Repeated pause-or-go decisions of individuals are instrumental in the coordinated marching of locust swarms (#227)
The coordinated activity of locust swarms has always been a challenge to laymen and scientists alike. As part of our ongoing effort to decipher the rules governing locust coordinated behaviour, we used video-recording and cutting-edge movement tracking methods to monitor the marching behaviour of five-instar desert locust nymphs. A group of crowd-reared nymphs in our experimental system spontaneously generated robust and consistent coordinated marching. Using high temporal and spatial resolution analysis, we investigated the early stages and maintenance of this behaviour, from global properties of the swarm, to the movement patterns of individuals and the effective social interaction between conspecifics. A major feature of the behaviour of individuals within the crowd was intermittent switching between standing and walking, triggered by tactile and/or visual stimuli. This intermittent motion pattern constitute a sequence of individual decisions in which animals repeatedly reassess their situation and their environment, and decide whether or not to swarm. Accordingly, we introduced a new agent-based modelling approach in which pause-and-go motion is pivotal. This interpretation explains several macroscopic observables of the entire swarm, for example, the measured correlation between the order parameter (which quantifies the level of synchronization) and the fraction of walking animals. Theoretically, it implies the existence of generic characteristics in the emergence of collective order in swarms. The suggested instrumental role of visual stimuli was further augmented by neurophysiological experiments showing that the Descending Contralateral Movement Detectors (DCMD, a pair of interneurons instrumental in directing visual sensory inputs to motor centres) are sensitive to stimuli related to approaching and receding walking insects. Furthermore, the DCMD of gregarious animals showed a more adapted response to the visual trigger observed (compared to solitary-reared animals). We are currently further investigating the effects of a changing environment on the behaviour of the individual locusts and the swarm. We are also looking at the marching locusts as inspiration for swarming robots.
- Ariel G., Ophir Y., Levi S., Ben-Jacob E. and Ayali A. (2014) Individuals’ intermittent motion is instrumental to the formation and maintenance of swarms of marching locust nymphs. PLoS One 9(7): e101636.
- Ariel G. and Ayali A. Modeling locust collective motion: A review. Submitted for publication