Color-assortative mating in a color-polymorphic lacertid lizard

Color polymorphisms are common in lizards, which provide an excellent model system to study their evolution and adaptive function. The lacertid genus Podarcis is particularly interesting because it comprises several polymorphic species. Previous studies with lacertid lizards have tried to explain the maintenance of color polymorphisms by correlational selection between color morphs and several phenotypic traits. Particular attention has been paid to their putative role as signals reflecting alternative reproductive strategies under frequency-dependent selection, but the relationship between mating patterns and color polymorphism has not been previously considered. In this study, we use longitudinal behavioral data obtained during six consecutive breeding seasons (2006–2011) in a free-ranging polymorphic population of Podarcis muralis lizards to examine the hypothesis that lizards mate assortatively by color. We provide spectrophotometric data that confirm the existence of discrete color morphs and show that morphs are ontogenetically stable once they develop fully in sexually mature individuals. We also present data on the year-to-year variation of relative morph frequencies. Finally, we provide evidence that, over a 6-year period, homomorphic male–female pairs in the wild were significantly more common than heteromorphic pairs. Taken together, our results suggest that color assortative mating may be involved in the maintenance of discrete color morphs in this and other lacertid species.