Data from: Multiple independent colonizations into the Congo Basin during the continental radiation of African Mastacembelus spiny eels

Aim: There has been recent interest in the origin and assembly of continental biotas based on densely sampled species-level clades, however, studies from African freshwaters are few so that the commonality of macroevolutionary patterns and processes among continental clades remain to be tested. Within the Afrotropics, the Congo Basin contains the highest diversity of riverine fishes, yet it is unclear how this fauna was assembled. To address this, and the diversification dynamics of a continental radiation, we focus on African Mastacembelus spiny eels.
Location: Afrotropical freshwaters.
Methods: The most complete molecular phylogeny to date was reconstructed for African spiny eels. Divergence times were estimated applying a Bayesian relaxed clock comparing fossil and geological calibrations across nuclear and mitochondrial trees. Biogeographic reconstructions, applying a dispersal–extinction–cladogenesis model and lineage diversification dynamics were examined.
Results: Spiny eels originated in Asia and colonized Africa c. 15.4 Ma (95% HPD: 23.9–8.8 Ma) from which their subsequent radiation across the Afrotropics was best fitted by a constant rate model. Ancestral state estimation identified multiple colonization events into the Congo Basin, whereas all other regions were likely to have been colonized once indicating considerable geographic constraints. Application of the fossil calibration gave similar age estimates across datasets, whereas a geological calibration estimated considerably older nuclear divergences.
Main conclusions: Despite profound environmental events during the evolutionary history of the group, there is no evidence for rapid lineage diversification. This finding supports several recent studies on tropical continental radiations that contrast to the common pattern of density-dependent diversification. We further show that dispersal has occurred into, as well as out of the Congo Basin, indicating the importance of this region in the generation of biodiversity.

研究目的：近年来，基于高密度采样的物种级支系开展大陆生物区系起源与组装的研究日益受到关注，但针对非洲淡水生态系统的相关研究仍较为匮乏，因此大陆支系间宏观演化模式与过程的共性仍有待验证。在非洲热带区（Afrotropics）范围内，刚果盆地拥有最为丰富的河川鱼类多样性，但目前学界仍不清楚该区域的动物区系是如何形成的。为解答这一问题，并揭示大陆辐射类群的演化动态，本研究聚焦于非洲刺鳅属（Mastacembelus）刺鳅。
研究区域：非洲热带区淡水水域。
研究方法：本研究重建了目前最为完整的非洲刺鳅分子系统发育树。采用贝叶斯宽松分子钟（Bayesian relaxed clock）方法，结合核基因与线粒体基因树的化石校准与地质校准方案，估算类群的分化时间。同时应用扩散-灭绝-分支形成（dispersal–extinction–cladogenesis, DEC）模型开展生物地理重建，并分析支系的演化动态。
研究结果：刺鳅起源于亚洲，于约15.4百万年前（Ma）（95%最高后验密度（HPD）区间：23.9–8.8百万年前）扩散至非洲；随后在非洲热带区的辐射演化最符合恒定速率模型。祖先状态重建结果显示，刚果盆地曾发生多次殖民事件，而其他所有区域均仅发生过一次殖民事件，这表明类群扩散存在较强的地理限制。化石校准方案在不同数据集下得到的分化时间估算结果较为一致，而地质校准方案则估算得到更为古老的核基因分化时间。
主要结论：尽管该类群的演化历史中曾伴随剧烈的环境剧变，但并未发现支系快速分化的证据。这一结果与多项针对热带大陆辐射类群的近期研究结论一致，即这类类群的分化模式并不符合常见的密度制约型分化规律。本研究进一步证实，刺鳅类群既存在向刚果盆地的扩散事件，也存在从该盆地向外的扩散，这表明刚果盆地在生物多样性产生过程中具有重要作用。