A solitarious male Desert locust (left) facing a gregarious male (right) of the same species.

Mechanisms of Behavioural Plasticity in Locust Swarm Formation

My research is aimed at understanding the mechanisms that permit animals to adapt their brains, bodies and behaviour to changing environmental conditions. As a model we use the Desert Locust, Schistocerca gregaria, a grasshopper (family Acrididae) that is capable of an extreme and economically damaging form of such environmentally driven plasticity.

Desert locust swarms are a serious threat to agriculture across Africa and Asia. These devastating outbreaks are the ultimate manifestation of the capacity of locusts to transform between two radically different phenotypes: a shy and inconspicuous Solitarious Phase and a brightly-coloured, group-living Gregarious Phase. The transformation between the two phases is caused entirely by changes in local population density.

In a recent breakthrough discovery, we found that the initial transition to gregarious behaviour is mediated by a surge of the neurochemical serotonin in the locust's nervous system. Serotonin is present in the brains of all animals, and in humans plays an important role in controlling our interactions with each other and the world.

We now seek to understand how serotonin affects neurons within individuals, which in turn leads to changes in how locusts interact with each other, driving a reinterpretation of the locust genotype to yield a profoundly different phenotype.

This research problem intrinsically spans many levels of biological process and therefore demands a broad and interdisciplinary approach that links genes and signalling molecules, nerve cells and their connections, behaviour and anatomy, group interactions and ecology. Accordingly we make use of a wide range of techniques including the quantitative analysis of behaviour, electrophysiology of identified neurones and circuits, laser confocal microscopy and image analysis, transcriptomics and proteomics, and biochemical and molecular analyses of neural signalling mechanisms.

Understanding the mechanisms by which locusts change phase will ultimately help develop more targeted control methods that prevent the formation of swarms and at the same time lessen the collateral damage caused by pesticides. The wider significance of our research is in gaining a deeper understanding of the mechanisms that integrate genetic and environmental information to coordinate the expression of complex phenotypes. Humans and insects share fundamental mechanisms through which changes in our environment affect the workings of our brains, the nature of our interaction with conspecifics, and ultimately who we are.

Nitric Oxide Signalling in Invertebrate Nervous Systems

I also have a long-standing research interest in nitric oxide (NO), an unusual signalling molecule with an evolutionarily conserved role in learning and memory. Unlike conventional neurotransmitters, NO is highly diffusible and may thus spread freely from its release sites. To what extent such "volume signalling" does indeed occur in the brain and to what end it is used has remained contentious, however. I have resolved long-standing uncertainties about the expression architecture of NO synthase in invertebrate nervous systems and the results implicate NO in an unexpectedly diverse array of functions. I have combined anatomical analysis of NO source and NO target neurones with computer models of NO diffusion to show that NO signals can indeed spread over tens of micrometers and thus by-pass the point-to-point connectivity of synaptic networks. An exciting future extension of this work will be to exploit the experimental advantages offered by invertebrate nervous systems for characterising the spatio-temporal dynamics of NO in vivo and its effects on the processing of sensory information in the nervous system.

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