Circadian rhythms in the locust nervous system
Desert locusts (Schistocerca gregaria) exist in one of two phases, solitarious or gregarious. Normally, they are in the solitarious phase in which they are camouflaged, slow-moving and active in low light. Under certain conditions, they change to the gregarious phase when they become more conspicuously coloured, move faster and become active during the daytime. They also form swarms and at this stage they are one of the most important insect pests.
Our research interests concern the ways in which some aspects of locust behaviour and physiology are controlled by an endogenous circadian rhythm and how these differ between solitarious and gregarious individuals.
This project uses extracellular electrophysiology to investigate the plasticity of the locust visual system. The responses of a visual interneuron, the descending contralateral movement detector, in locusts have been shown to vary according to whether they are in the solitarious or gregarious phase. In addition, we have now shown that there is a circadian rhythmicity in the responses of this neuron.
The figure shows the response of DCMD to an approaching object. Lower trace: a recording from the cervical connective containing the axon of DCMD revealed the neuron’s characteristic response (largest spikes). Upper trace: smoothed firing rate of DCMD. The single vertical line represents the predicted collision time.
This figure shows how DCMD’s response varied over 36 h under constant light in a gregarious locust, as shown by the number of DCMD spikes elicited by a looming stimulus presented at 1 h intervals. Shaded areas represent time periods when the locusts would have normally experienced darkness.
This is evidence of a circadian rhythm in responses of DCMD (see poster). We have shown that these responses differ in solitarious and gregarious locusts and that the time of peak responsiveness coincides with the time at which peak flying activity is seen in these animals.
Current research includes an investigation into circadian rhythmicity in the activity of locust of the two different phases.
Gaten E., Huston S., Dowse H. & Matheson T. (2012) Solitary and Gregarious Locusts Differ in Circadian Rhythmicity of a Visual Output Neuron. Journal of Biological Rhythms: 27, 196-205.
This work is being carried out with Dr Tom Matheson and Dr Tom Nielson, Department of Biology in association with Dr S. Ott, Prof M Burrows and Dr S Rogers, Department of Zoology, University of Cambridge.