Adaptive spread of a sexually selected syndrome eliminates an ancient color polymorphism in wall lizards.

Genetically determined color morphs are found in many animals. Polymorphism can be maintained by social selection if competitive interactions allow each morph to increase in frequency when rare. This reliance on negative frequency–dependent selection should make color polymorphism vulnerable to the appearance of novel phenotypes that disrupt competitive interactions among morphs. We show that the origin and adaptive spread of a sexually selected syndrome in common wall lizards (Podarcis muralis) selectively eliminates alleles coding for alternative color morphs that have been maintained for millions of years. The results demonstrate how the arrival of a novel phenotype can disrupt balancing selection, providing a link between rapid phenotypic evolution and the loss of color polymorphisms. Editor's summary: Many animal species exhibit different physical characteristics between individuals, especially when it comes to males. Lizards are particularly interesting examples, because many species have multiple versions of males. Studying these species can inform understanding of how such polymorphism evolves and operates. Uller et al. found that a recently emerged white throated morph of European wall lizards was highly preferred over an earlier three-color system, which has led to disruption of a million-year balance across the morphs (see the Perspective by Gopalan and Castoe). In related work on side-blotched lizards in the United States, Corl et al. found that a well-known morphological triad of males was generated by a two-allele system, with phenotypic plasticity at one of the alleles and a rock-paper-scissors dynamic. —Sacha Vignieri [ABSTRACT FROM AUTHOR]