Biogeography and taxonomy of Apodemus sylvaticus (the woodmouse) in the Tyrrhenian region: enzymatic variations and mitochondrial DNA restriction pattern analysis.

In the western Mediterranean area, the taxonomic status of the various forms of Apodemus sylvaticus is quite unclear. Moreover, though anthropogenic, the origins of the island populations remain unknown in geographical terms. In order to examine the level of genetic relatedness of insular and continental woodmice, 258 animals were caught in 24 localities distributed in Belgium, France, mainland Italy, Sardinia, Corsica and Elba. Electrophoresis of 33 allozymes and mtDNA restriction fragments were performed and a UPGMA dendrogram built from the indices of genetic divergence. The dendrogram based on restriction patterns shows two main groups: 'Tyrrhenian', comprising all the Italian and Corsican animals and 'North-western', corresponding to all the other mice trapped from the Pyrenees to Belgium. Since all the Tyrrhenian mice are similar and well isolated from their relatives living on the western edge of the Alpine chain, they must share a common origin. The insular populations are consequently derived from peninsular Italian ones. From a taxonomic point of view and taking the priority rules into account, we have to invalidate A. s. clanceyi Harrison, 1948 and to consider the Tyrrhenian woodmice as belonging to A. s. milleri de Beaux, 1926, whereas the North-western ones must be referred to as the nominal supspecies. As far as the Elban woodmouse is concerned, at the moment we prefer to keep its present subspecific status because we only studied one animal.