Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session L5: Physics of Behavior |
Hide Abstracts |
Sponsoring Units: DBIO Chair: Greg Stephens, Vrije Universiteit Amsterdam Room: 264 |
Wednesday, March 15, 2017 11:15AM - 11:27AM |
L5.00001: Ising model for collective decision making during group motion Itai Pinkoviezky, Nir Gov, Iain Couzin Collective decision making is a key feature during natural motion of animal groups and is also crucial for human groups. This phenomenon can be exemplified by the scenario of two subgroups that hold conflicting preferred directions of motion. The constraint of group cohesion drives the motion either towards a compromise or towards one of the preferred targets. The transition between compromise and decision has been found in simulations of flock models, but the nature of this transition is not well understood. We present a minimal spin model for this system where we interpret the spin-spin interaction as a social force. This model exhibits both first and second order transitions. The group motion changes from size-dependent diffusion at high temperatures to run-and-tumble motion below the critical temperature. In the presence of minority and majority subgroups, we find that there is a trade-off between the speed of reaching a target and the accuracy. We then compare the results of the spin model to detailed simulations of a flock model, and find overall very similar dynamics, with the role of the temperature taken by the inverse of the number of uninformed individuals. [Preview Abstract] |
Wednesday, March 15, 2017 11:27AM - 11:39AM |
L5.00002: Mechanical adaptation in adhesive bee swarms Orit Peleg, Jacob Peters, Mary Salcedo, Lakshminarayanan Mahadevan Honeybees often form swarms [1] that take on an inverted cone shape where the bees hold on to each other, and form a large structure that can be hundreds of times the size of a single organism. The mechanism by which a multitude of bees work together, without an overseer, to create a stable structure that defies static gravity and dynamic stimuli (e.g. wind), remains elusive. To test the role of mechanical cues in the swarm morphogenesis, we developed an experimental setup in which mechanical perturbations were applied to a swarm. In response, the bees tuned the aspect ratio of the swarm dynamically toward a wider, more stable, cone. Interestingly, the evolution of the contact area collapsed onto a master curve when plotted vs. number of perturbation events (rather than time), highlighting a possible mechanism by which bees are able to respond to events of sharp force. Indeed, agent-based simulations where individual bees are capable of sensing local mechanical stresses, and respond by changing the global shape of the swarm, are in qualitative agreement with the experimental results. Altogether, our results show how an active, functional structure can respond adaptively to dynamic mechanical loading and share the load by moving into the breach, which might be termed ``Mechanical Altruism''. [1] T. D. Seeley, Honeybee Democracy, Princeton University Press, 2010 [Preview Abstract] |
Wednesday, March 15, 2017 11:39AM - 11:51AM |
L5.00003: Prey and mound disassembly, manipulation and transport by fire ant collectives Bahnisikha Dutta, Daria Monaenkova, Michael A. Goodisman, Daniel Goldman Fire ants inhabit subterranean nests covered by a hemispherical mound of soil permeated by narrow ($\sim $1 body length diameter) tunnels. Fire ants can use their mound for long-term food storage [Gayahan $\& $Tschinkel, J. Insect Sci.,2008]. Since mound tunnels are narrow, we expect that in addition to prey manipulation, mound reconfiguration could also be an important aspect of the food storage strategy. Ant colonies collected from wild were allowed to build nests in containers filled with clay soil in the laboratory. These colonies were offered diverse prey embedded with lead markers, including mealworms, crickets and shrimp. Ant-prey-soil interactions on the nest surface were recorded using overhead video and subsurface using x-ray imaging. Individual ants involved in prey storage exhibited three distinct behaviors: prey maneuvering, prey dissection and mound reconfiguration. Small prey (e.g. mealworms) were collectively carried intact into the mound through a tunnel, and then disassembled within the mound. Larger prey (e.g. shrimp) were dismantled into small pieces above the surface and carried to mound tunnels. The bodies of hard medium-sized prey (e.g. crickets) were buried after limb removal and then disassembled and moved into tunnels. Soil reconfiguration occurred in all cases. [Preview Abstract] |
Wednesday, March 15, 2017 11:51AM - 12:03PM |
