Coordinated speed oscillations in schooling killifish enrich social communication
Daniel T. Swain, Iain D. Couzin, and Naomi Ehrich Leonard
(2015), Journal of Nonlinear Science, 25:1077-1109, DOI 10/1007/s00332-015-9263-8.
Springer JNLS link
We examine the spatial dynamics of individuals in small schools of banded killifish
(Fundulus diaphanus) that exhibit rhythmic, oscillating speed, typically with sustained,
coordinated, out-of-phase speed oscillations as they move around a shallow water tank.
We show that the relative motion among the fish yields a periodically time-varying network of
social interactions that enriches visually driven social communication. The oscillations lead
to the regular making and breaking of occlusions, which we term `switching'. We show that the
rate of convergence to consensus (biologically, the capacity for individuals in groups to achieve
effective coordinated motion) governed by the switching outperforms static alternatives, and
performs as well as the less practical case of every fish sensing every other fish. We show
further that the oscillations in speed yield oscillations in relative bearing between fish over
a range that includes the angles previously predicted to be optimal for a fish to detect changes in
heading and speed of its neighbors. To investigate systematically, we derive and analyze a dynamic
model of interacting agents that move with oscillatory speed. We show that coordinated circular
motion of the school leads to systematic cycling of spatial ordering of agents and possibilities
for enriched spatial density of measurements of the external environment. Our results highlight
the potential benefits of dynamic communication topologies in collective animal behavior, and
suggest new, useful control laws for the distributed coordination of mobile robotic networks.
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