The main goal of this study was to investigate the appearance of asymmetry in the bodies of the common wall lizard (Podarcis muralis) and Horvath's rock lizard (Iberolacerta horvathi), as well as how these asymmetries are connected to the following potential stress factors: altitude, urbanization and the presence of another species (interspecific competition). In addition, we also made an interspecific comparison of morphological body characteristics. We used geometric morphometric methods to create landmark coordinates in the photographs of the upper side of lizards' heads, which were useful for our comparative analysis. Modified ANOVAs and an asymmetry index were used to find the differences in four physical characteristics: shape and size of the head, body size and the number of supraciliar scales. We included sixteen populations of both species from different locations across Slovenia and Croatia. We found out that there is a presence of fluctuating asymmetry in the number of supraciliar scales and the shape of the head in all of our samples. Results have shown that both species had more asymmetric heads in the middle altitude levels. We think there might be other factors, like lower availability of suitable habitats or higher presence of syntopic populations, indirectly affecting this result. In populations of the common wall lizard living in urban environment, we have not found any more asymmetries compared to those living in natural environments. We have also not found more asymmetries in syntopic populations, we actually found more asymmetries of supraciliar scales in allotopic populations. Biotic interactions probably do not have such a big effect that would cause asymmetries in the studied lizards in syntopy. Horvath's rock lizards had more asymmetric heads, which indicates they might be exposed to greater environmental stress or the reason could also be genetical, since the analyses have shown presence of directional asymmetry.
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