Ecological correlates of colour pattern polymorphism along the transition zone between two morphs of the common wall lizard, Podarcis muralis

The ecological correlates of dorsal colour pattern polymorphism were studied along the transition zone between two supposed subspecies ( = colour pattern types in this article) of the common wall lizard, Podarcis muralis, in a hilly area of Latium, Central Italy. In this area two supposed subspecies, i.e. P. m. brueggemanni and P. m. nigriventris, are known to occur. Lizards were studied along 500 m long transects within three different habitat types, i.e. wood, wall, and bushy pasture. A total of 279 adult lizards (154 males, 125 females) were examined. Three colour morphs were observed at each site, i.e. brueggemanni type (brown-green upper parts), nigriventris type (black-green upper parts), and a colour morph intermediate between the two. The distribution and abundance of brueggemanni and nigriventris colour morphs was clearly non-random across habitat types: brueggemanni was abundant in walls and bushy pastures, and nigriventris in wood. To explain the observed pattern we tested the hypothesis of a differential predation exposure by the various colour morphs in different habitats by analysing the differences between colour morph frequencies of lizards with intact tail and with broken/regenerated tail in the various habitats of the study area. Our analysis would not support the differential predation-risk hypothesis, because the frequency of individuals with broken tails was very similar in the three colour morphs among different habitats.