Secondary contact between species often results in the formation of a hybrid zone, with the eventual fates of the hybridizing species dependent on evolutionary and ecological forces. We examine this process in the Amazon Basin by conducting the first genomic and phenotypic characterization of the hybrid zone formed after secondary contact between two obligate army-antfollowers: the White-breasted Antbird (Rhegmatorhina hoffmannsi) and the Harlequin Antbird (Rhegmatorhina berlepschi). We found a major geographic displacement (∼120 km) between the mitochondrial and nuclear clines, and we explore potential hypotheses for the displacement, including sampling error, genetic drift, and asymmetric cytonuclear incompatibilities. We cannot exclude roles for sampling error and genetic drift in contributing to the discordance; however, the data suggest expansion and unidirectional introgression of hoffmannsi into the distribution of berlepschi.

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Piculus chrysochloros (Vieillot 1818) is a species of woodpecker that ranges from Argentina to Panama, occurring in lowland forests as well as Cerrado, Caatinga and Chaco vegetation. Currently, nine subspecies are accepted, but no study has evaluated individual variation within populations, so the status of these taxa remains uncertain. Here we review the taxonomy and distribution of this species, based on morphological and morphometric data from 267 specimens deposited in ornithological collections. Our results suggest the existence of six unambiguous taxonomic units that can be treated as phylogenetic species: Piculus xanthochloros (Sclater & Salvin 1875), from northwestern South America; Piculus capistratus (Malherbe 1862), from northern Amazonia west to the Branco River; Piculus laemostictus Todd 1937, from southern Amazonia; Piculus chrysochloros (Vieillot 1818), from the Cerrado, Caatinga and Chaco; Piculus paraensis (Snethlage 1907) from the Belém Center of Endemism; and Piculus polyzonus (Valenciennes 1826) from the Atlantic Forest. Both Brazilian endemics (P. polyzonus and P. paraensis) are threatened due to habitat loss. In addition, we found one undescribed form from the Tapajós-Tocantins interfluve, now under study, that may prove to be a valid species once more specimens and other data become available.

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Large Amazonian rivers impede dispersal for many species, but lowland river networks frequently rearrange, thereby altering the location and effectiveness of river barriers through time. These rearrangements may promote biotic diversification by facilitating episodic allopatry and secondary contact among populations. We sequenced genome-wide markers to evaluate the histories of divergence and introgression in six Amazonian avian species complexes. We first tested the assumption that rivers are barriers for these taxa and found that even relatively small rivers facilitate divergence. We then tested whether species diverged with gene flow and recovered reticulate histories for all species, including one potential case of hybrid speciation. Our results support the hypothesis that river rearrangements promote speciation and reveal that many rainforest taxa are micro-endemic, unrecognized, and thus threatened with imminent extinction. We propose that Amazonian hyper-diversity originates partly from fine-scale barrier displacement processes—including river dynamics—which allow small populations to differentiate and disperse into secondary contact.

Abstract:The Estação Ecológica Serra Geral do Tocantins is one of the largest conservation units in Cerrado Biome. The avifauna of this locality was studied from January 25 to 15 February, 2008. We attempted to sample the different habitats found both within the EESGT as in its surroundings. In addition to audio and visual records, mist nets and shotguns were used to collect testimony material, which was deposited in the ornithological collection of the Museu de Zoologia da Universidade de São Paulo (MZUSP). The results were compared with data available from other conservation units nearby the EESGT. We recorded 254 bird species; among these 11 were considered endemic to the Cerrado region and other three considered threatened (Taoniscus nanus, Anodorhynchus hyacinthinus and Procnias averano). Three individuals belonging to the Picumnus genus also were collected; they presented unusual plumage and vocalization patterns, which suggests an undescribed taxon.