Close encounters of the three morphs: does color affect aggression in a polymorphic lizard?

Color polymorphism is genetically controlled and the process generating and maintaining morphs can affect speciation and/or extinction rates. Competition and aggression among morphs can contribute to polymorphism maintenance and color badges are useful signals in intraspecific communication, because they convey information about alternative strategies and avoid unnecessary conflicts. This could lead to an uneven spatial distribution of morphs in a population, because the local frequency of each morph establishes the intensity of the competition in that neighborhood, and then the fitness of each male. We used a polymorphic lizard, Podarcis muralis, to assess if aggression varies among morphs under two contrasting hypotheses: a heteromorphic vs. a homomorphic aggression. We used laboratory mirror tests after lizard color manipulation and we verified the results consistency with the analysis of the spatial distribution of morphs in a wild population. Both the experiments confirmed that aggression is morph-specific and notably homomorphic. The adoption of behavioral alternative strategies that minimize risks and costs of unwanted conflicts could facilitate the stable coexistence of the phenotypes and reduce the resource competition. A bias in aggression to like-coloured males would advantage rarer morph, which would suffer less harassment by common morphs and obtain a fitness advantage. This process would be negatively-frequency-dependent and would stabilize polymorphism in the populations, possibly leading to sympatric speciation.