On the mtDNA restriction patterns variation of the Iberian wood mouse (Apodemus sylvaticus). Comparison with other west Mediterranean populations

In previous studies, the presence of three main lineages of wood mice mtDNA was described in western Europe: a first one distributed from the Pyrenees to Scandinavia, a Thyrrenian one occurring in peninsular Italy, Elba, Cors ica and Sardinia and a third one restricted to Sicily and Marettimo. Do the Iberian wood mice belong to one of these lineages? In order to answer this question, animals were trapped all over the Iberian peninsula (11 sites) a s well as in three of the Balearic islands. Comparisons with specimens from the above mentioned lineages were made. From 158 animals trapped in 30 sit es, 78 different mtDNA restriction patterns were obtained and compared usin g the NEI and LI index ((Nei M and Li WH, (1979). Mathematical model For st udying genetic variation in terms of restriction endonucleases. Proc. Natl. Acad. Sci. USA 76: 5269-5273) of nucleotide divergence. A neighbour-joinin g tree, with a specimen of Apodemus flavicollis as outgroup. was then compu ted from the similarity matrix. Apodemus flavicollis is well separated from all the A. sylvaticus and all the Iberian restriction patterns are cluster ed with those of continental France, showing a great similarity level betwe en the Iberian and north-west European animals. This group is well separate d from the Sicilian and from the Tyrrhenian ones. These results suggest tha t the Pyrenees are not a biogeographic barrier for the wood mouse and that the postglacial recolonisation of western Europe by that species has its or igin in populations which, during the latest Ice age. were living in refuge s situated in southern France or in the Iberian peninsula. Because the Bale aric restriction patterns are clustered in a lineage joining Iberian patter ns at a low divergence level, we suggest that their origin is continental S pain or southern France.