title: Warning signals are under positive frequency-dependent selection in nature.
abstract: Positive frequency-dependent selection (FDS) is a selection regime where the fitness of a phenotype increases with its frequency, and it is thought to underlie important adaptive strategies resting on signaling and communication. However, whether and how positive FDS truly operates in nature remains unknown, which hampers our understanding of signal diversity. Here, we test for positive FDS operating on the warning color patterns of chemically defended butterflies forming multiple coexisting mimicry assemblages in the Amazon. Using malleable prey models placed in localities showing differences in the relative frequencies of warningly colored prey, we demonstrate that the efficiency of a warning signal increases steadily with its local frequency in the natural community, up to a threshold where protection stabilizes. The shape of this relationship is consistent with the direct effect of the local abundance of each warning signal on the corresponding avoidance knowledge of the local predator community. This relationship, which differs from purifying selection acting on each mimetic pattern, indicates that predator knowledge, integrated over the entire community, is saturated only for the most common warning signals. In contrast, among the well-established warning signals present in local prey assemblages, most are incompletely known to local predators and enjoy incomplete protection. This incomplete predator knowledge should generate strong benefits to life history traits that enhance warning efficiency by increasing the effective frequency of prey visible to predators. Strategies such as gregariousness or niche convergence between comimics may therefore readily evolve through their effects on predator knowledge and warning efficiency.
authors: Centre d'Ecologie Fonctionnelle et Evolutive, UMR 5175 CNRS - Université de Montpellier - EPHE - Université Paul Valéry, 34293 Montpellier 5, France; Institut de Systématique, Evolution, Biodiversité, UMR 7205 CNRS MNHN UPMC EPHE, Muséum National d'Histoire Naturelle, 75005 Paris, France mathieu.chouteau@cefe.cnrs.fr.
authors: Mathieu
authors: M
authors: Chouteau
authors: Institut de Systématique, Evolution, Biodiversité, UMR 7205 CNRS MNHN UPMC EPHE, Muséum National d'Histoire Naturelle, 75005 Paris, France.
authors: Mónica
authors: M
authors: Arias
authors: Centre d'Ecologie Fonctionnelle et Evolutive, UMR 5175 CNRS - Université de Montpellier - EPHE - Université Paul Valéry, 34293 Montpellier 5, France;
authors: Mathieu
authors: M
authors: Joron
mesh_terms: D000818:Animals; D005075:Biological Evolution; D000067558:Biological Mimicry / Q000235:genetics* / Q000502:physiology*; D002080:Butterflies / Q000235:genetics* / Q000502:physiology*; D020387:Food Chain; D056084:Genetic Fitness; D008954:Models, Biological; D010641:Phenotype; D010858:Pigmentation / Q000235:genetics / Q000502:physiology; D012641:Selection, Genetic
keywords: Müllerian mimicry; aposematism; butterflies; predation; warning signal