Current Biology, PNAS: Cannibalism and collective behavior in swarming insects

Posted by on Sep 24 2009 in HeadlinesNo comment

One of the most striking and devastating examples of collective movement is exhibited by locusts. Swarms of the desert locust, Schistocerca gregaria, can devour large areas of vegetation and have a huge social and economic impact on humans, affecting the livelihood of one in ten people on the planet in plague years. How do these destructive swarms form and what is the mechanism that drives swarming in locusts? Understanding the governing factors and resulting consequences of mass animal movements is critical not just for the control of pest species, such as locusts, but is an important component of many other ecological and evolutionary processes, for example, animal migration, the spread of diseases, habitat fragmentation, and climate change.

Collective animal movements, such as marching bands of juvenile locusts, form as a result of individuals interacting with one another. Aggressive cannibalistic interactions amongst individuals are prevalent in natural populations of locusts. Individuals in marching bands tend to bite others but risk being bitten themselves. We have been examining how cannibalism between individuals affects the collective motion of juvenile locust nymphs by studying marching bands in the laboratory. Through the manipulation of individuals’ capacity to detect different stimuli (mechanosensory and visual) we can understand how these cues influence the collective motion of locust groups and also the inherent behaviour of locusts when alone.

Reducing individuals’ ability to detect tactile stimuli can be achieved by denervating individuals’ abdomen thereby reducing sensitivity to contact from behind, and visual stimuli can be manipulated through occlusion of the eyes.

The motion of individuals in an experimental arena can measured using automated tracking software. Such manipulations resulted in a reduction in the motion of individuals in a group and an increase in cannibalism. Cannibalism and the threat of cannibalism from behind triggers movement. Individuals move to reduce their risk of cannibalism and also bite those ahead, stimulating further motion. This suggests that coordinated mass migration in locusts may be driven by highly selfish and aggressive cannibalistic behaviour.

For additional information, you can look at Sepideh Bazazi’s website: http://www.sbazazi.com.

Relevant papers:

Guttal, V., Romanczuk, P., Simpson, S.J., Sword, G.A. & Couzin, I.D. (2012) Cannibalism as a driver of the evolution of behavioral phase polyphenism in locusts. Ecology Letters 15, 1158-1166.

Bazazi, S., Bartumeus, F., Hale, J.J., Holmin, A.J. & Couzin, I.D. (2012) Intermittent motion in desert locusts: behavioral complexity in simple environmentsPLoS Computational Biology8(5), e1002498

Bazazi, S., Pfennig, K.S., Handegard, N.O. & Couzin, I.D. (2012) Collective vortex formation and foraging in polyphenic spadefoot toad tadpolesBehavioral Ecology and Sociobiology, 66(6), 879-889.

Bazazi, S., Romanczuk, P., Thomas, S., Schimansky-Geier, L., Hale, J. J., Miller, G. A., Sword, G.A., Simpson, S.J. and Couzin, I.D. (2011) Nutritional state and collective motion: from individuals to mass migrationProceedings of the Royal Society of London Series B 278(1704), 356-363. 

Bazazi, S., Ioannou, C. C., Simpson, S. J., Sword, G. A., Torney, C. & Couzin, I. D. (2010) The social context of cannibalism in Mormon cricket collective movementPLoS ONE 5(12), e15118.

Escudero, C., Yates, C. A., Buhl, J., Couzin, I. D., Erban, R., Kevrekidis, I. G., & Maini, P. K. (2010) Ergodic directional switching in mobile insect groupsPhysical Review E 82(1), 011926.

Simpson, S. J., Raubenheimer, D., Charleston, M. A., Clissold, F. J., Couzin, I. D., & Clements, K. D., et al. (2010) Modelling nutritional interactions: from individuals to communities.Trends in Ecology and Evolution 25(1), 53-60. 

Yates, C. A., Erban, R., Escudero, C., Couzin, I. D., Buhl, J., & Kevrekidis, I. G., et al. (2009). Inherent noise can facilitate coherence in collective swarm motionPNAS 106(14), 5464-5469.

Romanczuk, P., Couzin, I.D. & Schimansky-Geier, L. (2009) Collective motion due to individual escape and pursuit responsePhysical Review Letters 102(1), doc# 010602.

Bazazi, S., Buhl, J., Hale, J.J., Anstey, M.L., Sword, G.A., Simpson, S.J. & Couzin, I.D. (2008) Collective motion and cannibalism in locust migratory bandsCurrent Biology 18(10), 735-739.

Buhl, J., Sumpter, D.J.T, Couzin, I.D., Hale, J., Despland, E., Miller, E. & Simpson, S.J. (2006) From disorder to order in marching locustsScience 312, 1402-1406.

Simpson, S.J., Sword, A.G., Lorch, P.D. & Couzin, I.D. (2006) Cannibal crickets on a forced march for protein and saltPNAS 103, 4152-4156.

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