A MOLECULAR PERSPECTIVE ON THE SYSTEMATICS AND EVOLUTION OF THE GENUSARVICANTHIS (RODENTIA, MURIDAE) - INFERENCES FROM COMPLETE CYTOCHROME-B GENE-SEQUENCES

Systematics of the genus Arvicanthis, the African unstriped grass rat, are somewhat controversial. Most recent taxonomic revisions List five to six species but the definition of some of these (Arvicanthis dembe ensis, Arvicanthis nairobae, and Arvicanthis niloticus) is uncertain. The complete mitochondrial cytochrome b gene (1140 bp) was sequenced f or 20 specimens from throughout the range of the genus to determine th e intrageneric genetic structure, construct a molecular phylogeny, and evaluate classical taxonomies. Neighbor-joining and maximum parsimony analyses yielded identical phylogenetic trees that identify two major lineages: the first one (1) is composed of specimens usually referred to A. niloticus but representing several distinct species, and the ot her (2) is a complex including ''true'' A. niloticus from Egypt and no rthern West Africa as well as Arvicanthis abyssinicus, Arvicanthis dem beensis, and Arvicanthis somalicus. An analysis on a 357-bp fragment o f the cytochrome b including published data on A. nairobae indicates t hat this taxon is part of clade (1). Calibration of the number of 3rd position transversion changes with the murid fossil record suggests th at clades (1) and (2) diverged approximately 5 Myr ago. Arvicanthis ni loticus as currently recognized is a paraphyletic association and this name should be restricted to the Egyptian and northern West African s ample. We also suggest referring to A. dembeensis as A. niloticus, as our cytochrome b data do not support its recognition as a distinct spe cies. Clade (1) is subdivided in three lineages, geographically corres ponding to southern West, Central, and East Africa. The high genetic d ivergence detected between the Central African lineage and the other t wo lineages suggests that they probably represent separate species. Cl ade (2) experienced rapid cladogenetic events during the late Pliocene , with the A. somalicus lineage being the first to emerge, followed by the ancestor of A. abyssinicus and A. blicki. This period was charact erized by significant climatic and environmental changes, such as the extension of open habitats, which might have provided a stimulus for s peciation in this savanna-dwelling genus. Confrontation of our molecul ar results with chromosomal data shows a high degree of congruence bet ween the two datasets. (C) 1998 Academic Press.