An unbiased molecular approach using 3’UTRs resolves the avian family-level tree of life

Presumably, due to a rapid early diversification, major parts of the higher-level phylogeny of birds are still resolved controversially in different analyses or are considered unresolvable. To address this problem, we produced an avian tree of life, which includes molecular sequences of one or several species of ∼ 90% of the currently recognized family-level taxa (429 species, 379 genera) including all 106 for the non-passerines and 115 for the passerines (Passeriformes). The unconstrained analyses of noncoding 3-prime untranslated region (3’UTR) sequences and those of coding sequences yielded different trees. In contrast to the coding sequences, the 3’UTR sequences resulted in a well-resolved and stable tree topology. The 3’UTR contained, unexpectedly, transcription factor binding motifs that were specific for different higher-level taxa. In this tree, grebes and flamingos are the sister clade of all other Neoaves, which are subdivided into five major clades. All non-passerine taxa were placed with robust statistical support including the long-time enigmatic hoatzin (Opisthocomiformes), which was found being the sister taxon of the Caprimulgiformes. The comparatively late radiation of family-level clades of the songbirds (oscine Passeriformes) contrasts with the attenuated diversification of non-passeriform taxa since the early Miocene. This correlates with the evolution of vocal production learning, an important speciation factor, which is ancestral for songbirds and evolved convergent only in hummingbirds and parrots. Since 3’UTR-based phylotranscriptomics resolved the avian family-level tree of life, we suggest that this procedure will also resolve the all-species avian tree of life

鉴于鸟类早期快速辐射演化，其高级阶元系统发育（higher-level phylogeny）的多数核心分支在不同分析中仍存在争议，甚至被认为无法解析。为解决这一科研难题，本研究构建了鸟类生命之树（avian tree of life），该数据集涵盖了当前已确认的约90%科级分类群的1个或多个物种的分子序列，涉及429个物种、379个属，其中包含非雀形目全部106个科以及雀形目（Passeriformes）的115个科。研究人员分别对非编码3'非翻译区（noncoding 3-prime untranslated region，3’UTR）序列与编码序列开展无约束分析，得到了两套截然不同的系统发育树。与编码序列的分析结果相悖，基于3’UTR序列的分析得到了分辨率优异且稳定性极强的系统发育拓扑结构。令人意外的是，3’UTR区域携带有针对不同高级阶元类群的特异性转录因子结合基序。在本研究构建的系统发育树中，䴙䴘与红鹳构成了其余新鸟类（Neoaves）的姊妹支，而新鸟类可进一步划分为5个主要支系。所有非雀形目类群的系统发育位置均获得了强有力的统计学支持，其中包括长期以来颇具分类争议的麝雉（Opisthocomiformes）——本研究证实其为夜鹰目（Caprimulgiformes）的姊妹群。鸣禽亚目（oscine Passeriformes）科级类群的辐射演化发生时间相对较晚，而自中新世早期以来非雀形目类群的演化辐射则相对减弱。这一现象与发声学习（vocal production learning）这一重要成种因子的演化密切相关：发声学习为鸣禽的祖征，且仅在蜂鸟与鹦鹉中独立演化而来。鉴于基于3’UTR序列的转录组系统发育学（phylotranscriptomics）成功解析了鸟类科级生命之树，我们推测该方法同样可用于构建覆盖所有鸟类物种的完整生命之树。