Farias Izeni Pires, Hrbek Tomas
Universidade Federal do Amazonas, Departamento de Biologia, Laboratório de Evolução e Genética Animal, Av. Rodrigo Octávio Jordão Ramos, 3000, 69077-000 Manaus, AM, Brazil.
Mol Phylogenet Evol. 2008 Oct;49(1):32-43. doi: 10.1016/j.ympev.2008.05.033. Epub 2008 Jun 3.
We carried out a phylogeograhic and population genetic analysis of fishes of the taxonomically contentious genus Symphysodon from the Amazon basin in order to test hypotheses of relationships among taxonomic units, and potential processes driving diversification within this genus. We sampled 334 individuals of the genus Symphysodon from 24 localities that span the complete geographic distribution of this genus. The sampling scheme included all known phenotypic groups, species and subspecies. Analyses were based on 474 bp of the mitochondrial control region and 1443 bp of the exon 3 of RAG1 gene. We observed 102 mtDNA haplotypes defined by 89 segregating sites, and 5 nuDNA alleles defined by three segregating sites. Maximum-likelihood, Bayesian-inference and statistical parsimony analyses revealed three well defined monophyletic groups. These clades corresponded to the 'green' and 'blue' groups of Symphysodon aequifasciatus, and to a previously morphologically unrecognized clade from the Xingu River drainage. These three clades were nested within a paraphyletic assemblage consisting of the 'brown' group of S. aequifasciatus and of both described subspecies of S. discus, the 'Heckel' and the 'abacaxi' discus. Nuclear allele sharing was observed among groups, but there were significant differences in frequencies. We inferred several processes including past fragmentation among groups, and restricted gene flow with isolation by distance within the paraphyletic 'brown+Heckel+abacaxi' groups, and suggest that differences among the 'blue', 'Heckel' and 'brown' groups are potentially maintained by differences in water chemistry preferences. We further inferred colonization of the western Amazon basin by an ancestor of the 'green' clade. The 'green' group was the only group with a pattern of haplotype distribution consistent of a demographic expansion, and the divergence of this clade from other groups of discus was consistent with recent geologic evidence on the breach of the Purus Arch which separates western Amazon from eastern Amazon. We further hypothesized that the differentiation of the 'Xingu' clade could be due to vicariance events resulting from Pleistocene sea level, and thus Amazon River level fluctuations. We discuss the bearings of our results on the current taxonomy of this group, and on the biological reality of the different forms, subspecies and species of Symphysodon concluding that we are probably observing a process of diversification, and therefore taxonomy will remain contentious.
我们对来自亚马逊河流域分类存在争议的盘丽鱼属鱼类进行了系统地理学和种群遗传学分析，以检验分类单元之间关系的假设，以及推动该属内物种多样化的潜在过程。我们从24个地点采集了334个盘丽鱼属个体样本，这些地点涵盖了该属的完整地理分布范围。抽样方案包括所有已知的表型组、物种和亚种。分析基于线粒体控制区的474 bp和RAG1基因外显子3的1443 bp。我们观察到由89个分离位点定义的102个线粒体DNA单倍型，以及由3个分离位点定义的5个核DNA等位基因。最大似然法、贝叶斯推断和统计简约法分析揭示了三个定义明确的单系类群。这些分支分别对应于盘丽鱼的“绿色”和“蓝色”群体，以及来自欣古河流域一个以前在形态学上未被识别的分支。这三个分支嵌套在一个并系组合中，该组合由盘丽鱼的“棕色”群体以及盘丽鱼的两个已描述亚种“黑格尔”盘丽鱼和“阿巴卡希”盘丽鱼组成。在各群体之间观察到核等位基因共享，但频率存在显著差异。我们推断了几个过程，包括群体之间过去的隔离，以及在并系的“棕色+黑格尔+阿巴卡希”群体中存在距离隔离导致的有限基因流，并表明“蓝色”、“黑格尔”和“棕色”群体之间的差异可能是由对水化学偏好的差异维持的。我们进一步推断“绿色”分支的一个祖先曾殖民亚马逊河流域西部。“绿色”群体是唯一具有与种群扩张一致的单倍型分布模式的群体，并且该分支与其他盘丽鱼群体的分化与最近关于分隔亚马逊西部和东部的普鲁斯拱门破裂的地质证据一致。我们进一步假设“欣古”分支的分化可能是由于更新世海平面导致的地理隔离事件，进而导致亚马逊河水位波动。我们讨论了我们的结果对该类群当前分类法以及盘丽鱼不同形态、亚种和物种的生物学真实性的影响，得出的结论是我们可能正在观察一个多样化的过程，因此分类法仍将存在争议。
