Diversity and phylogenetic implications of CsCl profiles from rodent DNAs

Buoyant density profiles of high-molecular-weight DNAs sedimented in CsCl g radients, i.e., compositional distributions of 50- to 100-kb genomic fragme nts, have revealed a clear difference between the murids so far studied and most other mammals, including other rodents. Sequence analyses have reveal ed other, related, compositional differences between murids and nonmurids. In the present study, we obtained CsCl profiles of 17 rodent species repres enting 13 families. The modal buoyant densities obtained for rodents span t he full range of values observed in other eutherians. More remarkably, the skewness (asymmetry, mean - modal buoyant density) of the rodent profiles e xtends to values well below those of other eutherians. Scatterplots of thes e and related CsCl profile parameters show groups of rodent families that a gree largely with established rodent taxonomy, in particular with the monop hyly of the Geomyoidea superfamily and the position of the Dipodidae family within the Myomorpha. In contrast, while confirming and extending previous ly reported differences between the profiles of Myomorpha and those of othe r rodents, the CsCl data question a traditional hypothesis positing Glirida e within Myomorpha, as does the recently sequenced mitochondrial genome of dormouse. Analysis of CsCl profiles is presented here as a rapid, robust me thod for exploring rodent and other vertebrate systematics. (C) 2000 Academ ic Press.