The effect of the neuropeptide [His7]-Corazonin on phase-related characteristics in the Central-American locust Schistocerca piceifrons.
Locusts exhibit one of the most extreme forms of phenotypic plasticity, named density-dependent phase polyphenism. They exist in two distinct phenotypes, called solitarious phase and gregarious phase, that are found under low and high population densities respectively. The two phases differ in nymphal coloration, morphology, behavior, physiology, reproduction, among other traits. Solitarious nymphs are usually green, relatively inactive, and avoid each other, while gregarious nymphs exhibit a very obvious yellow/orange background with black patterning, are highly active and are attracted to each other. The multifunctional neuropeptide [His7]-Corazonin is currently one of the best-known molecular agents to influence density-dependent phase polyphenism. It has been shown to strongly affect black coloration in at least two species of locusts, the desert locust Schistocerca gregaria and the migratory locust Locusta migratoria. In addition, it was shown to have a gregarizing effect on morphometric values and on the amount of antennal sensilla, two other phase-related characteristics. No effect of Corazonin was found on other phase-related characteristics, including behavior. Density-dependent phase polyphenism has evolved independently multiple times, meaning the effect of Corazonin might not be conserved in all locusts. Nonetheless, the effect of Corazonin has only been investigated in two out of about twenty locust species. I aimed to investigate the effect of Corazonin in Schistocerca piceifrons, which is closely related to S. gregaria but still represents an independent origin of density-dependent phase polyphenism. I generated a dsRNA construct that strongly reduced Corazonin expression upon injection, and used this construct to test the influence of Corazonin on nymphal coloration, morphometrics, and behavior in crowded-reared last instar nymphs. The knockdown of Corazonin very strongly reduced black coloration, and also altered the morphometrical values of females towards the expected values of solitarious individuals. Last, I did not find any effect of Corazonin on the behavior or on the solitarizaiton of crowded-reared nymphs. Together, our data suggests Corazonin is a major player in the regulation of density-dependent phase polyphenism in S. piceifrons, and that this role of Corazonin is conserved between different locust species.