Molecular phylogenetics of the genus Gerbillus (Rodentia, Gerbillinae): Implications for systematics, taxonomy and chromosomal evolution.

Although gerbils forms an important component of the mammalian fauna of arid and semi-arid area, the taxonomic and phylogenetic relationship within the species of the genus Gerbillus are still ambiguous. The present paper introduces findings based on the whole cytochrome b (1140 bp) mitochondrial genes of seven species (Gerbillus campestris, G. latastei, G. nanus, G. tarabuli, G. gerbillus, G. simoni and G. nigeriae) six of which are present in Tunisia. Our results show that all the Gerbillus species are monophyletic. Moreover, molecular phylogeny rejects the genus rank for the taxon Dipodillus. Gebillus nanus, a species belonging to the subgenus Hendecapleura, early diverged from the other species which are divided into two clades: the subgenus Dipodillus, including G. campestris and G. simoni and the subgenus Gerbillus including G. gerbillus, G. nigeriae, G. tarabuli and G. latastei. These results are congruent with morphological and karyological evidences. According to molecular clock, the appearance of the genus Gerbillus coincides with the Miocene-Pliocene expansion of African arid biomes. Extensive intraspecific chromosomal changes evolved in a relatively narrow lapse of time, like in the case of G. latastei, allowing the fixations of different chromosomal variants due to pericentric inversion.

Morphometric analysis of six Gerbillus species (Rodentia, Gerbillinae) from Tunisia.

Size and shape changes in the skull of the genus Gerbillus were investigated using geometric morphometrics. Six species from Tunisia were studied (G. gerbillus, G. campestris, G. nanus, G. tarabuli, G. simoni and G. latastei). Statistical analyses of shape variability allowed us to discriminate three morphological groups which are congruent with the three groups suggested by previous morphological and molecular studies. However, our results contrast with previous molecular investigations. In fact, according to results obtained by the use of principal component analysis, canonical variate analysis and UPGMA, we found a higher degree of divergence between the subgenus Dipodillus and the other two subgenera Gerbillus and Hendecapleura. This fact suggests that the morphometric differences observed among species within the genus Gerbillus are not mainly related to phylogeny. To reconciliate the molecular and morphological approaches, we propose a hypothesis of differential rates of phenotypic evolution in the genus Gerbillus. In this view, the species belonging to the subgenus Dipodillus evolved apomorphic features of the skull likely related to a higher degree of habitat specialization. By contrast, the more generalist Gerbillus and Hendecapleura subgenera show less differentiated plesiomorphic morphology.