Tempo of genetic diversification in southern African rodents: The role of Plio-Pleistocene climatic oscillations as drivers for speciation

The evolution of the southern African faunal assemblages is thought to have been largely influenced by climatic oscillations of the Plio-Pleistocene. These fluctuations presumably had a major impact in the form of vicariant diversification of taxa by causing simultaneous speciation/cladogenetic events due to habitat fragmentation. We aimed to test this hypothesis by comparing the timing of diversification observed for several rodent lineages with three peaks of aridification described at approximately 2.8, 1.7 and 1.0 Mya. Our study included nine rodent taxa (Nannomys, Aethomys, Otomys, Myotomys, Rhabdomys and Mastomys for the Muridae, Saccostomus for the Nesomyidae, Cryptomys for the Bathyergidae, and Xerus for the Sciuridae) that showed intrageneric mitochondrial cytochrome b cladogenesis during the last 5 Ma. Phylogenetic analysis performed with maximum likelihood and Bayesian methods supported the monophyly of all subgenera and genera. Most diversifications are also well supported and in agreement with previously published studies. Divergence dates between lineages were estimated using a Bayesian relaxed molecular clock and the 7 Myr split between different Apodemus species as well as the divergence between Tatera and Gerbillurus at 6.3 Myr were used as calibration points. Our results did not provide any convincing evidence of a correspondence between rodent diversification events and peaks in aridity during the Plio-Pleistocene. The nearly perfect linear correlation between cladogenesis and time, during the last 5 Myr, strongly suggests that the diversification of southern African rodent lineages is driven by complex interactions between different factors, including life history, climatic changes, and topographic barriers.