The role of repeated sea-level fluctuations in the generation of shrew (Soricidae: Crocidura) diversity in the Philippine Archipelago

Repeated sea-level fluctuations during and prior to the Pleistocene had a dramatic effect on the distribution of land and connection among islands between the Asian and Australian continents. These cycles of connection and isolation have long been recognized as an important factor determining the distribution and organization of biodiversity in the Philippines. However, surprisingly few studies have tested for predicted patterns of genetic diversity derived from a Pleistocene sea-level model of geography. Here, we examine evidence for fit to such a model in a widely distributed lineage of shrews (Crocidura). The topology of relationships among Crocidura from the Philippines is concordant with a Pleistocene sea-level model, but (1) AMOVAs reveal that genetic diversity is explained at least as well by modern islands as by Pleistocene islands; (2) Mantel tests reveal a significant influence of isolation by distance; and (3) the degree of genetic divergence between some populations connected by dry land during the last glacial maximum reveals isolation that almost certainly predates the most recent glacial activity. We further employ multiple strategies for inferring time-calibrated phylogenies, but these result in widely varying time estimates for the invasion of SE Asian islands by shrews. Overall, our results suggest Pleistocene sea-level fluctuations have been an important, but not dominant factor shaping shrew diversity.