The Neurobiology of a Transformation from Asocial to Social Life During Swarm Formation in Desert Locusts

摘要

Many species display complex social interactions and for such animals other members of their species can form a major or even dominant part of their environment. Social interactions between these animals can induce long-lasting changes in brain function and behaviour that in turn alter the ways in which they respond to each other. Locusts are insects that can change reversibly between an asocial solitarious phase and a social gregarious phase that is driven by changes in population density. Phase change encompasses both a socially driven mechanism and multifaceted changes in behaviour, physiology, neurochemistry, brain morphology and even appearance. At low densities, locusts occur in the solitarious phase. Their biology is governed by the need to be inconspicuous and they actively avoid other locusts, thus maintaining their low population density. When sheer population size and scarce resources force solitarious locusts together despite their aversion to each other, a transformation is triggered that results in the gregarious phase. The stimuli responsible for starting this transformation are provided by other locusts, notably mechanosensory stimulation resulting from inadvertent jostling of each other. After just a few hours these stimuli induce changes in behaviour, including, critically, a change toward a propensity to be attracted towards other locusts. This attraction initiates a positive feedback loop whereby the continual presence of other locusts provides the necessary stimuli to drive the process towards the extreme gregarious phenotype and eventually to swarming. The biology of gregarious locusts is then dominated by the demands of group living. There is