses were typically constructed a posteriori. Here we assess the broader significance of river capture among taxa by testing multiple species for the genetic signature of a recent river capture event in New Zealand. During the Quaternary an upper tributary of the Clarence River system was diverted into the headwaters of the Wairau River catchment. Mitochondrial DNA (control region and cytochrome b) sequencing of two native galaxiid fishes (Galaxias vulgaris and Galaxias divergens) supports headwater exchange: populations from the Clarence and Wairau Rivers are closely related sister-groups, whereas samples from the geographically intermediate Awatere River are genetically divergent. The upland bully Gobiomorphus breviceps (Eleotridae), in contrast, lacks a genetic signature of the capture event. We hypothesize that there is an increased likelihood of observing genetic signatures from river capture events when they facilitate range expansion, as is inferred for the two galaxiid taxa studied here. When river capture merely translocates genetic lineages among established populations, by contrast, we suggest that the genetic signature of capture is less likely to be retained, as might be inferred for G. breviceps. Rates of molecular evolution calibrated against this recent event were elevated relative to traditional estimates, consistent with the contribution of polymorphisms to branch lengths at shallow phylogenetic levels prior to fixation by purifying selection and drift.
河流袭夺可能是淡水受限类群范围扩张和物种形成的关键地貌驱动因素。特别是，以往对淡水鱼的研究表明，历史上的河流连通性与系统发育地理格局之间存在密切关系，但这些分析仅限于单一类群，而且地质假说通常是事后构建的。在这里，我们通过测试多个物种，来评估新西兰近期一次河流袭夺事件的遗传特征，以此来评估河流袭夺在不同类群中的更广泛意义。在第四纪期间，克拉伦斯河水系的一条上游支流被改道流入怀劳河集水区的源头。对两种本地南乳鱼（普通南乳鱼和歧异南乳鱼）的线粒体DNA（控制区和细胞色素b）进行测序，支持了源头区域的交流：克拉伦斯河和怀劳河的种群是密切相关的姐妹群，而来自地理上处于中间位置的阿瓦特雷河的样本在基因上则存在差异。相比之下，高地无须鳚（塘鳢科）则缺乏这次袭夺事件的遗传特征。我们推测，当河流袭夺促进范围扩张时，就像我们在这里研究的两种南乳鱼类群那样，观察到河流袭夺事件遗传特征的可能性会增加。相比之下，当河流袭夺仅仅是在已有的种群之间转移遗传谱系时，我们认为袭夺的遗传特征不太可能保留下来，高地无须鳚可能就是这种情况。根据这一近期事件校准的分子进化速率相对于传统估计有所提高，这与多态性在通过纯化选择和漂变固定之前对浅系统发育水平分支长度的贡献是一致的。
