Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session A47: Focus Session: Physics of Behavior I |
Hide Abstracts |
Sponsoring Units: DBIO Chair: Greg Stephens, Vrije Universiteit Amsterdam & Okinawa Institute of Science and Technology Room: 217B |
Monday, March 2, 2015 8:00AM - 8:12AM |
A47.00001: ABSTRACT WITHDRAWN |
Monday, March 2, 2015 8:12AM - 8:24AM |
A47.00002: How to catch a falling fruit Andrew Marantan, Lakshminarayanan Mahadevan A variety of fish engage in complex hunting behaviors involving catching airborne prey falling to the surface of the water. In principle this requires that the fish develop internal models describing both the falling prey and its own motion relative to that prey. However learning such models is complicated by the fact that the fish must also account for noise in optical measurements and the refraction occurring at the air/water interface. Inspired by experimental observations, we describe how one such species (Brycon guatemalensis) might feasibly overcome these obstacles and learn a model accurate enough to catch falling fruit. Instead of learning a model for how the fruit falls and a model for how it moves in the water and a model accounting for refraction, we argue that the fish could instead learn one approximate linear model relating a set of measured inputs to a set of measured outputs valid in a limited domain of initial conditions. The fish could then make its control decisions based on the outcome predicted by this combined linear model. We also discuss how the fish can leverage neural transformations of raw data to learn a model with a larger domain of validity and yet more sensitive to noise due to nontrivial Jacobians arising from the neural transformations. [Preview Abstract] |
Monday, March 2, 2015 8:24AM - 8:36AM |
A47.00003: Growth behaviors of bacteria reveal the evolutionary significance of energy-efficiency Arijit Maitra, Ken Dill Microorganisms have evolved a mosaic of gene expression changes to adapt their growth behaviors to changing environmental conditions. The subset of genes coding for the protein translation machineries, the ribosomes, however display robust linear activities with growth rates. Such patterns are considered to be the source of growth itself. There is another robust growth law, observed by Monod in the 1940s, in which bacteria are able to scale their growth with food concentration before plateauing off to a constant value. To interlink these observed growth laws we derive an analytical network model that leverages metabolic data to capture how the cell manages its exchange of energy to support costly gene expression. The model explores the limits of energy allocation for function and reveals evolutionary principles. Among others, we find, in glucose medium the fastest growing \textit{E. coli} operate close to their maximum energy-efficiency. Optimization of energy efficiency provides a quantitative limit to how much energy is allocated for protein synthesis and it is determined by evolutionarily selected structural and biophysical constants. We conclude that energy efficiency has played a key role in bacterial evolution. [Preview Abstract] |
Monday, March 2, 2015 8:36AM - 8:48AM |
A47.00004: Migration of amoeba cells in an electric field Isabella Guido, Eberhard Bodenschatz Exogenous and endogenous electric fields play a role in cell physiology as a guiding mechanism for the orientation and migration of cells. Electrotaxis of living cells has been observed for several cell types, e.g. neurons, fibroblasts, leukocytes, neural crest cells, cancer cells. Dictyostelium discoideum (Dd), an intensively investigated chemotactic model organism, also exhibits a strong electrotactic behavior moving toward the cathode under the influence of electric fields. Here we report experiments on the effects of DC electric fields on the directional migration of Dd cells. We apply the electric field to cells seeded into microfluidic devices equipped with agar bridges to avoid any harmful effects of the electric field on the cells (ions formation, pH changes, etc.) and a constant flow to prevent the build-up of chemical gradient that elicits chemotaxis. Our results show that the cells linearly increase their speed over time when a constant electric field is applied for a prolonged duration (2 hours). This novel phenomenon cannot be attributed to mechanotaxis as the drag force of the electroosmotic flow is too small to produce shear forces that can reorient cells. It is independent of the cellular developmental stage and to our knowledge, it was not observed in chemotaxis. [Preview Abstract] |
Monday, March 2, 2015 8:48AM - 9:00AM |
A47.00005: Rhythmicity, recurrence, and recovery of flagellar beating Kirsty Wan, Raymond Goldstein The eukaryotic flagellum beats with apparently unfailing periodicity, yet responds rapidly to stimuli. Like the human heartbeat, flagellar oscillations are now known to be noisy. Using the unicellular alga \textit{Chlamydomonas reinhardtii}, we explore three aspects of nonuniform flagellar beating. We report the existence of rhythmicity, waveform noise peaking at transitions between power and recovery strokes, and fluctuations of interbeat intervals that are correlated and even recurrent, with memory extending to hundreds of beats. These features are altered qualitatively by physiological perturbations. Further, we quantify the recovery of periodic breaststroke beating from transient hydrodynamic forcing. These results will help constrain microscopic theories on the origins and regulation of flagellar beating. [Preview Abstract] |
