Evolutionary systematics and biogeography of endemic gerbils (Rodentia, Muridae) from Morocco: an integrative approach

Gerbils of the genus Gerbillus represent an important part of small mammal diversity in arid regions of North Africa, but their taxonomy and evolutionary systematics and biogeography are still poorly known. Based on the recent collection of a series of gerbils in southern Morocco, including at the type localities of three endemic species, we gathered morphological, chromosomal and molecular data on a number of specimens that we compared with other available results. These data provide new insights into the geographical distribution of the endemic species known to date and suggest that an additional and previously undetected species may exist within this area. Multivariate analyses of morphometrical skull data validated the criteria used in the description of some of these species, while confirming the morphological similarity of a set of medium to large-sized species with hairy feet that can be considered sibling species. Karyotypes were useful for the specific assignation of a number of specimens. Molecular phylogenetics and divergence time estimates allow us to draw the first picture of the evolutionary relationships between endemic Gerbillus species from Morocco and related species of North Africa, and to estimate their respective timing of diversification. Most of the lineage emergence events took place during the Pleistocene, a period characterised by a global aridification of North Africa, but more importantly by important climatic and eustatic variations that may have played a role in species differentiation and subsequent expansion. This integrative approach proved to be essential in such species group including morphologically similar species. It also enables to propose testable hypotheses as to possible scenarios of emergence and evolution of these species along the western margin of the Sahara desert.