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Hereditas 129 (1998)      mtDNA variabilitv of Iberian wood mouse (Apodemus sylvaticus) 191

  123456                                                        (COOPERet al., 1995) for which the Pyrenees are a
                                                                suture zone between two groups of populations.
                                                4 1650
                                                                  So, the Pyrenees do not constitute a serious obsta-
                                               4 790            cle for the wood mice north-south dispersal move-
                                                                ments. The north-south orientation of the main
                                                 4 366          valleys and the low altitude of many passes between
                                                                the southern and the northern parts of the mountain
                                                 4 267          chain leads to a continuity in the forest cover and
                                                                perhaps favours the wood mouse settlement. More-
Fig. 3. Restriction patterns after &a I endonuclease diges-     over, either near the Atlantic coast or near the Med-
tion of wood mouse mtDNA from 1: Ma1 (pattern SO); 2:           iterranean border, this forest cover is also
Me1 (pattern 79); 3: Ibl (pattern 53); 4: S3 (pattern 63); 5:   uninterrupted between France and Spain due to suffi-
S5 (pattern 29) and 6: I1 (pattern 1). The size scale in BP is  cient rainfalls, to suitable edaphic conditions and to
indicated on the right.                                         the low altitude of the mountains. The situation
                                                                prevailing in the Alps is contrasting, at least in the
DISCUSSION AND CONCLUSIONS                                      western part, because the summit line is higher, the
The mean level of sequence divergence of nucleotides            altitude of only a few passes being just under or near
between Iberian and French animals is quite low and             the tree line. Near the Mediterranean sea, the pied-
therefore Iberian animals can be considered as a part           mont is very dry and the soil is stony, leading to
of the ‘north-western’ group whose distribution area            ecological conditions unsuitable for the wood mouse.
extends to Scandinavia (TEGELSTR~aMnd JAAROLA                   In the past, the ice sheet was more developed in the
1989; VAN ROMPAEY1989; MICHAUXet al. 1996).                     Alps than in the Pyrenees, probably preventing the
These data strongly suggest that the post-glacial re-           northward expansion of the mice populations isolated
colonisation of north-west Europe is the consequence            in the Italian refugium. This Alpine discontinuity has
of the spreading of a clade which found refuge in the           been evidenced in many other species including mam-
Iberian peninsula or in the very southern France                mals (Sorex araneus, Arvicola terrestris: TABERLETet
during the latest Ice age. This colonisation route is           al., 1994; TABERLEeTt al. 1998), amphibians (Tritu-
identical for the wood mouse, the brown bear (Ursus             rus sp.: WALLISand ARNTZEN1989), fish (Salmo
arctos) and some white oaks (Quercus spp.) haplo-               trutta: BERNATCHEeZt al. 1992) or insects (Chorthip-
types (TABERLETet al., 1998) but differs for other              pus parallelus: COOPERet al. 1995; Apis melliJica:
species like the grasshopper Chorthippus parallelus             GARNERYet al. 1992).

                                                                  As far as the divergence level between the Iberian
                                                                samples is very low, it can be assumed that there is no
                                                                evidence for two distinct wood mice groups within
                                                                the Iberian Peninsula. This conclusion is in complete
                                                                accordance with the results of the morphological
                                                                study of RAMALHINHOand MADUREIRA(1982).
                                                                Moreover, a multivariate (PCA, multiple discrimi-
                                                                nant analysis) craniometric study (MICHAUX1996)
                                                                shows that the Iberian wood mice are hardly distin-
                                                                guished from those trapped in France, Belgium and

                                                                   In conclusion, we suggest that the existence of
                                                                Apodemus s. dichrurus in Spain and in southern

Table 2. Woodmouse haplotype diversity in the different regions

                      No. haplotypes  No. animals               Diversity index  Equitability index

Sicily                 5               6 2.252                                   0.969
Italy                 15              33 3.555                                   0.91
France                21              41 4.047                                   0.921
Balearic islands      10              23 3.029                                   0.912
Iberian Peninsula     30              55 4.686                                   0.955

Id. +France           48              96 5.304                                   0.95
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