Climate niche differentiation between two passerines despite ongoing gene flow

Niche evolution underpins the generation and maintenance of biological diversity, but niche conservatism, in which niches remain little changed over time in closely related taxa and the role of ecology in niche evolution are continually debated. To test whether climate niches are conserved in two closely related passerines in East Asia – the vinous-throated (Paradoxornis webbianus) and ashy-throated (P. alphonsianus) parrotbills – we established their potential allopatric and sympatric regions using ecological niche models and compared differences in their climate niches using niche overlap indices in background tests and multivariate statistical analyses. We also used polymorphism data on 44 nuclear genes to infer their divergence demography. We found that these two parrotbills occupy different climate niches, in both their allopatric and potential sympatric regions. Because the potential sympatric region is the area predicted to be suitable for both parrotbills based on the ecological...