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Whirligig beetles as corralled active Brownian particles.

Authors
  • Devereux, Harvey L1, 2
  • Twomey, Colin R3
  • Turner, Matthew S4, 5, 6
  • Thutupalli, Shashi2, 7
  • 1 Department of Mathematics, University of Warwick, Coventry CV4 7AL, UK.
  • 2 Simons Center for the Study of Living Machines, National Centre for Biological Sciences, Tata Institute for Fundamental Research, Bangalore 560065, India. , (India)
  • 3 Department of Biology, and Mind Center for Outreach, Research and Education, University of Pennsylvania, Philadelphia, PA, USA.
  • 4 Department of Physics, University of Warwick, Coventry CV4 7AL, UK.
  • 5 Centre for Complexity Science, University of Warwick, Coventry CV4 7AL, UK.
  • 6 Department of Chemical Engineering, Kyoto University, Kyoto 615-8510, Japan. , (Japan)
  • 7 International Centre for Theoretical Sciences, Tata Institute for Fundamental Research, Bangalore 560089, India. , (India)
Type
Published Article
Journal
Journal of The Royal Society Interface
Publisher
The Royal Society
Publication Date
Apr 01, 2021
Volume
18
Issue
177
Pages
20210114–20210114
Identifiers
DOI: 10.1098/rsif.2021.0114
PMID: 33849331
Source
Medline
Keywords
Language
English
License
Unknown

Abstract

We study the collective dynamics of groups of whirligig beetles Dineutus discolor (Coleoptera: Gyrinidae) swimming freely on the surface of water. We extract individual trajectories for each beetle, including positions and orientations, and use this to discover (i) a density-dependent speed scaling like v ∼ ρ-ν with ν ≈ 0.4 over two orders of magnitude in density (ii) an inertial delay for velocity alignment of approximately 13 ms and (iii) coexisting high and low-density phases, consistent with motility-induced phase separation (MIPS). We modify a standard active Brownian particle (ABP) model to a corralled ABP (CABP) model that functions in open space by incorporating a density-dependent reorientation of the beetles, towards the cluster. We use our new model to test our hypothesis that an motility-induced phase separation (MIPS) (or a MIPS like effect) can explain the co-occurrence of high- and low-density phases we see in our data. The fitted model then successfully recovers a MIPS-like condensed phase for N = 200 and the absence of such a phase for smaller group sizes N = 50, 100.

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