Monday, March 2, 2015 9:00AM - 9:12AM |
A47.00006: Crosslink dynamics in a model of two filaments of actin under shear Arjan Boerma, Erik Van der Giessen, Stefanos Papanikolaou We seek to elucidate the dynamic mechanisms underlying the stress dependent effects of the cellular cytoskeleton, as they are observed in the storage and loss modulus as a function of frequency and cross-linker concentration. We report on the statistical behavior of the effects originating from cross-linker dynamics in the basic constituent of a cytoskeleton network: two mutually cross-linked filaments. We model each of the filaments and the cross-linkers in terms of elastic finite elements. Unbinding of individual cross-linkers takes place through a realistic constitutive model and re-binding may occur to maintain the average cross-linker density. Our approach provides a direct analysis of the athermal interplay of the elastic filament interactions with the dynamics of the cross-linking molecules. [Preview Abstract] |
Monday, March 2, 2015 9:12AM - 9:24AM |
A47.00007: Neuromechanics of crawling in \textit{D. melanogaster} larvae Cengiz Pehlevan, Paolo Paoletti, L. Mahadevan Nervous system, body and environment interact in non-trivial ways to generate locomotion and thence behavior in an organism. Here we present a minimal integrative mathematical model to describe the simple behavior of forward crawling in \textit{Drosophila} larvae. Our model couples the excitation-inhibition circuits in the nervous system to force production in the muscles and body movement in a frictional environment, which in turn leads to a proprioceptive signal that feeds back to the nervous system. Our results explain the basic observed phenomenology of crawling with or without proprioception, and elucidate the stabilizing role of proprioception in crawling with respect to external and internal perturbations. Our integrated approach allows us to make testable predictions on the effect of changing body-environment interactions on crawling, and serves as a substrate for the development of hierarchical models linking cellular processes to behavior. [Preview Abstract] |
Monday, March 2, 2015 9:24AM - 9:36AM |
A47.00008: Entropy measures of collective cell migration Ariadne Whitby, Simona Parrinello, Aldo Faisal Collective cell migration is a critical process during tissue formation and repair. To this end there is a need to develop tools to quantitatively measure the dynamics of collective cell migration obtained from microscopy data. Drawing on statistical physics we use entropy of velocity fields derived from dense optic flow to quantitatively measure collective migration. Using peripheral nerve repair after injury as experimental system, we study how Schwann cells, guided by fibroblasts, migrate in cord-like structures across the cut, paving a highway for neurons. This process of emergence of organised behaviour is key for successful repair, yet the emergence of leader cells and transition from a random to ordered state is not understood. We find fibroblasts induce correlated directionality in migrating Schwann cells as measured by a decrease in the entropy of motion vector. We show our method is robust with respect to image resolution in time and space, giving a principled assessment of how various molecular mechanisms affect macroscopic features of collective cell migration. Finally, the generality of our method allows us to process both simulated cell movement and microscopic data, enabling principled fitting and comparison of \emph{in silico} to \emph{in vitro}. [Preview Abstract] |
Monday, March 2, 2015 9:36AM - 9:48AM |
A47.00009: Sensory-motor system identification of active perception in ecologically valid environments William Abbott, Andreas Thomik, A. Aldo Faisal The brain is a dynamical system mapping sensory inputs to motor actions. This relationship has been widely characterised by reductionist controlled experiments. Here we present work moving out of the lab ``into the wild'' to capture, rather than constrain, sensory inputs and motor outputs, by recording 90\% of sensory inputs using head mounted eye-tracking, scene camera and microphone as well as recording 95\% of skeletal motor outputs by motion tracking 51 degrees of freedom in the body and a total of 40 degrees of freedom from the hands. We can thus begin to systematically characterise the perception-action loop through system identification. This enables use to evaluate classical relationships in ecologically valid settings and behaviours including 3 daily scenarios: breakfast in the kitchen, evening chores and activities and in-door ambulation . This level of data richness (97 DOF, 60Hz), coupled with the extensive recordings of natural perceptual and behavioural data (total $>$ 30 hrs, 10 subjects) enables us to answer general questions of how lab tasks and protocols will produce systematically different results from those found in daily life. [Preview Abstract] |
Monday, March 2, 2015 9:48AM - 10:00AM |
