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Density-dependent aposematism in the desert locust.
G A Sword1, S J Simpson, O T El Hadi
1Department of Zoology, University of Oxford, UK. gsword@uts.cc.utexas.edu
Proceedings. Biological Sciences
|February 12, 2000
Summary
Desert locusts develop warning coloration when consuming toxic plants, signaling toxicity to predators. This density-dependent aposematism reduces predation and may drive locust outbreaks.
Area of Science:
- Ecology
- Evolutionary Biology
- Animal Behavior
Background:
- Locust swarm formation mechanisms remain unclear.
- Locusts display density-dependent phenotypic plasticity, often attributed to migration.
- The role of coloration in locust ecology is under-investigated.
Purpose of the Study:
- To investigate the function of density-dependent color change in desert locusts (Schistocerca gregaria).
- To determine if gregarious-phase coloration serves as aposematic signaling.
- To assess predator learning and aversion to toxic locusts.
Main Methods:
- Rearing desert locust nymphs at high densities and feeding them toxic host plants (Hyoscyamus muticus).
- Observing color changes in gregarious-phase locusts compared to solitarious-phase locusts.
- Presenting locusts (different phases and diets) to fringe-toed lizards (Acanthodactylus dumerili) to assess predator learning and aversion.
Main Results:
- Gregarious-phase desert locusts exhibited warning coloration.
- Fringe-toed lizards learned to associate gregarious-phase locusts with toxicity, developing an aversion.
- Lizards primarily used visual cues (coloration) and olfactory cues to associate locusts with unpalatability.
- Solitarious-phase locust coloration did not elicit a learned aversion.
Conclusions:
- Density-dependent color change in desert locusts functions as aposematism, signaling toxicity acquired from host plants.
- Predator learning of this warning coloration reduces locust predation.
- Aposematic signaling in locusts may contribute to population outbreaks.