Was the exposed continental shelf a long-distance colonization route in the ice age? The Southeast Asia origin of Hainan and Taiwan partridges

- Phylogenetic analyses of insular Hainan and Taiwan partridges and surrounding mainland counterparts.
- Results indicated insular hill partridges originate from non-adjacent Indochina.
- Most studies suggested the biota of these Continental Islands originate from adjacent southeast China mainland.
- Divergence time estimates showed their ancestors reached these islands during glacial periods.
- Probably using the exposed continental shelf along the East Asian coast.

Research on island biotas has greatly contributed to the development of modern evolutionary and biogeographic theories. Until now, most studies have suggested that continental islands received their biotas directly from the adjacent mainland. However, only a few studies have indicated that species on continental islands might originate from other distantly non-adjacent regions. Here, we used the hill partridges (genus Arborophila) that are widely distributed in the southwest and southeast China mainland, Indochina, Hainan and Taiwan islands to test whether species on continental islands might originate from distant regions rather than the adjacent mainland. Based on molecular phylogenies inferred from three mitochondrial fragments and three nuclear introns, together with ancestral area reconstruction, we found that the ancestors of the endemic Hainan and Taiwan partridges (A. ardens and A. crudigularis) likely originated from Indochina, rather than the nearby southeast China mainland. The divergence time estimates demonstrate that their ancestors likely colonized Hainan and Taiwan islands using the long exposed continental shelf between Indochina, Hainan and Taiwan islands during glacial periods, which had not been demonstrated before. Thus, integrating distribution data with phylogenetic information can shed new lights on the historical biogeography of continental islands and surrounding mainland regions.