Dating of divergences within the Rattus genus phylogeny using whole mitochondrial genomes

The timing and order of divergences within the genus Rattus have, to date, been quite speculative. In order to address these important issues we sequenced six new whole mitochondrial genomes from wild-caught specimens from four species, Rattus exulans, Rattus praetor, Rattus rattus and Rattus tanezumi. The only rat whole mitochondrial genomes available previously were all from Rattus norvegicus specimens. Our phylogenetic and dating analyses place the deepest divergence within Rattus at similar to 3.5 million years ago (Mya). This divergence separates the New Guinean endemic X praetor lineage from the Asian lineages. Within the Asian/Island Southeast Asian clade R. norvegicus diverged earliest at similar to 2.9 Mya. R. exulans and the ancestor of the sister species R. rattus and R. tanezumi subsequently diverged at similar to 2.2 Mya, with R. rattus and R. tanezumi separating as recently as similar to 0.4 Mya. Our results give both a better resolved species divergence order and diversification dates within Rattus than previous studies. (C) 2008 Elsevier Inc. All rights reserved.