Summary 1.In reptiles, growth is subject to proximate environmental influences, such as food availability and temperature, that may be crucial during the early stages of postnatal development. Mediterranean regions, with their severe summer drought, offer an excellent opportunity to examine the effects of environmental variations in precipitation and productivity on the timing of reproduction and growth rates of lizards. 2. In this study, we compared the incubation time, size at hatching, growth rates and changes in juvenile body condition of two nearby populations of the lizard Psammodromus algirus separated by 600-700 m altitude in central Spain. We combined a reciprocal incubation experiment at 27 and 30 ° C with a reciprocal transplant experiment to distinguish between environmental and population-specific sources of geographical variation. 3. At both temperatures, eggs from the high-elevation site hatched sooner. Several important phenotypic traits of juveniles were primarily determined by the growing environment: the high-elevation site provided more food and allowed hatchlings to grow faster and reach larger size. 4. Environmental effects overrode familial ones, as shown by the larger growth rate of half-sibs released at the high-elevation site. However, both the size and the growth rate of juveniles were also influenced by their mother's site of origin, which means that population differences may reflect a genetic differentiation and/or different maternal effects. 5. Low precipitation and associated food scarcity were seemingly the main factors constraining the growth rates of juveniles at the lowland site.

Aim In an effort to disentangle the ecological processes that confine ectotherms to alpine environments, we studied the thermoregulatory and microhabitat selection behaviours of the rock lizard Iberolacerta cyreni, which is endemic to some mountains of central Spain, and of the wall lizard Podarcis muralis, which is a potential competitor of rock lizards.Location We chose three areas in the Sierra de Guadarrama (central Spain) that differed in their thermal quality [mean deviation of environmental operative temperatures from the lizards' preferred thermal range (PTR)] and refuge availability: a pine forest (1770 m a.s.l.) in which P. muralis was the only species found, and two mixed shrub and rock sites (1770 and 1900 m a.s.l.) where both species were present.Methods In the field we collected data on refuge availability, sun exposure, body temperature (T b ) and operative temperature (T e ). Thus, we estimated the thermal habitat quality of the areas sampled and the thermoregulation accuracy and effectiveness of both species. ResultsThe pine forest had the lowest thermal quality and refuge availability. The lower-elevation shrub site offered the best thermal quality, but refuges were much scarcer than at the higher-elevation site. Both species thermoregulated accurately, because mean deviations of body temperature (T b ) from PTR were considerably smaller than those of T e . Podarcis muralis had higher T b values than did I. cyreni, which had similar T b values at both shrub sites, whereas P. muralis had lower T b values at higher elevation. Overall, the thermoregulatory effectiveness (extent to which T b values are closer to the PTR than are T e values) of both species was similar, but whereas I. cyreni thermoregulated more efficiently at higher elevation, the opposite was true for P. muralis. At the lower-elevation shrub site, I. cyreni remained closer to refuges than did P. muralis. Main conclusionsOur results suggest that the pine forest belt might prevent the expansion of rock lizards towards lower elevations as a result of its low thermal quality and scarcity of refuges, that the thermoregulatory effectiveness of rock lizards in alpine environments depends more on refuge availability than on thermal habitat quality, and that competition with wall lizards is unlikely to explain either the distribution or the thermoregulatory effectiveness of rock lizards.

The trade-off between clutch and offspring size, which is a central topic in life-history research, is shaped by natural selection to maximize the number of surviving offspring, but it also depends on the resources available for reproduction. Conspecific populations living in different environments may differ in adult body size, clutch mass, clutch size, offspring size, and/or post-natal growth rates, due either to phenotypic plasticity or to local adaptation. Here, we compare these traits and their relationships between two populations of the lizard Psammodromus algirus separated by a 600-m altitudinal gradient. We used a common garden design to control incubation temperature and food availability, with two different feeding treatments. Females were larger at the high-elevation site. Although SVL-adjusted clutch mass did not differ between populations, high-elevation females laid more but smaller eggs than low-elevation ones. Hatchlings were larger at lower elevation. Our common garden experiment revealed that low-elevation hatchlings grew faster than high-elevation hatchlings under both feeding treatments. However, higher food availability at higher altitude allows high-elevation lizards to grow faster and attain larger adult sizes, especially in the case of females. The two key adaptations of low-elevation lizards, large eggs and hatchlings and the ability to grow rapidly after hatching, are likely to enhance survival in low-productivity Mediterranean lowlands. Our data support the hypothesis that the reproductive strategies of these populations provide an example of countergradient variation, because the genotypes that encode for fast growth and large body size occurred in low food availability habitats where juveniles grew slowly and attained small adult sizes.

Aim We examined dorsal coloration in and genetic relationships among Iberian populations of the lizard Psammodromus algirus to determine the extent to which the current distribution of phenotypic variation is correlated with phylogeographical history or local environmental conditions. Location Iberian Peninsula, western Palaearctic. MethodsWe sequenced mitochondrial DNA (ND4 and adjacent tRNAs genes) in 36 populations, and seven microsatellite loci in eight representative populations. In 23 populations, lizards were classified according to the presence and intensity of a dorsal striped pattern, the heritability of which was estimated by means of mother-offspring regressions. To determine whether colour pattern is an adaptation for crypsis, we compared the time taken by humans to detect striped and unstriped lizards in different environments.Results The analysis of mtDNA revealed an ancient split between a western clade, subdivided into south-and north-western haplogroups, and an eastern clade with central, south-eastern and eastern haplogroups. In contrast, nuclear markers showed a post-glacial admixture of central and western haplogroups, with the central haplogroup apparently isolated from the rest of its clade. This was consistent with variation in the dorsal striped pattern, a heritable phenotypic trait: central and western lizards were unstriped, whereas eastern lizards were striped. We then suggest that dorsal coloration promotes crypsis: in eastern locations detection times were longer for striped than for unstriped lizards, whereas the opposite was true in western and central locations. Main conclusionsOur results indicate that natural selection for crypsis may promote not only divergence within clades, as suggested by the apparent isolation between unstriped central lizards and striped members of eastern haplogroups, but also admixture between them. We conclude that ecologically driven selection is crucial for understanding the phylogeographical background of phenotypic variation, because recent adaptation to the environment can blur the effects of ancestral isolation.

Intraspecific variation in morphology has often been related to fitness differences through its effects on performance. In lizards, variation in hind limb length can be shaped by natural selection for increased locomotor performance, sexual selection on the number or size of femoral pores involved in chemical signalling, or both. Here, we analyse the selective forces involved in sexual dimorphism and differences in hind limb length between two populations of Psammodromus algirus living at different elevation. Males were more robust and had longer hind limbs and limb segments than females, and low-elevation lizards had longer limbs than high-elevation lizards. However, differences in locomotor performance were small and non-significant, making natural selection for faster runs an unlikely explanation for the observed pattern. On the other hand, males had more femoral pores than females, and lizards had more pores at lower elevation, although the difference was significant only for males (which invest more in chemical signalling). In males, the number of pores, which remains constant along a lizard's life, was not correlated with hind limb length. However, femur length was positively correlated with mean pore size, allowing low-elevation males to have larger than expected pores, which could increase the effectiveness with which they spread their signals in a dry and warm habitat where chemicals become volatile rapidly. Also, saturation of the sexual coloration of the head was higher for low-elevation males, suggesting that sexual selection pressures may be more intense. Overall, our results indicate that sexual selection plays a significant role in shaping intraspecific variation in hind limb length.