Complete nucleotide sequences from the mitochondrial cytochrome b gene (1143 bp) were used to investigate the phylogenetic relationships among the native rodents of Madagascar. Specifically, this study examines whether the nine genera of nesomyines form a monophyletic group relative to other Old World murids. All nine of the nesomyine genera, including multiple individuals from 15 of the 21 described species, were included in the analysis, and their monophyly was assessed relative to the murid subfamilies Mystromyinae, Petromyscinae, Dendromurinae, Cricetomyinae, Murinae, Rhizomyinae, and Calomyscinae. Phylogenetic analysis of the resulting 95 taxa and 540 characters resulted in 502 equally parsimonious cladograms. The strict consensus tree weakly refutes the monophyly of Nesomyinae and suggests that the Malagasy rodents form a clade with dendromurines (as represented by Steatomys) and the African rhizomyine Tachyoryctes. The cladogram strongly refutes the association of the South African genus Mystromys with the Malagasy genera and suggests that Petromyscus and Mystromys form a monophyletic group. We provide the first explicitly phylogenetic scenario for the biogeographic history of nesomyine rodents. Our phylogenetic hypothesis indicates: (1) rodents invaded Madagascar only once, (2) they came from Asia not from Africa as is commonly assumed, and (3) there was a secondary invasion of rodents from Madagascar into Africa.
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S.A.J. gratefully acknowledges Michael Carleton for illuminating discussions of muroid systematics, Michael Sorenson for expert technical assistance, and Philip Myers for unsel®shly providing computing resources. S.M.G.'s ®eld workÃ in Madagascar was facilitated by the Direction des EauxÂetÂ Forets, l'Association Nationale pour la Gestion des Aires Protegees, and World Wildlife Fund for Nature. Additional tissue samples were generously donated by the Field Museum, the Smithsonian Institution, the Museum at Texas Tech, the Royal Ontario Museum, and Peter Taylor at the Durban Museum. Phil Myers, Michael Carleton, Arnold Kluge, Jennifer Ast, Laura Howard, and Mark Siddall provided helpful comments on earlier drafts. Laboratory work was supported in part by NSF DEB-9209950 to P.K.T. and by Dissertation Improvment Grant DEB-9623426, and grants from the Museum of Zoology, Department of Biology, and the Rackham School of Graduate Studies, University of Michigan, and the American Society of Mammalogists to S.A.J.