Molecular phylogeny and biogeography of Madagascar's native rodents (Muridae: Nesomyinae).

Abstract

The nine genera and 21 species of Madagascar's native rodents (Muridae: Nesomyinae) are exceedingly diverse; the only character serving to unite the group is their common distribution on Madagascar. Whether the diversity of nesomyine rodents is the result of a single colonization and subsequent radiation or of multiple independent migrations to the island is controversial. I used complete nucleotide sequences from the mitochondrial cytochrome b gene (1143 bp) as evidence in a phylogenetic analysis to investigate the colonization history for these rodents. All nine nesomyine genera, including multiple individuals from 15 of the 21 species were included in the analysis. Their monophyly was assessed relative to African and Asian murid subfamilies. Cladistic analysis weakly disputes the monophyly of Nesomyinae and suggests that Malagasy rodents form a clade with Steatomys (Dendromurinae) and the African rhizomyine Tachyoryctes. Close association of nesomyines with Mystromys is not supported; rather, Mystromys is the sister taxon to Petromyscus. The resulting phylogeny suggests: (1) nesomyine rodents invaded Madagascar only once, (2) they came from Asia, (3) there was a secondary invasion of rodents from Madagascar into Africa. I also investigated the patterns of speciation and population subdivision of nesomyines within Madagascar. Two types of climatically induced habitat vicariance have been suggested: (1) a shift from mesic to arid climates that cause isolation of humid forest oases in western Madagascar; (2) a shift from cold to warm climate that caused isolation of montane habitats in the eastern highlands. Two disjoint clades of nesomyines show patterns of speciation and population subdivision consistent with these proposed climatic shifts. The current data suggest that nesomyine diversity resulted from an insular radiation, and that their diversification is due in part to habitat vicariance caused by global climatic cycles. Strong tests of nesomyine monophyly will be accomplished with additional character data; I therefore explore the utility of a nuclear gene, the sperm recognition factor Zp-3, for phylogenetic work. I examine the evolution of Zp-3 in the murine genus Mus, identify regions of possible functional significance, and show that the gene provides phylogenetic signal that is congruent with five additional genes for these taxa.