Defence tactics cycle with diel microhabitat choice and body temperature in the desert locust,Schistocerca gregaria

Abstract

AbstractWe examined environmental factors influencing plasticity in antipredator defences of adult gregarious desert locusts,Schistocerca gregaria, including daily cycles in temperature, light, microhabitat occupied and predator threat. In the Sahara Desert in Mauritania, West Africa, daily temperature fluctuated widely from below locusts’ cold thermal limits for jump‐ and flight‐defence, to above their preferred body temperature. Locusts changed microhabitats throughout the 24‐hr period in synchrony with the daily thermo‐photocycle. They roosted in tall trees and large bushes at night, moved to the ground in the morning, shaded under or in small bushes and annuals at midday, moved back to the ground in the afternoon and then returned to night roosting sites around dusk. Locust antipredator defences varied throughout the 24‐hr period, and these changes were correlated with temperature, photocycle and habitat. Flight escape was associated with daytime, high temperatures and the ground habitat. Dropping escape (= releasing hold of vegetation and dropping to the ground or into vegetation) was associated with cool temperatures and low‐to‐medium sized bushes. Stationary behaviour was associated with the tree microhabitat and height off the ground. Roosting (a primary defence) was associated with cool temperatures at night and early morning, tree habitats and nocturnal ground‐foraging times of endothermic mammals. In summary, we propose that temperature is the key factor in determining both changing microhabitat choice and changing antipredator defence, due to thermal constraints on locust muscle for this ectothermic insect. The thermocycle also influences temporal predator loads, which influence the evolution of locust diel defence strategies. These various environmental factors not only influence one another, they also interact to influence antipredator defence expression in locusts. Overall, our study suggests that plasticity in locust antipredator defences is a complicated matter mediated by the interactions of multiple environmental factors and physiological and ecological constraints and trade‐offs.