Study system
Psammodromus algirus (Linneus, 1758) is the most abundant
lacertid lizard in the Mediterranean scrubland and forest habitats of
the Iberian Peninsula (it is only absent from the northern Eurosiberian
area). It is a medium sized species (snout-vent length: 60-90 mm; body
mass: 6-16 g) in which variation in body size is an important indicator
of fitness, as it determines survival, male attractiveness, and female
fecundity (Díaz 1993, Díaz et al. 2005, Martı́n and Forsman 1997, Iraeta
et al. 2013). P. algirus males present a reddish nuptial
coloration during the months of highest activity (April-June) that can
range from small sublabial marks in subdominant males to occupy
practically the entire head in the largest males. This visual signaling
is complemented by the existence of femoral pores as a means of chemical
signaling. The number of femoral pores is higher in males and their
activity increases as the breeding season advances in response to
increased blood androgen levels (Chiu and Maderson 1975, Cole 1966, Diaz
et al. 1994).
The populations in this study are separated by an altitudinal gradient
of 600-700 m and differ in mean annual temperature, precipitation and
habitat structure. Previous studies on these populations revealed very
little genetic differentiation inferred with mitochondrial DNA
(Verdú-Ricoy et al. 2010), despite the fact that a wide number of
adaptive phenotypic variables are markedly different (Table 1).
The montane population is located at Navacerrada (Cerro de la
Golondrina, Sierra de Guadarrama: 40°44′N, 4°00′W; 1300 m a.s.l.) and
its habitat is composed by deciduos oak forests (Quercus
pirenaica ), scrub patches where Cistus laurifolius predominates
and, to a lesser extent, granite outcrops and grasslands. The average
annual temperature is 6.2 ºC and the average annual rainfall is 1170 mm.
The lowland population is located at El Pardo (Madrid: 40°31′N, 03°47′W;
650 m a.s.l.), a forest of evergreen holm oaks (Quercus ilex )
with shrubs of Cistus ladanifer . It is separated from the montane
population by 32 km in a straight line, and has an average annual
temperature of 12.5 ºC and an average annual rainfall of 438 mm.P. algirus is the most abundant lizard species in both
populations, but reaches higher densities at higher altitude (Díaz
1997).