Differenze di nicchia termica tra i morfi cromatici di Podarcis muralis

The co-occurrence of different morphs within the same population represents an intriguing challenge for evolutionary biologists, since their maintenance should be associated to the coexistence of alternative adaptative strategies. In this scenario, the common wall lizard (Podarcis muralis) exhibits a typical chromatic polymorphism in ventral colouration (red, R; white, W; yellow, Y) which has been already associated to physiological and ethological differentiation. Here we investigate if the three morphs show also ecological differences with respect to the thermal microhabitat conditions, which may play a crucial role in a small ectothermic species. The studied population inhabited a wall surrounding a city-park in Cesano Maderno (45.62°N, 9.15°E). On June, 2013 we recorded the positions of 53 adult lizards in a 50 cm ˟ 50 cm grid virtually superimposed to the wall. By using a thermal camera, we took a picture to characterize the thermal properties of each cell (mean and standard deviation of the temperature; proportion of pixel with temperature higher than the mean plus one standard deviation). We built the maximum entropy models of the thermal niche of each morph and then compared them using the fuzzy-k statistic. Mean temperature was excluded since it was spatially correlated with the vertical position of the cells. Each model was tested against the null hypothesis of no relationship with thermal variables, and performed better than chance. All the comparisons gave low k values, suggesting the three morphs having different thermal niches. R and Y showed a stronger relationship with the thermal variables than W and also a different kind of response to them, being R more affected by temperature standard deviation, Y also by the percentage of hot pixels, and W an intermediate case. These results supported, for the first time, the hypothesis of the occurrence of ecological differences between the three morphs of P. muralis.