Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session F15: Population Ecology and Evolutionary DynamicsFocus
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Sponsoring Units: GSNP DBIO Chair: Marek Cieplak, Institute of Physics, Polish Academy of Science Room: 274 |
Tuesday, March 14, 2017 11:15AM - 11:51AM |
F15.00001: Ising universality describes emergent long-range synchronization of coupled ecological oscillators Invited Speaker: Andrew Noble Understanding the synchronization of oscillations across space is fundamentally important to many scientific disciplines. In ecology, long-range synchronization of oscillations in spatial populations may elevate extinction risk and signal an impending catastrophe. The prevailing assumption is that synchronization on distances longer than the dispersal scale can only be due to environmental correlation. By contrast, recent work shows how scale-invariant synchronization can emerge from locally coupled population dynamics. In particular, we have found that the transition from incoherence to long-range synchronization of coupled ecological two-cycles is described by the Ising universality class. I will discuss evidence that an Ising critical point describes long-range correlations found in data on the individual yields of female pistachio trees in a large orchard. [Preview Abstract] |
Tuesday, March 14, 2017 11:51AM - 12:03PM |
F15.00002: A collective phase in resource competition in a highly diverse ecosystem Mikhail Tikhonov, Remi Monasson Recent technological advances uncovered that most habitats, including the human body, harbor hundreds of coexisting microbial ``species''. The problem of understanding such complex communities is currently at the forefront of medical and environmental sciences. A particularly intriguing question is whether the high-diversity regime (large number of species $N$) gives rise to qualitatively novel phenomena that could not be intuited from analysis of low-dimensional models (with few species). However, few existing approaches allow studying this regime, except in simulations. Here, we use methods of statistical physics to show that the large-$N$ limit of a classic ecological model of resource competition introduced by MacArthur in 1969 can be solved analytically. Our results provide a tractable model where the implications of large dimensionality of eco-evolutionary problems can be investigated. In particular, we show that at high diversity, the MacArthur model exhibits a phase transition into a curious regime where the environment constructed by the community becomes a collective property, insensitive to the external conditions such as the total resource influx supplied to the community. [Preview Abstract] |
Tuesday, March 14, 2017 12:03PM - 12:15PM |
F15.00003: The type VI secretion system impacts bacterial invasion and population dynamics in a model intestinal microbiota Savannah L. Logan, Drew S. Shields, Brian K. Hammer, Joao B. Xavier, Raghuveer Parthasarathy Animal gastrointestinal tracts are home to a diverse community of microbes. The mechanisms by which microbial species interact and compete in this dense, physically dynamic space are poorly understood, limiting our understanding of how natural communities are assembled and how different communities could be engineered. Here, we focus on a physical mechanism for competition: the type VI secretion system (T6SS). The T6SS is a syringe-like organelle used by certain bacteria to translocate effector proteins across the cell membranes of target bacterial cells, killing them. Here, we use T6SS+ and T6SS- strains of V. cholerae, the pathogen that causes cholera in humans, and light sheet fluorescence microscopy for in vivo imaging to show that the T6SS provides an advantage to strains colonizing the larval zebrafish gut. Furthermore, we show that T6SS+ bacteria can invade and alter an existing population of a different species in the zebrafish gut, reducing its abundance and changing the form of its population dynamics. This work both demonstrates a mechanism for altering the gut microbiota with an invasive species and explores the processes controlling the stability and dynamics of the gut ecosystem. [Preview Abstract] |
Tuesday, March 14, 2017 12:15PM - 12:27PM |
