Molecular phylogenetic approaches have greatly improved our knowledge of the pattern and process of biological diversification across the globe; however, many regions remain poorly documented, even for well-studied vertebrate taxa. The Philippine archipelago, one of the least-studied ‘biodiversity hotspots’ is an ideal natural laboratory for investigating the factors driving diversification in an insular and geologically dynamic setting. We investigated the history and geography of diversification of the Philippine populations of a widespread montane bird, the White-browed Shortwing (Brachypteryx montana). Leveraging dense archipelago-wide sampling, we generated a multi-locus genetic dataset (one nuclear and two mtDNA markers), which we analyzed using phylogenetic, population genetic, and coalescent-based methods. Our results demonstrate that Philippine shortwings (1) likely colonized the Philippines from the Sunda Shelf to Mindanao in the late Miocene or Pliocene, (2) diversified across inter-island barriers into three divergent lineages during the Pliocene and early Pleistocene, (3) have not diversified within the largest island, Luzon, contrary to patterns observed in other montane taxa, and (4) colonized Palawan from the oceanic Philippines rather than from Borneo, challenging the assumption of Palawan functioning exclusively as a biogeographic extension of the Sunda Shelf. Additionally, our finding that divergent (c. 4.0 mya) lineages are coexisting in secondary sympatry on Mindanao without apparent gene flow suggests that the speciation process is likely complete for these shortwing lineages. Overall, these investigations provide insight into how topography and island boundaries influence diversification within remote oceanic archipelagos and echo the results of many other studies in demonstrating that taxonomic diversity continues to be underestimated in the Philippines.
Bibliographical noteFunding Information:
This study was funded by the U.S. National Science Foundation (DEB-0962078 and DEB-1457624 to S.R.) and the Loyola Undergraduate Research Opportunities Program (to M.W. and B.A.). Additional support was provided by a National Science Foundation Major Research Instrumentation award (DBI-0821703) to H.L.M. Field surveys by L.R.H. and colleagues were supported by the Negaunee Foundation and the Brown Fund for Mammal Research and the Ellen Thorne Smith Fund of the Field Museum. For technical assistance in the lab, we thank Sarah Sharief. We are grateful for tissue loans from the University of Kansas, National Museum of the Philippines, and Cincinnati Museum Center. We thank Dave Willard for assistance with tissues at the Field Museum. Sequencing was conducted with assistance from the Field Museum’s Pritzker Lab for Molecular Systematics and Evolution operated with support from the Pritzker Foundation. For helpful feedback on this manuscript, we thank J. Younger and the Bird Division discussion group at the Field Museum. We dedicate this paper to Danilo S. Balete, in recognition of his dedication to studying and conserving Philippine biodiversity through vigorous research and training activities, including superb field surveys that produced most of the specimens on which this project was based.
- Coalescent methods
- Island biogeography
- Molecular dating
- Secondary sympatry
- Southeast Asia