Pleistocene glaciation explains the disjunct distribution of the Chestnut-vented Nuthatch (Aves, Sittidae)

Pleistocene climatic oscillations have played an important role in shaping many species' current distributions. In recent years, there has been increasing interest in studying the effects of glacial periods on East Asian birds. Integrated approaches allow us to study past distribution range changes due to Pleistocene glaciation, and how these changes have affected current population genetic structure, especially for species with unusual distribution patterns. The Wuyi disjunction is the disjunct distribution of birds between the Wuyi Mountains in south-eastern China and south-western China. Although several species exhibit the Wuyi disjunction, the process behind this unusual distribution pattern has remained relatively unstudied. Therefore, we used the Chestnut-vented Nuthatch Sitta nagaensis as a model species to investigate the possible causes of the Wuyi disjunction. Based on phylogenetic analyses with three mitochondrial and six nuclear regions, the Wuyi population of the Chestnut-vented Nuthatch was closely related to populations in mid-Sichuan, from which it diverged approximately 0.1 million years ago, despite the long geographical distance between them (over 1,300 km). In contrast, geographically close populations in mid- and southern Sichuan were genetically divergent from each other (more than half a million years). Ecological niche modelling suggested that the Chestnut-vented Nuthatch has experienced dramatic range expansions from Last Interglacial period to Last Glacial Maximum, with some range retraction following the Last Glacial period. We propose that the Wuyi disjunction of the Chestnut-vented Nuthatch was most likely due to recent range expansion from south-western China during the glacial period, followed by postglacial range retraction.