F15.00004: Extreme value statistics and finite-size scaling at the ecological extinction/laminar-turbulence transition Hong-Yan Shih, Nigel Goldenfeld Experiments on transitional turbulence in pipe flow seem to show that turbulence is a transient metastable state since the measured mean lifetime of turbulence puffs does not diverge asymptotically at a critical Reynolds number. Yet measurements reveal that the lifetime scales with Reynolds number in a super-exponential way reminiscent of extreme value statistics, and simulations and experiments in Couette and channel flow exhibit directed percolation type scaling phenomena near a well-defined transition. This universality class arises from the interplay between small-scale turbulence and a large-scale collective zonal flow, which exhibit predator-prey behavior. Why is asymptotically divergent behavior not observed? Using directed percolation and a stochastic individual level model of predator-prey dynamics related to transitional turbulence, we investigate the relation between extreme value statistics and power law critical behavior, and show that the paradox is resolved by carefully defining what is measured in the experiments. We theoretically derive the super-exponential scaling law, and using finite-size scaling, show how the same data can give both super-exponential behavior and power-law critical scaling. [Preview Abstract] |
Tuesday, March 14, 2017 12:27PM - 12:39PM |
F15.00005: Even parasites have parasites: oscillatory population dynamics of mobile genetic elements in your genome Chi Xue, Nigel Goldenfeld Transposable elements (TEs), or transposons, are a class of mobile genetic elements that can either move or duplicate themselves in the genome, sometimes interfering with gene expression as a result. Some TEs can code all necessary enzymes for their transposition and are thus autonomous, while non-autonomous TEs are parasitic and must depend on the machinery of autonomous ones. I present and solve a stochastic model to describe the dynamics of non-autonomous/autonomous pairs of retrotransposons in the human genome that proliferate by a copy-and-paste mechanism. We predict noise-induced persistent oscillations in their copy numbers, analogous to predator-prey dynamics in an ecosystem. We discuss if it is experimentally feasible to measure these phenomena in the laboratory and to observe them over evolutionary time through bioinformatics. This work shows that it is fruitful to regard the genome as an ecosystem that is host to diverse interacting populations. [Preview Abstract] |
Tuesday, March 14, 2017 12:39PM - 12:51PM |
F15.00006: Modeling Transformation and Conjugation in Bacteria Populations John Russo, J.J. Dong The rise of antibiotic resistance in bacteria populations is a growing threat to medical treatment of diseases. Transformation, where a cell absorbs a plasmid from its environment, and conjugation, direct transfer of a plasmid from one cell to another, are the two main mechanisms of emergence of antibiotic resistance. We model the processes using a combined approach of Kinetic Monte Carlo simulation and differential equations to describe the plasmid-carrying and plasmid-free populations. Through analysis of our results, we characterize the conditions that lead to dominance of the antibiotic resistant population. [Preview Abstract] |
Tuesday, March 14, 2017 12:51PM - 1:03PM |
F15.00007: Downsides and benefits of unicellularity in budding yeast Gabor Balazsi, Lin Chen, Jennie Kuzdzal-Fick Yeast cells that do not separate after cell division form clumps. Clumping was shown to aid utilization of certain sugars, but its effects in stressful conditions are unknown. Generally speaking, what are the costs and benefits of unicellularity versus clumping multicellularity in normal and stressful conditions? To address this question, we evolved clumping yeast towards unicellularity by continuously propagating only those cells that remain suspended in liquid culture after settling. Whole-genome sequencing indicated that mutations in the \textit{AMN1} (antagonist of mitotic exit network) gene underlie the changes from clumping to unicellular phenotypes in these evolved yeast cells. Simple models predict that clumping should hinder growth in normal conditions while being protective in stress. Accordingly, we find experimentally that yeast clumps are more resistant to freeze/thaw, hydrogen peroxide, and ethanol stressors than their unicellular counterparts. On the other hand, unicellularity seems to be advantageous in normal conditions. Overall, these results reveal the downsides and benefits of unicellularity in different environmental conditions and uncover its genetic bases in yeast. [Preview Abstract] |
Tuesday, March 14, 2017 1:03PM - 1:15PM |
