University of Lincoln Liverpool, England, United Kingdom
The same signal can convey different information across an animal’s lifetime. Desert locusts (Schistocerca gregaria) exhibit an extreme form of phenotypic plasticity called phase polyphenism, in which a suite of behavioral and morphological traits differ according to local population density. Male and female juveniles developing at low population densities exhibit green or sand-colored background-matching camouflage, while at high densities they develop contrasting yellow and black aposematic patterning that can deter predators as an interspecific signal. Adult desert locusts also express density-dependent plasticity in color, with high density inducing the expression of bright yellow coloration upon sexual maturation, particularly in males. We used RNAi gene-silencing of the carotenoid-binding ‘Yellow Protein’ gene (YP) to prevent the expression of yellowing in males at high population density. We showed that male yellowing in gregarious phase desert locusts acts as an intraspecific sexual warning signal, which forms a multimodal signal with the anti-aphrodisiac pheromone PAN to prevent mistaken sexual harassment from other males during scramble mating in a swarm. Socially-mediated re-expression of YP thus repurposes a juvenile interspecific signal that deters predators into an adult intraspecific signal that deters undesirable mates.
