Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session Z04: Phase Transitions in Evolutionary DynamicsFocus Recordings Available
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Sponsoring Units: DBIO GSNP DCOMP Chair: Justin Kinney, Cold Spring Harbor Laboratory Room: McCormick Place W-176C |
Friday, March 18, 2022 11:30AM - 12:06PM |
Z04.00001: Phase Transitions in Bacterial Populations Invited Speaker: R. Fredrik Inglis Phase transitions have been observed in a number of different biological systems and processes from bird flocks to neuronal firing. Recently, we have identified non-equilibrium phase transitions in microbial populations undergoing population extinction in response to specific environmental stressors such as temperature and antibiotics. These observed phase transitions during population collapse broadly correspond to previous computational models of evolutionary dynamics. Surprisingly, in our experiments there was a diverse pattern of population collapse within and between different classes of antibiotics with no obvious explanation for this difference. Even within classes of chemically related antibiotics some exhibit critical phase transition like behavior with sharp declines in growth and high standard deviations between bacterial populationsm, whereas others show much more gradual declines with very little difference between populations. Preliminary evidence from our lab suggests that these differences in phase-transition behavior may be in part driven by resistance evolution. We are currently using experimental evolution and next generation sequencing to investigate if the frequency and spectrum of possible resistance mutations determine the emergence of critical phase transitions during antibiotic treatment. This work will not only inform how and when antibiotic resistance mutations are likely to evolve but will more broadly investigate evolutionary rescue during critical phase transition population collapse. |
Friday, March 18, 2022 12:06PM - 12:42PM |
Z04.00002: Dynamics, stability, and robustness of minimal-change trajectories to increased multicellular size Invited Speaker: Thomas C Day The evolution of large organismal size is fundamentally important for multicellularity, creating new ecological niches and opportunities for the evolution of increased biological complexity. Yet little is known about how large size evolves, particularly in nascent multicellular organisms that lack genetically-regulated multicellular development. Here we examine how novel biophysical drivers of macroscopic multicellularity arise, including both the minimal requirements which drive novel biophysical adaptation and the dynamics of their emergence, using a combination of experiments and simulations. In a long-term evolutionary experiment, we observed multiple independent lines of multicellular snowflake yeast evolve macroscopic size rapidly, becoming 20,000 times larger and 10,000 times more physically tough over a span of 600 days. They accomplished this through sustained biophysical adaptation, evolving a novel trait, branch entanglement, so that groups of cells stay together after bond fracture. We developed simulations to interrogate the minimal changes that can be made to cellular and growth morphologies to facilitate branch entanglement. We find that cellular elongation, a trait observed in all lines of multicellular yeast experimental evolution, provides a robust and easy mechanism to delay the onset of bond fracture such that branch entanglement is more likely. Our simulations and experiments show that the emergent properties of simple multicellular groups can drive sustained biophysical adaptation, an early step in the evolution of increasingly complex organisms. In future work, we will continue to investigate the effects of other physical changes that may facilitate branch entanglement, including increasing bond strength, decreasing cell stiffness, or increasing the budding angle for more severe angles between parent and child cells. |
Friday, March 18, 2022 12:42PM - 12:54PM |
Z04.00003: Stable coexistence through dynamic adaptation of a shared resource Zachary L Jackson, BingKan Xue We study a system of self-replicating components that interact with a shared resource. The competition between the components would lead to a phase where only one of them dominates, depending on their interaction strengths with the resource. However, we show that a resource that has a dynamic internal structure can tune the effective interaction strengths and thus stabilize the system in a new coexistence phase. As a case study, we analyze an ecological system with exploitative competition between two predators feeding on a single prey. We consider a scenario where the prey diversifies into two phenotypes. If the ratio of the phenotypes is constant, then one of the predators is excluded. But if the relative abundance of the phenotypes adapts dynamically, then both predators can coexist, in some cases even if they could not persist on their own. The prey may benefit from diversification by spreading the detrimental effect of predation between two consumers, rather than being strongly affected by one. |
Friday, March 18, 2022 12:54PM - 1:06PM |
Z04.00004: Phase transitions, hysteresis and memory in microbial ecologies Antun Skanata, Edo Kussell Studies of isolated populations have provided general principles by which organisms adapt to environmental change. Molecular mechanisms are subject to evolutionary pressures to operate in changing environments, but also to distinct pressures arising from competitions within larger communities and in more complex ecologies. Therefore, selection forces can occur at different scales spanning from single populations to large ecological structures. While the dynamics at the population level are well studied, little is known how the molecular details benefit from pressures at the ecological level. |
Friday, March 18, 2022 1:06PM - 1:18PM |
Z04.00005: In Search of Universality in the Short-Time Dynamics of Systems of Coupled Ecological Oscillators Shadi Esmaeili-Wellman, Alan Hastings, Karen Abbott, Jonathan L Machta, Vahini Reddy Nareddy Synchronization is a widespread phenomenon observed in many oscillatory ecological systems. This prevalence creates the expectation of universal and detail-independent principles that can explain the emergence of patterns of synchrony. Ecological systems consisting of spatially extended noisy coupled two-cycle oscillators go through a second-order phase transition from synchrony to disorder as the stochasticity increases. In the vicinity of this critical transition, these models' dynamic and static properties show anomalies and follow detail-independent scaling relationships with critical exponents, which are usually measured at equilibrium. Working with models allows us to accommodate the long transition times to reach equilibrium. However, in reality, these transition times are often much longer than ecologically relevant timescales, which makes this approach less practical when working with real ecological data. In this study, we use the Short Time Critical Dynamics (STCD) approach to explore the universality of the time evolution of the order parameter of these models at a much shorter timescale before they reach equilibrium. |
