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).