Although tropical and subtropical Asia harbour a high level of species diversity, their species richness can be underestimated because species which are in fact distinct have not been separately identified. In this study, we delimit Bambusicola thoracica into two full species, the Chinese bamboo partridge (B. thoracica) in continental Asia and the Taiwanese bamboo partridge (B. sonorivox) on the island of Taiwan, using coalescent-based multilocus division and diagnosable vocalization patterns. Isolation-with-migration analysis indicated that the two bamboo partridges diverged approximately 1.8 million years ago, with gene flow present most probably during the early stages of their divergence. This conclusion supports the hypothesis that diverging lowland lineages spread across the Asian mainland, and continental islands have more opportunities for secondary contact than highland ones when the sea level was low. Our results imply that conservation of biodiversity in tropical and subtropical Asia could be hindered by overlooking numerous 'hidden' species and highlight the importance of re-examining the taxonomic statuses of species in this region traditionally defined as polytypic.
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