Friday, March 18, 2022 1:18PM - 1:30PM |
Z04.00006: Jamming phase diagram for active deformable particles Francesco Arceri, Corey S O'Hern, Mark D Shattuck, Dong Wang, John D Treado, Yuxuan Cheng Numerous experiments have highlighted the important roles of cell motility and shape deformation in controlling many biological processes, such as wound-healing, cancer progression, and tissue morphogenesis. Here, we implement the active, deformable particle model (ADPM) in two dimensions, in which explicitly deformable particles are modeled as polygons with small disks at the vertices whose locations are determined by a shape-energy function that includes particle compressibility, contractility, and curvature energies. We also add cell motility to the model by having a subset of vertices move in a specific direction for a given amount of time that is determined by the cell's rotational diffusion coefficient. Using ADPM, we determine whether collections of active deformable particles are jammed or not as a function of the packing fraction, cell speed, rotational diffusion coefficient, and deformability. These studies will provide key insights into structural and mechanical properties of active, jammed tissues. |
Friday, March 18, 2022 1:30PM - 1:42PM |
Z04.00007: Configurational Fingerprints of Multicellular Living Systems Haiqian Yang, Adrian Pegoraro, Yulong Han, Wenhui Tang, Rohan Abeyaratne, Dapeng(Max) Bi, Ming Guo Cells cooperate as groups to achieve structure and function at the tissue level, during which specific structural and material characteristics emerge. Analogous to phase transitions in classical physics, transformations in these characteristics of multicellular assemblies are essential for a variety of vital processes including morphogenesis, wound healing, and cancer. In this work, we develop configurational fingerprints of particulate and multicellular assemblies, and extract volumetric and shear order parameters based on this fingerprint to quantify the system disorder. Theoretically, these two parameters form a complete and unique pair of signatures for the structural disorder of a multicellular system. The evolution of these two order parameters offers a robust and experimentally accessible way to map the phase transitions in expanding cell monolayers, and during embryogenesis and invasion of epithelial spheroids. |
Friday, March 18, 2022 1:42PM - 1:54PM |
Z04.00008: Cell junctions and spatiotemporal patterns of motion in cell monolayers Steven J Chisolm, Thomas E Angelini, Vignesh Subramaniam, Kyle Schulze, Emily Guo The suppression and emergence of collective cell motion play essential roles intissue function,occurring in healthy, diseased, and developing tissues. Cell monolayers are often used as model systems to study this collective motion. Spatiotemporal patterns of motion in epithelial monolayers have been shown to exhibit multicellular swirl-like patterns and oscillating divergent patterns at the large scale, and Fourier analysis has shown the role of short-wavelength single-cell motions like cell division. Like many in animate phases of soft matter, cell monolayers exhibit fluid-like and solid-like properties depending on observation timescales and cell packing density. Building on our previous work, in this presentation we will discuss the collective spatiotemporal patterns of motion in monolayers, focusing on how different classes of cell-cell junctions control transitions between different regimes of collective motion. Our results will connect adherens junctions to cell-cell rearrangements at long timescales, and gap junctions to intercellular fluid-flow at shorter time scales. We will discuss how these different time scales may define multiple regimes of monolayer mechanical response to applied pressure and shear stress. |
Friday, March 18, 2022 1:54PM - 2:06PM |
Z04.00009: Light-Sensitive Self-Organization in Plant Cells Nico Schramma, Cintia Perugachi Israels, Maziyar Jalaal Photosynthesis in plants is one of the main players in the survival of whole ecosystems on earth. To guarantee the efficiency of this process, plants have to actively adapt to ever-changing light conditions. Besides the well-known phototropism (the growth of plants towards the light), plants can re-arrange the internal structure of cells by the active motion of chloroplasts on short timescales. These organelles are confined between the cell membrane and vacuole and can move inside the cytoplasm via actin-mediated mechanisms. Remarkably, the simple - yet elegant - interplay of light-sensing and active forces leads to various modes of collective motion. Here, we show that the chloroplasts can behave like a densely packed light-sensitive active matter sytstem, whose non-gaussian athermal fluctuations can lead to various self-organization scenarios. In this study, we aim to establish a new framework to investigate the dynamics of active biological systems featuring intriguing dynamical phase transitions. |
Friday, March 18, 2022 2:06PM - 2:18PM |
Z04.00010: Oscillation in cell cycle times in Drosophila abdomen modeled as cell phase synchronization Riya Nandi, Andrea Cairoli, John J Williamson, Ana Ferriera, Anna Ainslie, John Davis, Nicolas Tapon, Guillaume Salbreux Analysis of tissue growth in the Drosophila abdomen has revealed that the cell cycle times are correlated in space and time. One manifestation of such correlations is through the average rate of cell division in the Histoblast nests which has been observed to oscillate with a period of roughly four hours, before decaying after 28 hAPF. As a simple explanation for such oscillations, we propose that neighbouring cells have synchronous cycles. We develop a model of the cell cycle where each cell is a phase oscillator evolving from a phase of 0 to 2π between birth and division. We then study phase synchronization for a growing and dividing population of cells on a two-dimensional lattice using a variant of the standard Kuramoto model with nearest neighbour coupling and a Gaussian noise term. Our results show that, unlike the two-dimensional Kuramoto model, this model exhibits a continuous phase transition with a true synchronous phase for high values of the coupling constant. Further, the temporal evolution of the correlation of cell phases indeed shows decaying oscillatory behaviour. |
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