Résumé
We investigated the phylogenetic position the Ohiya rat, endemic to Sri Lanka, Srilankamys (Rodentia, Murinae), within the tribe Rattini based on the combined analysis of three independent genes (a mitochondrial one and two nuclear exons). Three major lineages (the Maxomys, the Dacnomys and the Rattus divisions) were retrieved as monophyletic groups within the tribe Rattini. Srilankamys was not affiliated to any of the representatives of the Dacnomys division as it was supposed based on morphological characters, but clearly appeared as the first genus to diverge among the Rattus division. The Mindanao Shrew Mouse, Crunomys melanius, emerged as a part of the Maxomys division raising questions about the validity of the Crunomys and the Maxomys divisions as currently defined. Molecular date of divergence between Srilankamys and the other representatives of the Rattus division falls within the interval 6.7 +/- 0.74 Mya, coinciding with the time of the isolation of Sri Lanka from the Deccan peninsula and the aridification period owing to the climate change at the end of the Miocene epoch. We suggest that the isolation of Sri Lanka from the continent, reinforced by the action of a seasonal monsoon-dominated climate, would have led to the isolation of some ancestral rodents of the Rattus division, which would have differentiated later into the Ohiya rat by a vicariant process. In a more general point of view, our study supports the previous results obtained on other organisms and evidence that Sri Lanka appears to be characterized by a particular fauna as compared to the Indian mainland. This island would therefore be considered as a specific distinct hotspot of biodiversity.