Male-male aggression is unlikely to stabilize a poison frog polymorphism

Phenotypic polymorphism is common in animals, and the maintenance of multiple phenotypes in a population requires forces that act against homogenizing drift and selection. Male-male competition can contribute to the stability of a polymorphism when males compete primarily with males of the same phenotype. In and around a contact zone between red and blue lineages of the poison frog Oophaga pumilio, we used simulated territorial intrusions to test the non-exclusive predictions that males would direct more aggression toward males of (i) their own phenotype and/or (ii) the phenotype that is most common in their population. Males in the monomorphic red and blue populations that flank the contact zone were more aggressive toward simulated intruders that matched the local coloration. However, males in the two polymorphic populations biased aggression toward neither their own color nor the color most common in their population. In sympatry, the rarer color morph gains no advantage via reduced ...