Three new species of Philippine forest mice (Apomys, Muridae, Mammalia), members of a clade endemic to Mindoro Island

Apomys, a Philippine endemic genus of forest mice, occurs throughout most oceanic portions of the archipelago and is its most speciose mammal genus, with 18 species currently recognized. Recent extensive surveys of mammals on Mindoro Island have produced specimens that document the presence of three genetically and morphologically distinct candidate species of Apomys (subgenus Megapomys) previously unknown. These three, plus one previously described relative from Mindoro, constitute a clade of well-supported, reciprocally monophyletic units based on cytochrome b sequence data, all of which are strongly supported using BPP species delimitation. Data from three nuclear genes show less divergence, but species delimitation analyses are consistent with results from cytochrome b. These four taxa are easily diagnosed on the basis of pelage and cranial morphology. Each of the four species occurs allopatrically, though two occur along a single elevational gradient. In this paper, we formally describe the three new species. We estimate that the common ancestor of the four species arrived on Mindoro from Luzon roughly 4.7 Ma, with initial diversification beginning roughly 2.7 Ma, and increasing to the current four species about 1.3 Ma. The three new species increase the number of mammals currently recognized as endemics on Mindoro from nine to twelve. This is a remarkably high number of endemic mammals from an island of its size, and reflects Mindoros status as a geologically old island permanently isolated from other oceanic islands in the Philippines by deep water, while also corroborating Mindoro as the smallest island within which endemic speciation by small mammals is known to have occurred.