Multiple species and deep genomic divergences despite little phenotypic differentiation in an ancient Neotropical songbird, Tunchiornis ochraceiceps (Sclater, 1860) (Aves: Vireonidae).

Several bird taxa have been recently described or elevated to full species and almost twice as many bird species than are currently recognized may exist. Defining species is one of the most basic and important issues in biological science because unknown or poorly defined species hamper subsequent studies. Here, we evaluate the species limits and evolutionary history of Tunchiornis ochraceiceps-a widespread forest songbird that occurs in the lowlands of Central America, Chocó and Amazonia-using an integrative approach that includes plumage coloration, morphometrics, vocalization and genomic data. The species has a relatively old crown age (~9 Ma) and comprises several lineages with little, if any, evidence of gene flow among them. We propose a taxonomic arrangement composed of four species, three with a plumage coloration diagnosis and one deeply divergent cryptic species. Most of the remaining lineages have variable but unfixed phenotypic characters despite their relatively old origin. This decoupling of genomic and phenotypic differentiation reveals a remarkable case of phenotypic conservatism, possibly due to strict habitat association. Lineages are geographically delimited by the main Amazonian rivers and the Andes, a pattern observed in studies of other understory upland forest Neotropical birds, although phylogenetic relationships and divergence times among populations are idiosyncratic.

Paleoclimatic evolution as the main driver of current genomic diversity in the widespread and polymorphic Neotropical songbird Arremon taciturnus.

Several factors have been proposed as drivers of species diversification in the Neotropics, including environmental heterogeneity, the development of drainage systems and historical changes in forest distribution due to climatic oscillations. Here, we investigate which drivers contributed to the evolutionary history and current patterns of diversity of a polymorphic songbird (Arremon taciturnus) that is widely distributed in Amazonian and Atlantic forests as well as in Cerrado gallery and seasonally-dry forests. We use genomic, phenotypic and habitat heterogeneity data coupled with climatic niche modelling. Results suggest the evolutionary history of the species is mainly related to paleoclimatic changes, although changes in the strength of the Amazon river as a barrier to dispersal, current habitat heterogeneity and geographic distance were also relevant. We propose an ancestral distribution in the Guyana Shield, and recent colonization of areas south of the Amazon river at ~380 to 166 kya, and expansion of the distribution to southern Amazonia, Cerrado and the Atlantic Forest. Since then, populations south of the Amazon River have been subjected to cycles of isolation and possibly secondary contact due to climatic changes that affected habitat heterogeneity and population connectivity. Most Amazonian rivers are not associated with long lasting isolation of populations, but some might act as secondary barriers, susceptible to crossing under specific climatic conditions. Morphological variation, while stable in some parts of the distribution, is not a reliable indicator of genetic structure or phylogenetic relationships.

Taxonomic revision of Saffron-billed Sparrow Arremon flavirostris Swainson, 1838 (Aves: Passerellidae) with comments on its holotype and type locality.

The Saffron-billed Sparrow (Arremon flavirostris) complex occurs in the undergrowth of deciduous woodlands and forests from the Andes of Bolivia and northern Argentina to Paraguay and southern, mid-western and interior eastern Brazil. Currently four subspecies are recognized: A. f. flavirostris, A. f. polionotus, A. f. devillii and A. f. dorbignii. We review the taxonomy of this complex by analyzing coloration and morphometrics of a series of 234 skins, and by comparing 101 sound recordings. Our results suggest that under both the Phylogenetic and Biological Species Concept, three species should be recognized in this complex: A. flavirostris, A. polionotus and A. dorbignii. On the other hand, A. devillii should be considered a junior synonym of A. polionotus since these two have no constant differences in morphology and vocalization. These species are diagnosable by their coloration characters, but not by morphometrics. Vocalizations are useful in diagnosing A. flavirostris from A. dorbignii, but do not diagnose A. polionotus from the others. We show that part of the previous taxonomic confusion can be attributed to variation in back color of adult and immature A. polionotus. Finally, we comment on the recently located holotype of A. flavirostris, which was believed to be lost, and its type locality.