L5.00004: Engineering emergent multicellular behavior through synthetic adhesion David Glass, Ingmar Riedel-Kruse In over a decade, synthetic biology has developed increasingly robust gene networks within single cells, but constructed very few systems that demonstrate multicellular spatio-temporal dynamics. We are filling this gap in synthetic biology's toolbox by developing an E. coli self-assembly platform based on modular cell-cell adhesion. We developed a system in which adhesive selectivity is provided by a library of outer membrane-displayed peptides with intra-library specificities, while affinity is provided by consistent expression across the entire library. We further provide a biophysical model to help understand the parameter regimes in which this tool can be used to self-assemble into cellular clusters, filaments, or meshes. The combined platform will enable future development of synthetic multicellular systems for use in consortia-based metabolic engineering, in living materials, and in controlled study of minimal multicellular systems. [Preview Abstract] |
Wednesday, March 15, 2017 12:03PM - 12:15PM |
L5.00005: Quantifying the group specificity of animal vocalizations through relative entropies Sarah Hallerberg, Marc Timme, Kurt Hammerschmidt, Heike Vester Recordings of animal vocalization can lack of important information about sender and context, in particular in the increasing number of bio-acoustic monitorings and in studies on marine mammals. Here, we develop a framework to estimate group specificity without specific sender information. We introduce and apply the bag-of-calls-and-coefficients approach (BOCCA) to study ensembles of cepstral coefficients composed from vocalization signals recorded from a given animal group. Comparing distributions of such ensembles of coefficients by computing relative entropies reveals group specific differences. We illustrate the ensemble-based method by showing that differences of ensembles of calls within social groups of pilot whales (Globicephala melas) are significantly lower than inter-group differences. [Preview Abstract] |
Wednesday, March 15, 2017 12:15PM - 12:27PM |
L5.00006: Capturing the continuous complexity of natural behavior in the movement of C. elegans Tosif Ahamed, Greg Stephens Progress in imaging and machine vision has made it possible to quantify animal movement at unprecedented spatiotemporal scales and resulting analyses have suggested a picture of behavior composed of discrete, stereotyped motifs and transitions between them. However this description is only an approximation to more fundamental continuous dynamics and ignores the variability within each motif. Here, we combine video tracking of the nematode C. elegans with concepts from nonlinear dynamics to reconstruct the phase space of the worm’s locomotion. We show that the dynamics lie on a 6D attractor, which is globally composed of three sets of cyclic trajectories that form the animal's most stereotyped behaviors: forward, backward and turning locomotion. In contrast to such global stereotypy, we also observe substantial local variability, which is reflected in positive Lyapunov exponents for each set of cycles. Across the full attractor we find that the Lyapunov spectrum is symmetric about a small negative value, suggesting a dissipative Hamiltonian structure in the underlying dynamics. Finally, we estimate the Kolmogorov-Sinai entropy through the sum of the positive exponents to show that local variability decreases as the animals adapt from a diffusive to a ballistic search strategy. [Preview Abstract] |
Wednesday, March 15, 2017 12:27PM - 12:39PM |
L5.00007: Exploring a strongly non-Markovian behavior Vasyl Alba, Gordon Berman, William Bialek, Joshua Shaevitz Is there some simplicity or universality underlying the complexities of natural animal behavior?~Using the walking fruit fly as a model system, we have shown that unconstrained behaviors can be categorized into roughly one hundred discrete states, which all individuals from a single species visit repeatedly. In each state, the fly executes stereotyped movements, and the transitions between states are organized hierarchically. The sequences of states, however, are strongly non-Markovian: correlations persist for orders of magnitude longer than expected from the state-to-state transition probabilities, and there are hints of power law decay. But with 100 states, further analysis is difficult. Here we develop a generalization of the information bottleneck method to compress these states into a more compact description that preserves as much of the temporal correlations as possible. We find that, even on compressing down to just two states, this coarse grained description of behavior captures the long ranged correlations. Power law decays are clearer in this reduced representation, which opens the way for more quantitative analysis. [Preview Abstract] |
Wednesday, March 15, 2017 12:39PM - 12:51PM |
