Visual stimuli as triggers for collective movement in desert locust nymphs
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1
Tel Aviv University, Department of Zoology, Faculty of Life Sciences, Israel
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2
Bar Ilan University, Department of Mathematics and Computer Science, Israel
Collective behavior can be found at all levels of organization, from single cells to animal communities. It constitutes an important behavioral pattern with implications for both the living and the man-made environment. Several systems currently serve as models for the study of mechanisms of collective behavior. From biblical times and still today, the devastating effects of mass migrating insects, specifically those of the desert locust (Schistocerca gregaria), have attracted much attention. However, our understanding of swarm formation and of the complex interactions within a locust swarm is still very far from complete. Synchronized movement is seen not only in flying adult locusts but also in bands of juveniles, in which the wingless hoppers form a marching swarm that can extend over kilometers. What are the mechanisms that allow a swarm to move in coordination?
We used video recording and cutting-edge methods of movement tracking to monitor the marching behavior of five-instar desert locust nymphs. Previous work has demonstrated that aligned marching depends on the animals' density, and defined the critical density value required for the formation of such movement. Further findings suggested that both tactile and visual stimuli take part in coordinating the collective movement. 30-50 crowd-reared locusts in our experimental system will spontaneously generate robust and consistent coordinated marching behavior. Using high temporal and spatial resolution analysis in a MatLab environment, we investigated the early stages and maintenance of this behavior. Individual animals within the crowd intermittently switch between standing and walking, a switch that can be triggered by tactile or visual stimuli. We show that initiation (or resumption) of walking that is preceded by touch is more likely to occur when it is accompanied by an increase in the number of close-range surrounding moving animals. In contrast, a walking event that is not triggered by a tactile stimulus, depends on a decrease in the number of moving animals in close proximity. Regardless of the presence of tactile stimuli, an increase in the average velocity of close-range surrounding moving animals is a major visual trigger for the initiation of walking by a standing individual.
These findings suggest a dominant role of visual stimuli in establishing and maintaining synchronized movement in marching locust bands. While continuing to study further collective behavioral rules in the system, we also take advantage of the locust as an established neurophysiological preparation in order to investigate the underlying neural mechanisms that allow this collective behavior among locusts.
Keywords:
gregarious behavior,
Schistocerca gregaria,
swarm
Conference:
Tenth International Congress of Neuroethology, College Park. Maryland USA, United States, 5 Aug - 10 Aug, 2012.
Presentation Type:
Poster (but consider for student poster award)
Topic:
Sensorimotor Integration
Citation:
Ophir
Y,
Ariel
G and
Ayali
A
(2012). Visual stimuli as triggers for collective movement in desert locust nymphs.
Conference Abstract:
Tenth International Congress of Neuroethology.
doi: 10.3389/conf.fnbeh.2012.27.00200
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Received:
29 Apr 2012;
Published Online:
07 Jul 2012.
*
Correspondence:
Mr. Yotam Ophir, Tel Aviv University, Department of Zoology, Faculty of Life Sciences, Tel Aviv, 69978, Israel, yotamophir@gmail.com