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Introduction

Morphological
variation
is
an
important
aspect
of
biodiversity,
in
particular
because
phenotypic

variation
is
an
important
target
of
the
screening
by
selection.
Its
study
can
bring
light
onto
the

adaptive
component
of
morphological
diversification,
thus
constituting
a
precious
complement
to

the
vastly
and
rapidly
developing
field
of
genetic
and
genomic
analyses.
Furthermore,
morphological

evolution
can
be
studied
on
both
modern
and
fossil
species,
and
can
thus
help
to
bridge
the
gap

between
different
temporal
scales,
from
contemporary
evolution
to
long
term
trends
along
millions

of
years.

Patterns
of
morphological
evolution
have
long
been
studied,
including
for
deciphering
rodent

evolution
(e.g.
Misonne
1969;
Michaux
1971;
Butler
1985).
This
field
of
investigation
has
been

renewed
by
the
development
of
methods
allowing
the
quantification
of
fine-­‐scale
shape
variation,

namely
geometric
morphometrics
(e.g.
Rohlf
and
Marcus
1993;
Bookstein
1991;
Mitteroecker
and

Gunz
2009).
Such
methods,
based
on
landmarks
or
outline
analyses,
have
been
used
to
tackle
many

topics
regarding
rodent
evolution:
evolutionary
patterns
along
fossil
lineages
(Renaud
et
al.
1996,

2005;
Piras
et
al.
2009;
Stoetzel
et
al.
2013),
diversification
among
species,
addressing
the
respective

role
of
adaptation
and
neutral
evolution
(e.g.
Cardini
2003;
Monteiro
et
al.
2005;
Macholan
2006;

Michaux
et
al.
2007a);
differentiation
between
populations,
investigating
the
role
of
environmental

variations
(Renaud
1999;
Fadda
and
Corti
2001;
Renaud
and
Michaux
2003,
2007;
McGuire
2010;

Helvaci
et
al.
2012),
processes
favoring
co-­‐occurrence
among
species
(Ledevin
et
al.
2012),
patterns

and
route
of
colonization
(Valenzuela-­‐Lamas
et
al.
2011;
Siahsarvie
et
al.
2012;
Cucchi
et
al.
2013).

Insular
differentiation
provided
numerous
models
of
pronounced
morphological
differentiation

questioning
the
respective
role
of
adaptation
and
random
factors
(Cardini
et
al.
2007a;
Michaux
et
al.

2007b;
Renaud
and
Michaux
2007;
Renaud
and
Auffray
2010;
Renaud
et
al.
2013).
Even

contemporary
evolution
and
response
to
current
anthropic
changes
can
find
a
morphological

signature
in
rodents
(Pergams
and
Lacy
2008;
Renaud
et
al.
2013).

All
these
studies
rely
on
the
characterization
of
patterns
of
morphological
differentiation.
Advances

in
evolutionary
biology,
quantitative
genetics
(e.g.
Klingenberg
et
al.
2001;
Workman
et
al.
2002)
and

developmental
biology
(e.g.
Kassai
et
al.
2005;
Kavanagh
et
al.
2007;
Prochazka
et
al.
2010)

challenged
to
bridge
the
gap
from
patterns
to
processes
within
an
integrated
‘evo-­‐devo’
framework.

The
analysis
of
morphological
variation
is
of
interest
in
this
context
(Polly
2008;
Renaud
and
Auffray

2013)
because
it
is
the
product
of
the
underlying
genetic
variation
and
developmental
pathways.

Widespread
variants
can
point
to
developmental
mechanisms
favoring
their
production
(e.g.
Renaud

et
al.
2011).
They
will
have
a
higher
chance
of
spreading
within
a
population,
either
by
selection
or
by