Molecular phylogenetics and phenotypic reassessment of the Ramphotrigon flycatchers: deep paraphyly in the context of an intriguing biogeographic scenario

Abstract

The tyrant-flycatchers (Tyrannidae) are the largest family of birds in the New World. Although their phylogenetic relationships have been deeply studied based on phenotypic and genetic characters, several systematic uncertainties still exist. In particular, the affinities within the South American genus Ramphotrigon and its close relationship with the Mexican-endemic Deltarhynchus flammulatus remain unresolved. Here we performed a taxonomic assessment of this intriguing relationship including, for the first time, representatives of all three Ramphotrigon species and the monotypic Deltarhynchus. We carried out phylogenetic analyses based on three mitochondrial markers and one autosomal nuclear intron, and complemented the genetic evidence with the study of morphological and plumage coloration differentiation, in order to provide a more in-depth reassessment of the Ramphotrigon–Deltarhynchus relationship in general and the genus Ramphotrigon in particular. Genetic data showed that Ramphotrigon is paraphyletic as currently defined, with R. fuscicauda and R. ruficauda being more closely related to D. flammulatus than to R. megacephalum. This paraphyletic relationship was recovered with maximum support based on mitochondrial and nuclear markers. Ramphotrigon megacephalum evidenced a deep genetic divergence from its two congeners and D. flammulatus, comparable to that between the first one and other tyrannids. Ramphotrigon megacephalum was also significantly different from D. flammulatus, R. fuscicauda and R. ruficauda in external morphology and plumage coloration. On the other hand, D. flammulatus, R. fuscicauda and R. ruficauda showed almost no differences in the morphological variables analyzed. In this context, we believe that a taxonomic reorganization of this group is necessary. One possibility would be to transfer D. flammulatus to the genus Ramphotrigon and to assign R. megacephalum to a new genus with at least two species. Lastly, we propose a biogeographic model for the evolutionary history of Ramphotrigon and Deltarhynchus in South and Middle America over the past 12 million years.