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Hereditas 129: 187-194 (1998)

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

J. R. MICHAUX', R. LIBOIS', M. G. RAMALHINH02 and C. MAUROIS'

Unit6 de recherches zooggographiques, Institut de Zoologie, Universitk de Li2ge, Lisge, Belgium
Centro de Biologia ambiental da Universidade de Lisboa, Lisboa, Portugal

Michaux, J. R., Libois, R., Ramalhinho, M. G . and Maurois, C. 1998. On the mtDNA restriction patterns variation of the
Iberian wood mouse (Apodemus syluuticus). Comparison with other west Mediterranean populations. -Hereditus 129:
187-194. Lund, Sweden. ISSN 0018-0661. Received April 23, 1998. Accepted November 9, 1998

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, Corsica 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) as well as in three of the
Bdearic islands. Comparisons with specimens from the above mentioned lineages were made. From 158 animals trapped
in 30 sites, 78 different mtDNA restriction patterns were obtained and compared using the NEIand LI index ((Nei M and
Li WH, (1979). Mathematical model for studying genetic variation in terms of restriction endonucleases. Proc. Natl.
Acad. Sci. USA 76: 5269-5273) of nucleotide divergence. A neighbour-joining tree, with a specimen of Apodemus
flavicollis as outgroup, was then computed from the similarity matrix. ApodernusJlauicollis is well separated from all the
A . syluaticus and all the Iberian restriction patterns are clustered with those of continental France, showing a great
similarity level between the Iberian and north-west European animals. This group is well separated from the Sicilian and
from the Tyrrhenian ones. These results suggest that the Pyrenees are not a biogeographic barrier for the wood mouse
and that the postglacial recolonisation of western Europe by that species has its origin in populations which, during the
latest Ice age, were living in refuges situated in southern France or in the Iberian peninsula. Because the Balearic
restriction patterns are clustered in a lineage joining Iberian patterns at a low divergence level, we suggest that their origin
is continental Spain or southern France.

R . Libois, Unite de recherches zoogt!ographiques, Institut de Zoolopie, UnivrrsitP de LiPge, quai Van Beneden, 22, B-4020
Lisge, Belgium. E-mail: Roland.Libois@ulg.ac.be

In a previous study (MICHAUXet al. 1996), two mtDNA lineages, has prevented the Italian animals
lineages of wood mice (Apodemus sylvaticus) mtDNA to move northwards after glaciation. We wonder if
were described in western Europe. The first one the Iberian wood mice are distinct from the north-
(northwestern) extends from the Pyrenean mountains western ones and if the Pyrenees played the same role
to Scandinavia and the second one is distributed all as the Alps at the end of the last glaciation.
over the Italian peninsula and in the Tyrrhenian
islands (Elba, Corsica, Sardinia). A third group is Two distinct subspecies are currently reported in
recognised in Sicily and in Marettimo (MICHAUXet the Iberian peninsula: Apodemus sylvaticus dichrurus
al. 1998). (Rafinesque, 1814) considered as the Mediterranean
subspecies and A . s. callbides (Cabrera, 1907) sup-
Till now, no information about the genetic vari- posed to inhabit the Cantabric and the Pyrenean
ability of the Iberian wood mouse intDNA is chains and even to extend towards the Massif Central
available. (MILLER1912; SAINTGIRONS1966, 1973).

As the wood mouse is mainly a forest dweller In their morphological study of Portuguese speci-
whose altitudinal and latitudinal distribution mens, RAMALHINHaOnd MADUREIRA(1982) did not
boundaries are close to the tree limit, it is conceivable find any crucial difference between the north Por-
that during the latest Ice age, its distribution was tuguese animals thought to belong to callbides and
restricted to the remaining forest areas of southern the south Portuguese ones ascribed to dichrurus. Nev-
Europe e.g. in southern France and in some parts of ertheless, animals are slightly bigger in the south than
the Italian and Iberian peninsulas. in the north. This fact is highlighted by SANS-COMA
et al. (1987) in Spain too. Despite that these morpho-
Consequently, north-west Europe must have been logical differences are slight, the existence of two
reached by wood mice originating from these forest distinct forms of the wood mouse in the Iberian
zones. Certainly, the alpine chain which constitutes peninsula cannot be excluded.
the north-occidental boundary between the two main