title: Density-dependent aposematism in the desert locust.
abstract: The ecological processes underlying locust swarm formation are poorly understood. Locust species exhibit phenotypic plasticity in numerous morphological, physiological and behavioural traits as their population density increases. These density-dependent changes are commonly assumed to be adaptations for migration under heterogeneous environmental conditions. Here we demonstrate that density-dependent nymphal colour change in the desert locust Schistocerca gregaria (Orthoptera: Acrididae) results in warning coloration (aposematism) when the population density increases and locusts consume native, toxic host plants. Fringe-toed lizards (Acanthodactylus dumerili (Lacertidae)) developed aversions to high-density-reared (gregarious-phase) locusts fed Hyoscyamus muticus (Solanaceae). Lizards associated both olfactory and visual cues with locust unpalatability, but only gregarious-phase coloration was an effective visual warning signal. The lizards did not associate low rearing density coloration (solitarious phase) with locust toxicity. Predator learning of density-dependent warning coloration results in a marked decrease in predation on locusts and may directly contribute to outbreaks of this notorious pest.
authors.affiliation: Department of Zoology, University of Oxford, UK. gsword@uts.cc.utexas.edu
authors.forename: G A
authors.initials: GA
authors.lastname: Sword
authors.forename: S J
authors.initials: SJ
authors.lastname: Simpson
authors.forename: O T
authors.initials: OT
authors.lastname: El Hadi
authors.forename: H
authors.initials: H
authors.lastname: Wilps
mesh_terms: D000818:Animals; D001522:Behavior, Animal; D005247:Feeding Behavior; D006110:Grasshoppers / Q000502:physiology*; D008116:Lizards / Q000502:physiology*; D011156:Population Density; D011157:Population Dynamics