The bushlike radiation of muroid rodents is exemplified by the molecular phylogeny of the LCAT nuclear gene

Phylogenetic relationships among 40 extant species of rodents, with an emph asis on the taxonomic sampling of Muridae and Dipodidae, were studied using sequences of the nuclear protein-coding gene LCAT (lecithin cholesterol ac yl transferase). Analysis of 804 bp from the exonic regions of LCAT confirm ed many traditional groupings in and around Muridae. A strong support was f ound for the families Muridae (represented by 29 species) and Dipodidae (5 species). Compared with Sciuridae, Gliridae, and Caviomorpha, the Dipodidae family appeared the closest relative of Muridae, confirming the suprafamil ial Myodonta concept. Within the speciose family Muridae, the first branchi ng leads to the fossorial Spalacinae and semifossorial Rhyzomyinae. The rem aining components of Muridae appear as a polytomy from which are issued Sig modontinae, Calomyscinae, Arvicolinae, Cricetinae, Mystromyinae, Nesomyinae , and some Dendromurinae (Steatomys and Dendromus). This phylogeny is inter preted as the result of a bushlike radiation at the end of the early Miocen e, leading to emergence of most living subfamilies. The separation between three additional taxa, Murinae, Gerbillinae, and "Acomyinae" (which compris es the genera Acomys, Deomys, Uranomys, and Lophuromys), has occurred more recently from a common ancestor issued from the main basal radiation. As pr eviously shown by other molecular studies, the vlei rats, Otomyinae, are ne sted within Old World Murinae. In the same way, the zokors, Myospalacinae, appear strongly nested within the hamsters, Cricetinae. Finally, we propose a sister group relationship between Malagasy Nesomyinae and south African Mystromyinae. (C) 2000 Academic Press.