Dynamics and origins of socially induced plasticity of behaviour

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Desert locusts are notorious insect pests that periodically devastate crops and pastures at considerable human and economic cost. Unlike other grasshoppers, locusts can reversibly change between two dramatically different forms, one of which is configured for a life in migratory swarms. This transformation, or Phase Change, is driven by large fluctuations in population density. At low population densities locusts occur in the Solitarious Phase, where they are cryptic in appearance and behaviour, and most importantly, actively avoid other locusts. When locusts are forced together, they transform into the Gregarious Phase. Gregarious locusts look very different and are highly active, but crucially are attracted towards other locusts so that they can eventually aggregate into swarms. The change from solitarious to gregarious behaviour takes just a few hours whereas physical changes take several generations. We have previously demonstrated that a surge in the brain chemical serotonin during the early stages of crowding triggers this rapid change in behaviour, although how it does so is unknown. Serotonin has similarly important roles in many other animals, including humans, where it is involved in the regulation of mood and aggression. We now seek to understand how serotonin sets phase change in train, and whether phase change has arisen from behavioural traits such boldness/shyness or activity/quiescence that define 'personality' differences in other animals. We wish to determine whether such basic traits have been co-opted during evolution into the process of phase change, thus explaining their common regulation through serotonin. We will examine this by contrasting locust strains that show differing propensity to change phase, and by contrasting closely related species that do not swarm at all.Our research makes use of sophisticated automatic movement tracking systems to test the behaviours of locusts faced with different 'problems' such as moving to food across an open space or responding to a crowd of other locusts. We couple these analyses with biochemical techniques for measuring serotonin and other neurochemicals in the same animals, so we can begin to determine what governs the different and changing expressions of behaviour. We will use drugs (including some that are used in humans) to manipulate the serotonin pathway, and electrophysiological methods to record from particular serotonin-containing nerve cells that we suspect are critical to phase change. Our research will use a technique called fast scan cyclic voltammetry to measure the release of serotonin in ways that have not previously been possible in insects, and we will work with a new statistical software company to develop and use innovative analyses of behaviour. A core part of our work is to build on a number of international collaborations including one recently agreed with the Centre for Locust Control in Mauritania. Through these partnership we will gain access to wild locusts that provide an important contrast to the lab strains we already have. Research visits between the labs and field station will permit new insights for both teams of workers. The University of Leicester has recently invested more than £100k in a world-leading locust research facility to support our work.The key outcomes of our work will be: (1) an increased understanding of the processes leading to the formation and dissipation of locust swarms, with potential applications to swarm control; (2) new insights into the evolution of phase change and its relationship to fundamental behavioural characteristics; (3) increased understanding of the biochemical pathways through which serotonin works, and of how these pathways can be co-opted into new behaviours; and (4) new international and commercial collaborations.