Abstract
A phylogeographic study was conducted on the Nile grass rat, Arvicanthis niloticus, a rodent species that is tightly associated with open grasslands from the Sudano-Sahelian regions. Using one mitochondrial (cytochrome b) and one nuclear (intron 7 of Beta Fibrinogen) gene, robust patterns were retrieved that clearly show that (i) the species originated in East Africa concomitantly with expanding grasslands some 2 Ma, and (ii) four parapatric and genetically well-defined lineages differentiated essentially from East to West following Pleistocene bioclimatic cycles. This strongly points towards allopatric genetic divergence within savannah refuges during humid episodes, then dispersal during arid ones; secondary contact zones would have then stabilized around geographic barriers, namely, Niger River and Lake Chad basins. Our results pertinently add to those obtained for several other African rodent as well as non-rodent species that inhabit forests, humid zones, savannahs and deserts, all studies that now allow one to depict a more comprehensive picture of the Pleistocene history of the continent south of the Sahara. In particular, although their precise location remains to be determined, at least three Pleistocene refuges are identified within the West and Central African savannah biome.
Highlights
Current climatic changes and their consequences on the evolution of biodiversity are a hotly debated topic with sometimes highly divergent predictive scenarios [1,2,3,4,5,6]
Within the genus Arvicanthis, two main plurispecific clades emerge: specimens of A. ansorgei, A. cf. rufinus and ANI-2 cytotype form a well-supported monophyletic group (PP of 1.0/bootstrap values (BV) of 93%) whose sister assemblage contains (PP of 1.0/BV of 99%) representatives identified as A. neumanni, A. abyssinicus, A. cf. niloticus and A. niloticus sensu stricto here below referred to as A. niloticus
Within the second main Arvicanthis assemblage, three lineages were clearly retrieved: lineage A (PP of 0.88/BV #50%) is basal and made of two A. cf. niloticus and two A. neumanni specimens from Kenya and Tanzania, respectively; lineage B (PP of 1.0/BV of 100%) is represented by the two A. abyssinicus specimens from Ethiopia; lineage C (PP of 0.71/BV of 84%) groups all A. niloticus specimens (Figure 1)
Summary
Current climatic changes and their consequences on the evolution of biodiversity are a hotly debated topic with sometimes highly divergent predictive scenarios [1,2,3,4,5,6]. Rodents appear as excellent alternative phylogeographic markers owing to their usually strong affinities to particular ecological niches and wide geographic distribution, their short generation time, their weak dispersal abilities as well as their small size that may render them highly sensible to geographic barriers such as mountains or large rivers, limiting admixture between allopatrically differentiated lineages. These characteristics are expected to greatly facilitate detection of phylogeographic patterns. Data are available for rodent species inhabiting arid zones (Jaculus jaculus: [12]), steppes, shrub and tree savannahs (Lemniscomys striatus: [13]; Praomys daltoni: [14]; Mastomys erythroleucus: [15,16]; Mastomys natalensis: [17]), rocky habitats (Acomys chudeaui: [18]), humid areas (Mastomys huberti: [19]), forest-savannah mosaics [Mus (Nannomys) minutoides: [20] and forests (Praomys rostratus and P. tullbergi: [21]; P. misonnei: [22,23])
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