RESUMEN
The relationship between Scleractinia and Corallimorpharia, Orders within Anthozoa distinguished by the presence of an aragonite skeleton in the former, is controversial. Although classically considered distinct groups, some phylogenetic analyses have placed the Corallimorpharia within a larger Scleractinia/Corallimorpharia clade, leading to the suggestion that the Corallimorpharia are "naked corals" that arose via skeleton loss during the Cretaceous from a Scleractinian ancestor. Scleractinian paraphyly is, however, contradicted by a number of recent phylogenetic studies based on mt nucleotide (nt) sequence data. Whereas the "naked coral" hypothesis was based on analysis of the sequences of proteins encoded by a relatively small number of mt genomes, here a much-expanded dataset was used to reinvestigate hexacorallian phylogeny. The initial observation was that, whereas analyses based on nt data support scleractinian monophyly, those based on amino acid (aa) data support the "naked coral" hypothesis, irrespective of the method and with very strong support. To better understand the bases of these contrasting results, the effects of systematic errors were examined. Compared to other hexacorallians, the mt genomes of "Robust" corals have a higher (A+T) content, codon usage is far more constrained, and the proteins that they encode have a markedly higher phenylalanine content, leading us to suggest that mt DNA repair may be impaired in this lineage. Thus the "naked coral" topology could be caused by high levels of saturation in these mitochondrial sequences, long-branch effects or model violations. The equivocal results of these extensive analyses highlight the fundamental problems of basing coral phylogeny on mitochondrial sequence data.
Asunto(s)
Antozoos/genética , ADN Mitocondrial/genética , Genoma Mitocondrial/genética , Proteínas Mitocondriales/genética , Filogenia , Aminoácidos/genética , Animales , Antozoos/clasificación , Composición de Base/genética , Codón/genética , ADN Mitocondrial/química , ARN Ribosómico/genética , ARN Ribosómico 16S/genética , ARN de Transferencia de Metionina/genética , ARN de Transferencia de Triptófano/genética , Análisis de Secuencia de ADN , Especificidad de la EspecieRESUMEN
We investigated mitochondrial and nuclear DNA in the small tyrant-flycatcher genus Zimmerius (Tyrannidae) and show that molecular data are in strong disagreement with morphology-based taxonomy, but in good concordance with vocal characters. Our molecular data identified two independent cases of well-supported polyphyletic species arrangements within this genus that indicate the following taxonomic changes: elevation of Z. acer and Z. albigularis to species level, separation of northern populations of Z. chrysops as a species and inclusion of southern populations of Z. chrysops into Z. viridiflavus. Although polyphyly has rarely been encountered in bird systematics it has previously been shown for two other tyrannid genera and suggests that tyrannid taxonomy may be poorly resolved, presumably as a consequence of the conserved plumage patterns observed in many tyrannid genera. Our study suggests that vocalizations can be a better indicator of taxonomic limits than plumage pattern in tyrannids.