Worldwide roads are in continuous expansion, with an expected increase of >60% by 2050. This may increase selection pressures on wildlife, urging applied ecologist to investigate the adaptive potential of populations to forecast long-term effects. Most of the works to date have been individual-focused, obviating the potential evolutionary impact of these infrastructures on populations of small vertebrates with low migration capability (e.g., lizards). Pressure associated to road proximity can be indirectly derived from habitat transformation and degradation. We hypothesize that we can demonstrate the selective effects of a road by comparing lizard phenotypes between subpopulations differing in proximity to the linear infrastructure. Thus, to investigate selective effects as a function of road proximity, we selected two150 meter-wide sampling bands of terrain that were one close to a road and the other one 500 m away from it. We studied differences in vegetation cover, prey availability, abundances of aerial predators and lizards, female phenology, and hatching date as indicators of habitat quality, associated to the presence of the road, and as possible drivers of subsequent differences in the lizard traits between subpopulations. Mean values of head and body size, body condition, ecto- and endoparasite loads, tail state, and male nuptial coloration (all traits associated to individual quality) were compared as base-line indicators of disruptive selection. Near-males had an earlier investment of nuptial coloration in life, but coloration was of poor quality as compared to far-males. Hatching date was earlier in the far subpopulation, and juveniles were bigger prior to hibernation there. In addition, during two years, we carried out a two-step capture-recapture translocation experiment. In the spring of the first year, we individually marked 120 males, 60 per sampling band, and translocated 30 of them from close to the road to far from the road, and vice-versa. The remaining 60 males formed two control groups, close and far from the road, respectively. A balanced subsample of 25% of the males was recaptured ~30 days, in average, after the first capture. Intergroup differences in individual change of body condition, parasite load, and sexual coloration were calculated and used to quantify the response of the lizards to the road proximity. We found an effect of the treatment on
the lizards: translocated lizards lost weight. However, control individuals far from the road significantly increased their body condition compared to the rest of experimental groups. Interestingly, these same lizards reduced their endoparasite load, suggesting a
selective impact of the road because no differences were initially detected in parasite load or body condition between subpopulations. This was confirmed during the spring of the second year when 30% of the lizards, marked the previous year, were recaptured near the road. The variation observed in the traits measured confirmed that far-males had higher individual quality. All this together supports the idea that the road exerts a selective effect, producing disruptive selection on the lizards’ phenotype and, therefore, may have an evolutionary impact on this population.
Murcia
