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Journal of Biogeography (J. Biogeogr.) (2007) 34, 339–355

Mandibles and molars of the wood
ORIGINAL
ARTICLE mouse, Apodemus sylvaticus (L.):

integrated latitudinal pattern and mosaic
insular evolution

1
Sabrina Renaud * and Johan R. Michaux 2,3

1 Pale ´oenvironnements et Pale ´obiosphe `re, UMR ABSTRACT
5125 CNRS - Universite ´ Lyon 1, Campus de la
Aim The distinct nature of island populations has traditionally been attributed
2
Doua, 69622 Villeurbanne, France, Unite ´ de
either to adaptation to particular insular conditions or to random genetic effects.
Recherches en Zooge ´ographie, Institut de
In order to assess the relative importance of these two disparate processes, insular
Zoologie, Quai Van Beneden 22, 4020 Lie `ge,
3
Belgique and Centre de Biologie et de Gestion effects were addressed in the European wood mouse, Apodemus sylvaticus
des Populations (CBGP), UMR 1062, Campus (Linnaeus, 1758).
International de Baillarguet, CS 30016, 34988,
Location Wood mice from 33 localities on both mainland and various Atlantic
Montferrier/Lez (Montpellier) Cedex, France
and western Mediterranean islands were considered. This sampling covers only
part of the latitudinal range of A. sylvaticus but included the two main genetic
clades identified by previous studies. Islands encompass a range of geographical
conditions (e.g. small islands fringing the continent through large and isolated
ones).
Methods The insular syndrome primarily invokes variations in body size, but
ecological factors such as release from competition, niche widening and food
availability should also influence other characters related to diet. In the present
study, the morphology of the wood mice was quantified based on two characters
involved in feeding: the size and shape of the mandibles and first upper molars.
The size of the mandible is also a proxy for the body size of the animal. Patterns
of morphological differentiation of both features were estimated using two-
dimensional outline analysis based on Fourier methods.
Results Significant differences between mainland and island populations were
observed in most cases for both the mandibles and molars. However, molars and
mandibles displayed divergent patterns. Mandible shape diverged mostly on
islands of intermediate remoteness and competition levels, whereas molars
exhibited the greatest shape differentiation on small islands, such as Port-Cros
and Porquerolles. A mosaic pattern was also displayed for size. Body and
mandible size increased on Ibiza, but molar size remained similar to mainland
populations. Mosaic patterns were, however, not apparent in the mainland
populations. Congruent latitudinal variations were evident for the size and shape
of both mandibles and molars.

Main conclusions Mosaic evolution appears to characterize insular divergence.
The molar seems to be more prone to change with reduced population size on
small islands, whereas the mandible could be more sensitive to peculiar
environmental conditions on large and remote islands.
*Correspondence: Sabrina Renaud, UMR 5125
CNRS – Universite ´ Lyon 1, Ba ˆt. Ge ´ode, 2 rue Keywords
Dubois, Campus de la Doua, F-69622
Apodemus sylvaticus, body size, dentition, Fourier analysis, island syndrome,
Villeurbanne Cedex, France.
E-mail: sabrina.renaud@univ-lyon1.fr mandible shape, morphometrics, Rodentia.

ª 2006 The Authors www.blackwellpublishing.com/jbi 339
Journal compilation ª 2006 Blackwell Publishing Ltd doi:10.1111/j.1365-2699.2006.01597.x