Genomic differentiation with gene flow in a widespread Amazonian floodplain-specialist bird species

Abstract

Aim: Ecological, climatic and palaeogeographical processes drive biological diversification. However, the evolutionary outcomes of those mechanisms are complex and difficult to discriminate. Here, we test how alternative drivers affected connectivity along the Amazonian floodplains generating current patterns of population structure and diversity within the Striped Woodcreeper, a widespread bird species tied to forests seasonally flooded by Amazonian rivers. Location: Amazonian floodplains. Taxon: Xiphorhynchus obsoletus (Aves, Furnariidae). Methods: We sequenced 2213 loci of ultraconserved elements (UCEs) and 20 exons to investigate patterns of genetic structure and connectivity across the Striped Woodcreeper distribution, using a set of spatially explicit methods. Population genetics statistics were calculated for each sampled drainage and within each identified cluster. We tested alternative evolutionary scenarios and estimated past and current demographic parameters implementing a simulation-based framework. Results: Three genetic clusters with high admixture proportions were identified. These clusters are distributed in the western, central and eastern parts of the Amazon Basin and are not correlated with different river water types representing ecological gradients along the floodplains. Instead, migration rates indicate two putative historical barriers along the main channel of the Amazonas-Solimões River. Demographic model tests suggest a process of sequential differentiation, partitioned across the Amazon Basin, with stable population sizes and continuous gene flow. Main conclusion: Our results support the hypothesis that late Quaternary changes in connectivity between the eastern and western Amazonian drainages were responsible for driving genetic differentiation in the Striped Woodcreeper. Genomic differentiation occurred in the presence of long-term gene flow throughout the X. obsoletus distribution, suggesting some degree of continuous historical connectivity across Amazonian floodplains. Compared to previous studies, our results suggest that although connectivity among populations of Amazonian bird species specialized in floodplain habitats varies in response to the same abiotic mechanisms, species-specific differences in habitat use may be a strong predictor of population divergence. © 2021 The Authors. Journal of Biogeography published by John Wiley & Sons Ltd.