Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session T11: Collective Behaviors in Biology II |
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Sponsoring Units: DBIO Chair: Alice Pyne, University of Sheffield Room: Room 203 |
Thursday, March 9, 2023 11:30AM - 11:42AM |
T11.00001: Sled Dogs as Tethered Active Agents: Part 1 Benjamin Seleb, Matthew S Bull, Saad Bhamla
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Thursday, March 9, 2023 11:42AM - 11:54AM |
T11.00002: Sled dogs as tethered active agents: Part 2 Matthew S Bull, Benjamin Seleb, Saad Bhamla Teams of sled dogs balance an individual's perception, decision making, and physical capabilities with the collective performance of the whole. To do well, this active network must maintain collective stability while simultaneously enabling sufficient agility to respond to a dynamic environment and attempts to control the team by a driver. Unlike many self-organizing systems, these teams are assembled in a manner which reflects and embraces the underlying diversity of the team members in service of competition performance. In this study, we complement a suite of multiscale fieldwork measurements of sled dog teams (see part 1) during training to understand how dog teams balance responsive agility with stability using harness physics, cyclic gaits, and simplified perceptual decision making rules. Our work reconciles low dimensional descriptions of dog behavior into the emergent dynamics of the team. |
Thursday, March 9, 2023 11:54AM - 12:06PM |
T11.00003: Strong Casimir-like Forces in Flocking Active Matter Giuseppe Fava Flocking – the collective motion exhibited by certain active matter (AM) systems – is a ubiquitous phenomenon, observed in a wide array of different living systems and on an even wider range of scales. |
Thursday, March 9, 2023 12:06PM - 12:18PM |
T11.00004: Fish Shoals are Viscoelastic Materials Pasha A Tabatabai, Gabriel Kuntz, Mitchell Rask A fundamental difference between living and non-living systems is that constituents within living systems consume energy. In the natural world, this leads to fantastic patterns and collective behaviors across many lengthscales. This talk focuses on describing these active systems as amorphous non-equilibrium materials by investigating laboratory schools of fish. Using imaging and image analysis techniques, we investigate the structure and rearrangements of fish within a school as a means to probe the mechanical properties of a living material. |
Thursday, March 9, 2023 12:18PM - 12:30PM |
T11.00005: Fluid circulation driven by collectively organized metachronal waves in swimming T. aceti nematodes Anton Peshkov, Alice C Quillen, Brato Chakrabarti Recent experiments have shown that the nematode T. aceti can assemble into collectively undulating groups at the edge of fluid drops. This coordinated state consists of metachronal waves that drive fluid circulation inside the drop. We experimentally measure the properties of these flows and compare them to an analytical model. For the latter, we develop a quasi two-dimensional hydrodynamics model using the Stokes flow approximation. The periodic motion of the nematodes constitutes our moving boundary condition that drives the flow. Our model suggests that large amplitude excursions of the nematodes tails produce fluid circulation. We discuss the constraints on containers that would enhance fluid motion, which could be used in the future design of on-demand flow generating systems. |
Thursday, March 9, 2023 12:30PM - 12:42PM |
T11.00006: Collective behaviors of elastic filaments undulating in close proximity Narina Jung, Won Kyu Kim, Changbong Hyeon In order to investigate the collective behaviors of a suspension of active filaments in the limit of a non-dilute regime, we study the interactions relevant to the closely spaced multiple elastic filaments slowly swimming by undulation in a confined viscous fluid. The hydrodynamics and steric interactions between two filaments with an aspect ratio, a/L, critically depend on the separation distance d. We focus on the conditions for the formation of meta-chronal waves of multiple filaments aligned at a wall focusing on the regime of a d L. We consider various tilting angles that possibly break the symmetry in the governing equation and their effects on propulsion efficiency. We quantify the relative importance of the hydrodynamics and the steric interactions to the formation of metachronal waves of undulating bodies as a function of the average separation distance in the suspension. |
Thursday, March 9, 2023 12:42PM - 12:54PM |
T11.00007: Ecological context shapes collective turns and velocity correlations in jackdaw flocks Hangjian Ling, Nicholas T Ouellette, Alex Thornton, Guillam E Mclvor, Daniel O O’Coin Recently, ecological context has been shown to have a profound impact on the collective motion of wild animals. Animals in different contexts can use different inter-individual interaction rules, and consequently produce different group-level properties. In this talk, we report that ecological context can also influent collective turns and velocity correlations for flocks of jackdaws (Corvus monedula). We used a three-dimensional imaging system to track the movement of jackdaws in two different contexts: transit flocks where birds travel from one location to another, and mobbing flocks where birds respond to a predatory stimulus. We found that context may alter where turns were initiated in the flocks: for transit flocks in the absence of predators, initiators were located either at the front or at the back of the flocks, but for mobbing flocks with a fixed ground-based predator, they were always located at the front. In addition, we found that the correlation length of velocity was independent of the group density for transit flocks, but increased with increasing the group density in mobbing flocks. This result confirms a previous observation that birds obey topological interactions in transit flocks, but switch to metric interactions in mobbing flocks. Our results highlight the importance of ecological context when studying collective animal behaviour. |
