Genomic architecture drives population structuring in Amazonian birds

Large rivers are ubiquitously invoked to explain the distributional limits and speciation of the Amazon Basin’s mega-diversity. However, inferences on the spatial and temporal origins of Amazonian species have narrowly focused on evolutionary neutral models, ignoring the potential role of natural selection and intrinsic genomic processes known to produce heterogeneity in differentiation across the genome. To test how genomic architecture impacts our ability to reconstruct patterns of spatial diversification across multiple taxa, we sequenced whole genomes for populations of bird species that co-occur in southeastern Amazonian. We found that phylogenetic relationships within species and demographic parameters varied across the genome in predictable ways. Genetic diversity was positively associated with recombination rate and negatively associated with the species tree topology weight. Gene flow was less pervasive in regions of low recombination, making these windows more likely to retain patterns of population structuring that matched the species tree. We further found that approximately a third of the genome showed evidence of selective sweeps and linked selection skewing genome-wide estimates of effective population sizes and gene flow between populations towards lower values. In sum, we showed that the effects of intrinsic genomic characteristics and selection can be disentangled from the neutral processes to elucidate how speciation hypotheses and biogeographic patterns are sensitive to genomic architecture. ### Competing Interest Statement The authors have declared no competing interest.