Ventral colour polymorphism correlates with alternative behavioural patterns in female common lizards (Lacerta vivipara)

In the common lizard, female competition for resources is likely to be a strong selective pressure that has enhanced the evolution of conspicuous traits. Female common lizards display a polymorphism in ventral colour correlated with differences in reproduction, dispersal, and susceptibility to resource competition. We tested the hypothesis that this polymorphism is correlated with differences in behaviour in a social context. We studied the agonistic behaviour (aggression and avoidance) and social stress of females of different colours during laboratory-staged encounters with a limiting resource. We found that the behaviour of females was affected by their own colour, or the colour of their opponent, or both. Such alternative behavioural patterns might reflect differences in competitive ability. Orange females were the least aggressive and the most likely to avoid social interactions, and thus could be a weaker competitor. Yellow females were rarely exposed to aggression and often made their opponents flee, and thus might have higher resource-holding potential. Mixed females were aggressive but were also often exposed to aggression, and displayed the highest stress level, which could be characteristic of an intermediate or condition-dependent resource-holding potential. The possibility that ventral colour is used in social interactions to signal resource-holding potential is discussed.