Abstract Population divergence and speciation in birds and mammals is often assumed to require an allopatric phase. However, several studies provide evidence that natural selection is the primary driver of diversification, regardless of the geographic context (i.e. divergence-with-gene-flow). In South America, the Chaco-Andes dry forests belt spans a broad environmental gradient, providing opportunity for divergence and local adaptation. We assessed divergence-with-gene-flow in population evolution in a dry forest bird, the Stripe-crowned Spinetail Cranioleuca pyrrhophia (Vieillot, 1818) (Aves, Furnariidae). We studied reduced representation genomic loci, and plumage and body size traits, tested the association of genomic and phenotypic features with geographic and environmental factors, and compared phenotypic with genomic variation (i.e. S-test and PST–FST comparisons). Geographic isolation and elevation predicted phenotypic and genomic variation, with a minor unique impact of climate. These metrics better predicted plumage than body size traits. Certain phenotypic traits exceeded neutral variation, supporting divergent natural selection, with plumage traits being the most differentiated. Plumage traits of this species diverged more rapidly or under stronger selection than other phenotypic traits. This study provides new evidence for the role of divergence-with-gene-flow in shaping phenotypic evolution along environmental gradients. Este resumen traducido al español está disponible en la sección Supporting Information.
Rodríguez–Cajarville et al. (Sat,) studied this question.
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