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Computational exploration of treadmilling and protrusion growth observed in fire ant rafts

Fig 3

Comparing Treadmilling Dynamics.

(A-B) The gradient of contractile speed, , towards the anchor point of the rafts (red dot) is illustrated via heat maps within defined regions of interest (ROIs) for both (A) an experimental and (B) simulated raft. was computed as the component of speed moving towards the stationary reference frame (i.e., the acrylic rod) and was measured for every point within these 2D ROIs, then averaged over durations exceeding 13 minutes. Scale bars represent 10 ℓ. (C) is plotted with respect to distance from the anchor point, r, for both the experiment (discrete red squares) and simulation (solid black curve). The slopes of the least-squares regression lines are taken as the average contractile strain rate . The experimental strain rate () agrees with the numerical value (). (D-E) The growth zones of both (D) an experimental and (E) simulated raft after roughly 50 min are shaded in cyan. Scale bars represent 15 ℓ. The bound ants that occupied the perimeter of the raft at reference time, t₀ = 0, are outlined in red and were traced through time. (F) The time-evolution of the edge binding rate, α, and bulk unbinding rate, δ, as a percentage per unit raft area are shown for two sets of experiments (squares for α and triangles for δ; red and black for two different experiments) along with the averaged results of 12 simulations (continuous black curves). Note that the initial drops in both α and δ for the simulation data occur since the raft was not initiated at steady state, whereas experimental data was only sampled at pseudo-steady state. (A,C,D,F) Experimental results are courtesy of Wagner, et al. (2021) [14]. All simulated rafts were initiated as circles and shape was allowed to evolve stochastically.

doi: https://doi.org/10.1371/journal.pcbi.1009869.g003