Molecular phylogeny and biogeographic distribution of pheretimoid earthworms (clitellata: Megascolecidae) of the Philippine archipelago

Philippine earthworms are highly diversified both locally and among sites collected on many islands and isolated mountain ranges within large islands. We conducted a molecular phylogenetic and biogeographic analysis of the earthworms from the Philippine islands to provide insight on the species diversification and distribution of these animals in relation to the geological history of the archipelago. The phylogeography of the earthworms was then viewed in light of the geological history of Southeast Asia. The resulting tree shows that the taxonomy of Philippine species of Amynthas, Pithemera, Polypheretima and Pheretima requires revision due to widespread non-monophyly. There appears to have been rapid diversification of Pheretima lineages. Phylogeographical patterns are not clear at the scale of taxon and gene sampling. Each of the four major islands that represented the archipelago during several Pleistocene periods of low sea level shows evidence of multiple colonizations. The lack of clear resolution in our results indicates that the dispersal of earthworms across the islands may have occurred intermittently and from different entry points in the neighboring archipelagoes. The likelihood of dispersal must have dramatically reduced during the times when the sea level rose dividing each of the major islands into several smaller ones. Climate change, the fluctuations in sea level, volcanism, and other ecological factors may have contributed to the rapid diversification of species. Further investigation of the evolutionary history of earthworms in Southeast Asian archipelagoes will require broader geographical sampling, including Indonesia, Malaysia and Australasia.