Variazione stagionale del testosterone plasmatico nei morfi di colore della lucertola muraiola (Podarcis muralis)

Identifying the processes on the basis of the evolution and maintenance of colour polymorphisms is one of the major goals in evolutionary biology. The occurrence in the same population of different morphs implies the occurrence of alternative strategies, which represent alternative, locally adapted, optima within a single species. Podarcis muralis is a small-sized lacertid that shows a marked territorial behaviour as males fight to defend their territories from other males. The species expresses a highly polymorphic coloration in ventral and throat scales, with three main morphs (i.e. white, yellow and red). In last decades, the colour polymorphism of this species has been the subject of several studies, which found so­me phenotypic differences associated with each morph. For example, divergence among morphs emerged in body size, immunecompetence in captivity, homing behaviour and reaction to stress. Levels of circulating sex hormones can play an important role, either through organizational or activational effects, in triggering the expression of these alternative reproductive morphs. We carried out a capture-recapture study in order to compare the testosterone levels of male morphs during the breeding season. Overall, we captured 463 males, but only the 76 individuals that were captured at least in two sessions were included into the analyses. Colour morphs did not differ in absolute testosterone T plasma levels, but showed a different seasonal pattern. In particular, yellow males (n = 29) had higher testosterone concentration at the beginning of the season (April) with respect to the white and red morphs (n = 35 and n=12, respectively). This pattern was completely reversed in July, when both red and yellow males had higher hormone concentration. These results have relevant implications on the mechanisms maintaining colour polymorphism in Common wall lizards.