L5.00008: Mechanical diffraction in a sand-specialist snake Perrin E Schiebel, Jennifer M Rieser, Alex M Hubbard, Lillian Chen, Daniel I Goldman Limbless locomotors such as snakes move by pressing the trunk against terrain heterogeneities. Our laboratory studies of the desert-dwelling Mojave Shovel-nosed snake (\textit{C. occipitalis}, $\sim$40cm long, N=9) reveal that these animals use a stereotyped sinusoidal traveling wave of curvature. However, this snake also encounters rigid obstacles in its natural environment, and the tradeoff between using a cyclic, shape controlled gait versus one which changes shape in response to the terrain is not well understood. We challenged individuals to move across a model deformable substrate (carpet) through a row of 6.4 mm diameter force-sensitive pegs, a model of obstacles such as grass, oriented perpendicular to the direction of motion. Instead of forward-directed reaction forces, reaction forces generated by the pegs were more often perpendicular to the direction of motion. Distributions of post-peg travel angles displayed preferred directions revealing a diffraction-like pattern with a central peak at zero and symmetric peaks at \pm19\pm3 $^{\circ}$ and 41\pm 5 $^{\circ}$. We observed similar dynamics in a robotic snake using shape-based control. This suggests that this sand-specialist snake adheres to its preferred waveform as opposed to changing in response to heterogeneity. [Preview Abstract] |
Wednesday, March 15, 2017 12:51PM - 1:03PM |
L5.00009: Testability of evolutionary game dynamics based on experimental economics data Yijia Wang, Xiaojie Chen, Zhijian Wang In order to better understand the dynamic processes of a real game system, we need an appropriate dynamics model, so to evaluate the validity of a model is not a trivial task. Here, we demonstrate an approach, considering the dynamical macroscope patterns of angular momentum and speed as the measurement variables, to evaluate the validity of various dynamics models. Using the data in real time Rock-Paper-Scissors (RPS) games experiments, we obtain the experimental dynamic patterns, and then derive the related theoretical dynamic patterns from a series of typical dynamics models respectively. By testing the goodness-of-fit between the experimental and theoretical patterns, the validity of the models can be evaluated. One of the results in our study case is that, among all the nonparametric models tested, the best-known Replicator dynamics model performs almost worst, while the Projection dynamics model performs best. Besides providing new empirical macroscope patterns of social dynamics, we demonstrate that the approach can be an effective and rigorous tool to test game dynamics models. [Preview Abstract] |
Wednesday, March 15, 2017 1:03PM - 1:15PM |
L5.00010: Division of Labor in the Absence of Task-Switching Costs Shane Meyer, Sonya Bahar The evolution of division of labor is a question of critical importance in biology. Mathematical models have consistently shown that some sort of tradeoff \quad is required in order for specialization to evolve. In some models, the tradeoff is an explicit cost of \textit{task-switching}, where it is easier to continue one task than it is to begin a new one. We have developed an agent-based model to investigate other forms of tradeoffs which could naturally lead to specialization. The model includes two populations competing for one essential resource. Agents in the model have two traits which influence their probabilities to forage for resource or socialize with another agent, allowing sharing of resource to occur. Results from the model show that restricting agents to perform one task at a time, along with risks associated with foraging for essential resources in the environment, can lead to a population where some members evolve to avoid foraging. This demonstrates that some degree of division of labor can indeed evolve in the absence of task-switching costs. [Preview Abstract] |
Wednesday, March 15, 2017 1:15PM - 1:27PM |
L5.00011: How Market Structure Drives Commodity Prices Bin Li, K. Y. Michael Wong, Amos H. M. Chan, Tsz Yan So, Hermanni Heimonen, David Saad To understand how market structure drives commodity price trends with respect to resource availability we introduce an agent-based model, in which agents set their prices to maximize profit. At steady state the market self-organizes into three groups: excess producers, consumers and balanced agents. When resources are scarce prices rise sharply below a turning point marking the disappearance of excess producers. By introducing an elasticity parameter to mitigate noise and long-term changes in commodities data, we confirm the trend of rising prices, provide evidence for turning points, and indicate yield points for less essential commodities. [Preview Abstract] |
Wednesday, March 15, 2017 1:27PM - 1:39PM |
