Molecular phylogenetics reveals convergent evolution in lower Congo River spiny eels.
Molecular phylogenetics reveals convergent evolution in lower Congo River spiny eels.
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DOI：
10.1186/s12862-015-0507-x
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发表时间：
2015-10-15
影响因子：
3.4
通讯作者：
Stiassny ML
中科院分区：
文献类型：
--
作者：
Alter SE;Brown B;Stiassny ML
刚果河下游 (LCR) 是刚果盆地物种多样性和特有性的地区，其中包括许多种类的刺鳗（Mastacembelus 属）。其中四种表现出独特的表型，其特征是深深嵌入头部的视神经球大大减少（隐眼症）和黑色素沉着减少（或消失）等特征。在许多不相关的鱼类家族的成员中也发现了惊人相似的隐眼表型，这强烈表明趋同进化的可能性。然而，人们对形成 LCR Mastacembelus 多样化的进化过程、它们的生物地理起源或 LCR 殖民发生的时间知之甚少。我们对在刚果河下游收集的 Mastacembelus 物种的线粒体和核基因进行了测序，并将它们与作为外群体的其他非洲物种和亚洲代表进行了比较。我们使用最大似然和贝叶斯系统发育推断分析了序列数据。贝叶斯和最大似然系统发育分析以及用于物种树重建的贝叶斯合并方法揭示了地方性 LCR 刺鳗源自两个独立的起源，清楚地证明了隐眼表型的趋同进化。 Mastacembelus crassus、M. aviceps 和 M. simbi 形成一个分支，与非洲南部、东部和中部发现的物种有亲缘关系。出乎意料的是，M. brichardi 和 brachyrhinus 属于大约在坦噶尼基亚湖 (LT) 特有的一个分支。 LCR 以东 1500 公里处。分歧年代测定表明这两个 LCR 地方性分支的年龄存在显着差异。 crassus 群体的年龄估计约为 4 Myr，而 brichardi-brachyrhinus 祖先在 LCR 上的定植则要晚得多，可追溯到约 0.5 Myr。这里介绍的刺鳗的系统发育框架是第一个包含 LCR 物种的系统发育框架，表明隐眼症和相关特征在 Mastacembelus 中至少进化了两次：一次在 M. brichardi 中，至少一次在 M. crassus 分支中进化。多样化的时间与 LCR 现代高能流条件的开始以及以前对特有慈鲷的研究大致一致。考虑到这些物种之间表型的极端差异，M. brichardi 和 M. brachyrhinus 之间的密切遗传关系尤其值得注意，并且需要进行额外的工作来更好地了解该分支多样化的进化历史。这里提出的研究结果表明，LCR 刺鳗具有强大的多性状趋同性，表明极端的选择压力塑造了该地区特有物种的众多表型属性。本文的在线版本 (doi:10.1186/s12862-015-0507-x) 包含补充材料，可供授权用户使用。
The lower Congo River (LCR) is a region of exceptional species diversity and endemism in the Congo basin, including numerous species of spiny eels (genus Mastacembelus). Four of these exhibit distinctive phenotypes characterized by greatly reduced optic globes deeply embedded into the head (cryptophthalmia) and reduced (or absent) melanin pigmentation, among other characteristics. A strikingly similar cryptophthalmic phenotype is also found in members of a number of unrelated fish families, strongly suggesting the possibility of convergent evolution. However, little is known about the evolutionary processes that shaped diversification in LCR Mastacembelus, their biogeographic origins, or when colonization of the LCR occurred. We sequenced mitochondrial and nuclear genes from Mastacembelus species collected in the lower Congo River, and compared them with other African species and Asian representatives as outgroups. We analyzed the sequence data using Maximum Likelihood and Bayesian phylogenetic inference. Bayesian and Maximum Likelihood phylogenetic analyses, and Bayesian coalescent methods for species tree reconstruction, reveal that endemic LCR spiny eels derive from two independent origins, clearly demonstrating convergent evolution of the cryptophthalmic phenotype. Mastacembelus crassus, M. aviceps, and M. simbi form a clade, allied to species found in southern, eastern and central Africa. Unexpectedly, M. brichardi and brachyrhinus fall within a clade otherwise endemic to Lake Tanganikya (LT) ca. 1500 km east of the LCR. Divergence dating suggests the ages of these two clades of LCR endemics differ markedly. The age of the crassus group is estimated at ~4 Myr while colonization of the LCR by the brichardi-brachyrhinus progenitor was considerably more recent, dated at ~0.5 Myr. The phylogenetic framework of spiny eels presented here, the first to include LCR species, demonstrates that cryptophthalmia and associated traits evolved at least twice in Mastacembelus: once in M. brichardi and at least once in the M. crassus clade. Timing of diversification is broadly consistent with the onset of modern high-energy flow conditions in the LCR and with previous studies of endemic cichlids. The close genetic relationship between M. brichardi and M. brachyrhinus is particularly notable given the extreme difference in phenotype between these species, and additional work is needed to better understand the evolutionary history of diversification in this clade. The findings presented here demonstrate strong, multi-trait convergence in LCR spiny eels, suggesting that extreme selective pressures have shaped numerous phenotypic attributes of the endemic species of this region. The online version of this article (doi:10.1186/s12862-015-0507-x) contains supplementary material, which is available to authorized users.