Genetic data from the extinct giant rat from Tenerife (Canary Islands)

Evolution of vertebrate endemics in oceanic islands follows a predictable pattern, known as the island rule, according to which gigantism arises in originally small-sized species and dwarfism in large ones. Species of extinct insular giant rodents are known from all over the world. In the Canary Islands, two examples of giant rats, Canariomys bravoi and Canariomys tamarani, endemic to Tenerife and Gran Canaria islands, respectively, disappeared soon after human settlement. The highly derived morphological features of these insular endemic rodents hamper the identification of their mainland relatives and the reconstruction of their evolutionary histories. We have retrieved partial mitochondrial (mtDNA) data from C. bravoi and used this information to explore its evolutionary history. The resulting dated phylogeny confidently places C. bravoi within the African grass rat clade (Arvicanthis niloticus). The estimated divergence time, 650,000 years ago, is roughly coincident with the onset of the Günz-Mindel interglacial stage. C. bravoi ancestors would have reached the island via passive rafting and then underwent a yearly increase of mean body mass calculated between 0.0015 g and 0.0023 g; this corresponds to fast evolutionary rates (in darwins [d], ranging from 7.09 d to 2.78 d) that are well above those observed for non-insular mammals.