Thursday, March 9, 2023 12:54PM - 1:06PM |
T11.00008: Global coordination using local information in fire ant pontoon bridges Noah Egan, Haolin Zeng, Ram Avinery, Shengkai Li, Hosain Bagheri, Takao Sasaki, Daniel I Goldman Fire ants (Solenopsis invicta) can collectively entangle to create free-floating rafts which allow the colony to survive upon nest flooding. Here we demonstrate that they can also create adaptable structures which allow them to forage across a water surface. Laboratory experiments using sub-colonies of 8000 fire ants demonstrate that when the ants detect food in the center of a 14 cm diameter bowl filled with water, they self-assemble into a floating pontoon bridge consisting of approximately 500 ants to reach the food. Multiple proto-bridges initiate from the boundary; the ants add to proto-bridges by directly entering the water and/or using the water meniscus at the bowl rim to propel themselves into the water. Over time, most proto-bridges retract and a single final bridge forms, suggesting global coordination. Our agent-based model of the system suggests that the tendency for ants to join proto-bridges more often in areas with stronger food scent is sufficient for them to form a single bridge. This suggests ants’ ability to build a single bridge should be sensitive to environmental conditions. The model prediction that ants form multiple bridges in a bowl with nonuniform distance between the food and rim was verified in experiments, thus giving insights into how collectives can effectively coordinate over long distances using only local information to create adaptable functional structures. |
Thursday, March 9, 2023 1:06PM - 1:18PM |
T11.00009: Collective Motion of Proteus mirabilis Swarmer Cells Emma Dawson, Minsu Kim For surface attached bacteria, it’s all about location, location, location. Cooperative swarming is one strategy that allows cells to work together to expand their colony’s boundary over a surface they could not individually traverse, unlocking new territory and additional nutrients. Proteus mirabilis is a highly effective swarmer, best known for its counterintuitive swarming strategy. Rather than continuously swarming, P. mirabilis colonies alternate between phases of swarming and consolidation, generating a distinctive bullseye pattern. Systems such as chemotaxis or cellular clocks can generate bullseye patterns, but do not explain the swarming cycle of P. mirabilis, so we examine the collective motion of swarmer cells to elucidate the role of physical mechanisms in their pattern formation. Using a “precocious” swarming mutant, which lacks important regulation of the swarming cycle and swarms continuously, we are able to access a steady-state regime of swarming not seen in wild type colonies. We aim to model the collective motion of swarmer cells in the absence of regulation in the precocious mutant in order to understand how wild type regulation of the swarming cycle exploits the collective dynamics of swarmer cells to swarm so effectively. |
Thursday, March 9, 2023 1:18PM - 1:30PM |
T11.00010: Three-Dimensional Characterization of Surface Wave Behavior in Dense Colonies of M. xanthus Aaron R Bourque, Joshua W Shaevitz One of the characteristic collective phenomena displayed by the social bacterium Myxococcus xanthus is its ability to self-organize into wave-like structures termed ripples. Ripples occur in both developmental and predatory phases of its life cycle, where a colony of M. xanthus is densely packed and comprised of multiple cell layers. In this work, we characterize the properties of rippling in three-dimensions. Using a surface profilometer, we demonstrate that these waves span 6 to 20 cell layers in height with a characteristic wavelength that is dependent on the stiffness of a hydrogel substrate. We find coexistence of traveling waves that move away from the colony and standing waves within denser regions of the colony. Furthermore, we use spinning-disk confocal microscopy and sparse cell labeling to understand individual cell motility and ordering within these structures. We find that the colonies are able to maintain nematic order across cell layers and produce flows with speeds that exceed those of lone cells. |
Thursday, March 9, 2023 1:30PM - 1:42PM |
T11.00011: Morphogenetic process of a composite structure driven by contractile cells Donghyun Yim, Youngmin Jo, Pilnam Kim, Taeyoon Kim In epithelial morphogenesis, fibroblast cells play a central role in shaping a tissue into a mature form. Nevertheless, fibroblast has been neglected in most of the previous studies designed to investigate the morphogenesis. They have focused on the epithelium itself without consideration of interactions between fibroblast and epithelial tissue. We developed a tissue-equivalent system in vitro containing fibroblast cells within the collagen gel stacked with a collagen vitrigel membrane (CVM) and an epithelium in series. As a result, we observed that fibroblast cells fold an epithelial layer, which guides cell migration and is accompanied by fibrous alignment across cells. Concurrently, we developed an agent-based model to mimic the experimental system. In the model, a collagen matrix and the CVM were individually simplified into a fibrous matrix and a stiff layer adhesively coupled to each other. fibroblast cells were coarse-grained into spherical contractile entities capable of migrating, located within the fibrous matrix and right beneath the stiff layer. Cells pull surrounding fibers, leading to cell migration, matrix remodeling characterized by fiber alignment, and CVM folding. These reciprocal events are consistent with experimental results. Our research broadens knowledge about the role of fibroblast in tissue morphogenesis. |
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