A47.00010: Animal and robot experiments to discover principles behind the evolution of a minimal locomotor apparatus for robust legged locomotion Benjamin McInroe, Henry Astley, Sandy Kawano, Richard Blob, Daniel I. Goldman In the evolutionary transition from an aquatic to a terrestrial environment, early walkers adapted to the challenges of locomotion on complex, flowable substrates (e.g. sand and mud). Our previous biological and robotic studies have demonstrated that locomotion on such substrates is sensitive to both limb morphology and kinematics. Although reconstructions of early vertebrate skeletal morphologies exist, the kinematic strategies required for successful locomotion by these organisms have not yet been explored. To gain insight into how early walkers contended with complex substrates, we developed a robotic model with appendage morphology inspired by a model analog organism, the mudskipper. We tested mudskippers and the robot on different substrates, including rigid ground and dry granular media, varying incline angle. The mudskippers moved effectively on all level substrates using a fin-driven gait. But as incline angle increased, the animals used their tails in concert with their fins to generate propulsion. Adding an actuated tail to the robot improved robustness, making possible locomotion on otherwise inaccessible inclines. With these discoveries, we are elucidating a minimal template that may have allowed the early walkers to adapt to locomotion on land. [Preview Abstract] |
Monday, March 2, 2015 10:00AM - 10:12AM |
A47.00011: Evolution of foraging behavior in Drosophilid larvae Marta Rivera-Alba, Mayank Kabra, Kristin Branson, Christen Mirth Drosophilids, like other insects, go through a larval phase before metamorphosing into adults. Larvae increase their body weight by several orders of magnitude in a few days. We therefore hypothesized that foraging behavior is under strong evolutionary pressure to best fit the larval environment. To test our hypothesis we used a multidisciplinary approach to analyze foraging behavior across species and larval stages. First, we recorded several videos of larvae foraging for each of 47 Drosophilid species. Then, using a supervised machine learning approach, we automatically annotated the video collection for the foraging sub-behaviors, including crawling, turning, head casting or burrowing. We also computed over 100 features to describe the posture and dynamics of each animal in each video frame. From these data, we fit models to the behavior of each species. The models each had the same parametric form, but differed in the exact parameters. By simulating larva behavior in virtual arenas we can infer which properties of the environments are better for each species. Comparisons between these inferred environments and the actual environments where these animals live will give us a deeper understanding about the evolution of foraging behavior in Drosophilid larvae. [Preview Abstract] |
Monday, March 2, 2015 10:12AM - 10:24AM |
A47.00012: Collective workload organization in confined excavation of granular media Daria Monaenkova, Vadim Linevich, Michael A. Goodisman, Daniel I. Goldman Many social insects collectively construct large nests in complex substrates; such structures are often composed of narrow tunnels. The benefits of collective construction, including reduced construction costs per worker come with challenges of navigation in crowded, confined spaces. Here we study the workforce organization of groups of {\it S. invicta} fire ants creating tunnels in wet granular media. We monitor the activity levels of marked (painted) workers--defined as a number of tunnel visits over 12 hours-- during initiation of tunnels. The activity levels are described by a Lorenz curve with a Gini coefficient of $\sim 0.7$ indicating that a majority of the excavation is performed by a minority of workers. We hypothesize that this workload distribution is beneficial for excavation in crowded conditions, and use a 2D cellular automata (CA) model to reproduce behaviors of the excavating ants. CA simulations reveal that tunnel construction rates decrease in groups of equally active animals compared to groups with the natural workload distribution. We use predictions of the CA model to organize collective excavation of granular material by teams of digging robots, and use the robots to test hypotheses of crowded excavation in the physical world. [Preview Abstract] |
Monday, March 2, 2015 10:24AM - 11:00AM |
A47.00013: Nociception and escape behavior in planarians Invited Speaker: Eva-Maria Schoetz Collins Planarians are famous and widely studied for their regenerative capabilities. When a moving planarian is cut through the middle, the resulting head and tail pieces instantaneously retract and exhibit a characteristic escape response that differs from normal locomotion. In asexual animals, a similar reaction is observed when the planarian undergoes fission, suggesting that reproduction through self-tearing is a rather traumatic event for the animal. Using a multiscale approach, we unravel the dynamics, mechanics, and functional aspects of the planarian escape response. This musculature-driven gait was found to be a dominating response that supersedes the urge to feed or reproduce and quantitatively differs from other modes of planarian locomotion (gliding, peristalsis). We show that this escape gait constitutes the animal's pain response mediated by TRP like receptors and the neurotransmitter histamine, and that it can be induced through adverse thermal, mechanical, electrical or chemical stimuli. Ultimately, we will examine the neuronal subpopulations involved in mediating escape reflexes in planarians and how they are functionally restored during regeneration, thereby gaining mechanistic insight into the neuronal circuits required for specific behaviors. [Preview Abstract] |
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