Department of Zoology, Graduate School of Science, Kyoto University, Sakyo, Kyoto 606-8502, Japan.
BMC Evol Biol. 2010 Jan 25;10:21. doi: 10.1186/1471-2148-10-21.
The family Polypteridae, commonly known as "bichirs", is a lineage that diverged early in the evolutionary history of Actinopterygii (ray-finned fish), but has been the subject of far less evolutionary study than other members of that clade. Uncovering patterns of morphological change within Polypteridae provides an important opportunity to evaluate if the mechanisms underlying morphological evolution are shared among actinoptyerygians, and in fact, perhaps the entire osteichthyan (bony fish and tetrapods) tree of life. However, the greatest impediment to elucidating these patterns is the lack of a well-resolved, highly-supported phylogenetic tree of Polypteridae. In fact, the interrelationships of polypterid species have never been subject to molecular phylogenetic analysis. Here, we infer the first molecular phylogeny of bichirs, including all 12 recognized species and multiple subspecies using Bayesian analyses of 16S and cyt-b mtDNA. We use this mitochondrial phylogeny, ancestral state reconstruction, and geometric morphometrics to test whether patterns of morphological evolution, including the evolution of body elongation, pelvic fin reduction, and craniofacial morphology, are shared throughout the osteichthyan tree of life.
Our molecular phylogeny reveals 1) a basal divergence between Erpetoichthys and Polypterus, 2) polyphyly of P. endlicheri and P. palmas, and thus 3) the current taxonomy of Polypteridae masks its underlying genetic diversity. Ancestral state reconstructions suggest that pelvic fins were lost independently in Erpetoichthys, and unambiguously estimate multiple independent derivations of body elongation and shortening. Our mitochondrial phylogeny suggested species that have lower jaw protrusion and up-righted orbit are closely related to each other, indicating a single transformation of craniofacial morphology.
The mitochondrial phylogeny of polypterid fish provides a strongly-supported phylogenetic framework for future comparative evolutionary, physiological, ecological, and genetic analyses. Indeed, ancestral reconstruction and geometric morphometric analyses revealed that the patterns of morphological evolution in Polypteridae are similar to those seen in other osteichthyans, thus implying the underlying genetic and developmental mechanisms responsible for those patterns were established early in the evolutionary history of Osteichthyes. We propose developmental and genetic mechanisms to be tested under the light of this new phylogenetic framework.
多鳍鱼科（俗称“骨舌鱼”）是肉鳍鱼总鳍鱼类的一个分支，在肉鳍鱼类的进化历史中很早就出现了分化，但与该分支的其他成员相比，进化研究的程度要低得多。揭示多鳍鱼科内部形态变化的模式提供了一个重要的机会，可以评估形态进化的机制是否在肉鳍鱼类中共享，事实上，也许在整个硬骨鱼（骨鱼和四足动物）的生命树中都是如此。然而，阐明这些模式的最大障碍是缺乏一个分辨率高、支持度强的多鳍鱼科系统发育树。事实上，多鳍鱼科物种的种间关系从未进行过分子系统发育分析。在这里，我们使用 16S 和细胞色素 b mtDNA 的贝叶斯分析推断出骨舌鱼的第一个分子系统发育，包括所有 12 种已识别的物种和多个亚种。我们使用这个线粒体系统发育、祖先状态重建和几何形态测量学来测试形态进化的模式，包括身体伸长、臀鳍退化和颅面形态的进化，是否在整个硬骨鱼的生命树中共享。
我们的分子系统发育揭示了 1） 厄尔皮托鱼和多鳍鱼之间的基本分歧，2） 波氏多鳍鱼和帕玛多鳍鱼的多系性，因此 3） 多鳍鱼科目前的分类掩盖了其潜在的遗传多样性。祖先状态重建表明，臀鳍在厄尔皮托鱼中独立丢失，并明确估计了身体伸长和缩短的多次独立衍生。我们的线粒体系统发育表明，具有下颌突出和直立眶的物种彼此密切相关，表明颅面形态发生了单一的转变。
多鳍鱼的线粒体系统发育为未来的比较进化、生理、生态和遗传分析提供了一个强有力的支持的系统发育框架。事实上，祖先重建和几何形态测量分析表明，多鳍鱼科的形态进化模式与其他硬骨鱼相似，因此暗示了负责这些模式的遗传和发育机制在硬骨鱼的进化历史早期就已经建立。我们提出了一些发育和遗传机制，以在这个新的系统发育框架下进行测试。
