Ecological features of an overwintering population of the hillock mouse (Mus hortulanus Nordm.) in the south-west of the U.S.S.R.

Abstract

In this paper, we present data on murid rodents obtained by three major techniques used in biochemical systematics today: protein electrophoresis, scnDNA hybridization and mtDNA RFLP. The data have been analysed by both phenetic and cladistic methods and results of the three techniques were compared with one another. Four clear major levels of divergence (or nodes) can be recognized by all methods. Node 1 groups four subspecies of M. musculus (domesticus, bactrianus, castaneus and musculus). Node 2 groups four species: M. musculus, M. spretus, M. spicilegus and M. spretoides. Node 3 groups the stem of node 2 and three strictly Oriental species (M.caroli, M. ceruicolor and M. cookii) Node 4 groups the previous lineages with Oriental Pyromys and Coelomys and the Ethiopian Nannomys. However, the relationships within each level cannot be resolved without ambiguity. We argue that this is not due to the resolutive power of our methods, but to a biological reality, that is successive adaptive radiations marked by quasi-simultaneous speciation events linked with geographical colonization. Our estimation of divergence time between different taxa showed that the genus Mus is very young. The youngest 'bona fide' species are 1.1 Myr old, or even less than 0.3 Myr if one takes into consideration the two sibling species M. spicilegus and M. spretoides. It appears that mtDNA evolves three to six times faster than scnDNA. The zoogeographical history of the genus can he reconstructed as a series of adaptative radiations leading to the present day distribution of the Palaearctic, Oriental, and Ethiopian groups of taxa.