Review of Moluccan Rattus (Rodentia: Muridae) with Description of Four New Species

Four new species of Rattus are described from the Moluccan islands (Maluku) of Indonesia: Rattus taliabuensis and R. feileri, both from the island of Taliabu, and R. halmaheraensis and R. obiensis from the islands of Halmahera and Obi, respectively. These descriptions are presented as part of a taxonomic review of Moluccan Rattus based on all known specimens in museum collections worldwide. Morphological characters, molecular systematics, and geographical distributions are documented for each of these species. Using both morpho-anatomical and morphometric approaches, we found that the Maluku Islands support Rattus taxa with spiny fur and two distinct morphotypes (1) species with a long tail and short rostrum (R. morotaiensis, R. halmaheraensis, R. obiensis, R. feileri) and (2) species with a short tail and long rostrum (R. taliabuensis, R. feliceus, R. ceramicus, R. elaphinus). Most of the new Moluccan species belong to a clade that includes members of the R. xanthurus species group from Sulawesi and the Australo-Papuan Rattus lineages. Their phylogenetic relationships highlight the role of Wallacea as an important area for diversification of Rattus into the Australo-Papuan region. Finally, the morphologically distinctive taxon Nesoromys ceramicus from Seram was found to be sister species to R. feliceus, and we relegate Nesoromys into the synonymy of the genus Rattus. The close affinities between R. ceramicus and R. feliceus may be an example of in situ island speciation, which has not been observed for small mammals on other Maluku Islands.