Mormon cricket ecology and evolution
I've been working on a number of projects investigating the behavioral and ecological mechanisms underlying migratory band formation and movement in the Mormon cricket, Anabrus simplex (Tettigoniidae). Mormon crickets can form huge migratory bands in the western U.S. consisting of millions of individuals that travel en masse up to 2 km/day and can devastate agricultural areas (see photo above). Despite the obvious similarities between migratory bands of Mormon crickets and those of locusts, my laboratory work on Mormon cricket behavior demonstrated that the behavioral mechanisms underlying band formation and movement are quite different in the two groups (Sword, 2005).
In collaboration with Pat Lorch (Kent State university) and Darryl Gwynne (University of Toronto, Mississauga), we have been using radiotelemetry, GPS, and GIS to examine the landscape-scale movement patterns of individual Mormon crickets within migratory bands. To date, we have tested hypotheses about differences between the movement patterns of individuals in outbreak and non-outbreak populations (Lorch et al. 2005), and also examined the effects of various environmental and social cues on migratory band movement patterns.
We recently performed a manipulative experiment demonstrating for the first time that Mormon crickets and locusts form migratory bands as part of an anti-predator strategy (Sword et al., 2005). However, once these groups form, individuals in the group must contend with increased competition for resources as well as the threat cannibalism. In a really neat set of experiments conducted this past summer with Steve Simpson (University of Sydney) and Iain Couzin (Princeton/Oxford), we demonstrated that Mormon crickets in migratory bands move for two reasons: 1) to exploit new nutritional resources, namely protein and salt, and 2) to avoid being eaten by hungry conspecifics approaching from the rear (Simpson et al. 2006). These findings provided a unique demonstration of the nutritional basis of mass movement and a novel perspective on the mechanisms underlying collective animal movement patterns. In short, Mormon cricket migratory band movement is a forced march driven by cannibalism. Run!!!
As an analog to the phylogenetic analysis of swarming in Schistocerca locusts, I am completing a mtDNA-based phylogeographic analysis of Mormon crickets throughout their range in western North America. This will provide a phylogenetic framework upon which to examine population-level variation in migratory behavior and its relationship to environmental factors such as the insects' nutritional environment. This study also facilitated the discovery of a cryptic species of Anabrus in Washington state, USA identified through variation in cytochrome oxidase (COIII) mtDNA sequence data (Sword et al. in preparation).
Simpson, S.J.*, Sword, G.A.*, Lorch, P.D. & Couzin, I.D. (2006) Cannibal crickets on a forced march for protein and salt. Proceedings of the National Academy of Science USA 103:4152-4156. (* equal contributors)
Sword, G.A. (2005) Local population density and the activation of movement in migratory band-forming Mormon crickets. Animal Behaviour 69(2):437-444.
Sword, G.A., Lorch, P.D. & Gwynne, D.T. (2005) Migratory bands give crickets protection. Nature 433:703.
Lorch, P.D., Sword, G.A., Gwynne, D.T. & Anderson, G.L. (2005) Radiotelemetry reveals differences in individual movement patterns between outbreak and non-outbreak Mormon cricket populations. Ecological Entomology 30:548-555.