Behavioral plasticity in anti-predator defense in the desert locust

Animals sometimes switch antipredator defense tactics as they move among different microhabitats or experience different body temperatures. However, it remains unclear how ectothermic prey animals alter defensive behaviors to habitat and thermal conditions jointly. We addressed this question in adult desert locusts (Schistocerca gregaria) in the Sahara Desert of Mauritania, by recording how changing microhabitat (size of roosting-plant) and temperature influenced three alternative defenses (flying, dropping, or remaining motionless), in response to a simulated ground predator. Both habitat structure and body temperature influenced locust defense behavior, and these two factors interacted. Flight escape was the preferred defense when temperatures were above the minimum threshold for locust flight (∼22 °C). At low temperatures, defense response to predator threat varied with plant size and locust height off the ground: locusts in low bushes dropped to the center of the bush and hid, whereas those above ∼2 m in trees remained stationary. These alternative defense behaviors appear to be adaptive under the different environmental conditions. Flight escape is extremely effective, but cannot be performed under ∼22 °C. Hence, alternative defenses (dropping or remaining stationary) are necessary. These defenses are effective at low temperatures, because dynamic locomotion is not required. Our results suggest that desert locusts integrate information about microhabitat, temperature, and threat characteristics to adaptively adjust defense tactics.