L5.00012: Spectra of Adjacency Matrices in Networks of Extreme Introverts and Extroverts Kevin E. Bassler, Mohammadmehdi Ezzatabadipour, R.K.P. Zia Many interesting properties were discovered in recent studies of preferred degree networks, suitable for describing social behavior of individuals who tend to prefer a certain number of contacts. In an extreme version (coined the XIE model), introverts always cut links while extroverts always add them. While the intra-group links are static, the cross-links are dynamic and lead to an ensemble of bipartite graphs, with extraordinary correlations between elements of the incidence matrix: nij In the steady state, this system can be regarded as one in thermal equilibrium with long-ranged ``interactions” between the $n_{ij}$’s, and displays an extreme Thouless effect [details in JSTAT P07013, 2015]. Here, we report simulation studies of a different perspective of networks, namely, the spectra associated with this ensemble of adjacency matrices $\{a_{ij} \}$. As a baseline, we first consider the spectra associated with a simple random (Erd\H{o}s-R\'{e}nyi) ensemble of bipartite graphs, where simulation results can be understood analytically. [Preview Abstract] |
Wednesday, March 15, 2017 1:39PM - 1:51PM |
L5.00013: Non-trivial Correlations in a Model of Extreme Introverts Extroverts Mohammadmehdi Ezzatabadipour, Kevin E. Bassler, R.K.P. Zia Recent studies showed that the XIE model of extreme introverts and extroverts display remarkable collective properties (JSTAT P07013, 2015). A configuration of this evolving stochastic system, the cross-links between the two groups, is uniquely specified by an incidence matrix: $n_{ij} (=0,1)$. Regarding this system as an Ising lattice gas, the stationary distribution was found exactly and can be interpreted as $exp(-H)$, with long-range, multi- spin interactions in $H$. Though extraordinary \underline{correlations} between the $n$’s can be expected, the underlying permutation symmetries obscure our intuition. Using computer simulations, we study these correlations in detail, contrasting them with those in random ensembles of bipartite graphs. One surprise is that links connecting two distinct pairs of introverts and extroverts are anti-correlated. We also measure degree distributions of the two groups, as well as the distribution of the total number of cross-links, and relate them to various correlations, finding excellent agreement between simulations and theory. Finally, a self-consistent mean field approach is formulated, which can predict the distributions and so, the correlations. [Preview Abstract] |
Wednesday, March 15, 2017 1:51PM - 2:03PM |
L5.00014: The Variations of Modularity in Patients' Heart Rates during the Spontaneous Breathing Trial Liang Niestemski, Timothy Buchman, Michael Deem The spontaneous breathing trial (SBT) is a frequent procedure in critical care during which mechanical ventilation is briefly suspended while the patient breathes for a time without that support. We study the variations of the patients' Heart rates before, during, and after the SBT. Time dependent covariance matrices are constructed from Heart rates data and modularity of such matrices are investigated. The results show that environmental pressure induces high modularity during SBT. [Preview Abstract] |
Wednesday, March 15, 2017 2:03PM - 2:15PM |
L5.00015: Plant root and shoot dynamics during subsurface obstacle interaction Nathaniel Conn, Jeffrey Aguilar, Philip Benfey, Daniel Goldman As roots grow, they must navigate complex underground environments to anchor and retrieve water and nutrients. From gravity sensing at the root tip to pressure sensing along the tip and elongation zone, the complex mechanosensory feedback system of the root allows it to bend towards greater depths and avoid obstacles of high impedance by asymmetrically suppressing cell elongation. Here we investigate the mechanical and physiological responses of roots to rigid obstacles. We grow Maize, \textit{Zea mays}, plants in quasi-2D glass containers (22cm x 17cm x 1.4cm) filled with photoelastic gel and observe that, regardless of obstacle interaction, smaller roots branch off the primary root when the upward growing shoot (which contains the first leaf) reaches an average length of 40 mm, coinciding with when the first leaf emerges. However, prior to branching, contacts with obstacles result in reduced root growth rates. The growth rate of the root relative to the shoot is sensitive to the angle of the obstacle surface, whereby the relative root growth is greatest for horizontally oriented surfaces. We posit that root growth is prioritized when horizontal obstacles are encountered to ensure anchoring and access to nutrients during later stages of development. [Preview Abstract] |
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