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.