Better to be resident, larger or coloured? Experimental analysis on intraspecific aggression in the ruin lizard

Territoriality evolves when the benefits gained from exclusive access to limited resources exceed the costs of defence. Sometimes animals evolve distinct morphs, that may reflect different capability, and in some territorial species of lizards the polymorphism is associated to alternative strategies, both for reproductive efficiency and territorial dominance. It is known that normally larger males are more aggressive and are able to defend a larger area and for longer than small males; in fact this dynamic is widespread in many animal species including the genus Podarcis. The aim of our study was to test which factors determine the outcome of fighting in the strongly territorial Italian ruin lizard, Podarcis siculus, using two types of contests: (1) resident versus intruder and (2) in a neutral arena. Furthermore, because these lizards are characterized by strong ventral colour variability, usually restricted to jaws and throat, we wanted to investigate if coloured lizards have higher chances at winning than white lizards. The results showed that the fight's result was significantly influenced by the state of residence, while the colour had no effect; instead, the snout to vent length difference between opponents had significant influence on the outcome in the neutral arena. Our results suggest that, in this lizard, both the size and the state of residency, no matter of colour, play an important role to determine the outcome of a fight, however, highly depending on the contest. We think that P. siculus should be object of future studies, focusing on behavioural and ecological aspects, even considering the occurrence of different colours within and among populations.