F15.00008: Effect of Environmental Deterioration on Interspecies Competition Clare Abreu, Jonathan Friedman, Billy Woltz, Jeff Gore A major challenge in ecology is to understand how the outcome of interspecies competition will change in deteriorating environments, in which increased mortality can result from events such as global warming. Simple phenomenological models such as the Lotka-Volterra competition model predict that increased mortality will favor the fast-growing species, potentially reversing the competitive outcome. To explore this theoretical prediction, we have performed laboratory competition experiments between soil bacteria, using a variable dilution rate to tune mortality. Consistent with expectations from theory, we find that increasing dilution rate can reverse the pairwise outcome from dominance of the slow grower to dominance of the fast grower, often with an intermediate coexisting or bistable phase. We find that these predictable effects extend to three-species competition, where varying dilution rates can lead to up to four different qualitative regimes of competitive outcomes. Moreover, we find that the pairwise outcomes can be used to predict survival in the trios with greater than 90\% accuracy. These results argue that simple phenomenological models can provide powerful insight into the effects of deteriorating environments on community structure. [Preview Abstract] |
Tuesday, March 14, 2017 1:15PM - 1:27PM |
F15.00009: A field-theoretic approach to the May-Leonard cyclic population dynamics model Shannon R Serrao, Uwe C T\"auber Spatially extended stochastic population dynamics models with cyclic predation interactions display intriguing time evolution and spontaneous structure formation. We study a general May-Leonard cyclic competition model in d dimensions with diffusive particle propagation. We use the second-quantized Doi-Peliti formalism and ensuing coherent-state path integral representation to construct its continuum representation and explore its collective dynamics. Expanding the resulting action about the mean-field species concentrations enables us to compute the diagonalized harmonic propagators and hence relaxation rates and oscillation frequencies. Furthermore, we identify the constraints necessary for time scale separation that allows us to project out the purely relaxing eigenmode. The remaining oscillating fields obey the complex Ginzburg-Landau equation, which is consistent with spiral pattern formation. We determine the parameter regimes for our stochastic model that lead to the emergence of spiral patterns, and for which the time-dependent complex Ginzburg-Landau equation with additive white noise provides an adequate (reduced) description. [Preview Abstract] |
Tuesday, March 14, 2017 1:27PM - 1:39PM |
F15.00010: Ising model behavior in coupled, one-dimensional ecological oscillators Saba Karimeddiny, Andrew Noble, Jonathan Machta, Alan Hastings The emergent behavior of coupled populations provides important insight into the persistence and extinction-risk of metapopulations. We study a one-dimensional system of noisy, coupled, logistic maps and demonstrate that there is a correspondence between the behavior of the linear chain of coupled noisy logistic maps -- a dynamical system -- with that of the one-dimensional Ising model -- a thermodynamic system. This correspondence becomes exact at the zero temperature critical point. [Preview Abstract] |
Tuesday, March 14, 2017 1:39PM - 1:51PM |
F15.00011: An Upper Bound to Catastrophe Size in Ecosystems Dervis Vural, Vu Nguyen Ecological systems and complex chemical reactions are well described by the law of mass action. If one or more new species is introduced into the system due to a mutation or migration event, the system state can undergo significant displacements, in some cases, including mass extinction. In the context of ecological and evolutionary engineering, species may also be designed or chosen to be injected into the system, to steer the system to a more desirable state. Here we present exact analytical formulas that constrain the magnitude of singular transitions in reaction networks, and discuss their implications on ecological engineering and natural evolution. [Preview Abstract] |
Tuesday, March 14, 2017 1:51PM - 2:03PM |
F15.00012: Evolutionary learning of adaptation to varying environments through a transgenerational feedback BingKan Xue, Stanislas Leibler Organisms can adapt to a randomly varying environment by creating phenotypic diversity in their population, a phenomenon often referred to as “evolutionary bet-hedging”. The favorable level of phenotypic diversity depends on the statistics of local environmental variations. Often, the timescale of environmental variations can be much longer than the lifespan of individual organisms. How could organisms collect such long-term environmental information to adjust their phenotypic diversity? We propose here a general mechanism of “evolutionary learning” based on a transgenerational feedback: the frequency of the parent phenotype is progressively reinforced in the distribution of phenotypes among the offspring. This mechanism can in principle be realized through known molecular processes of epigenetic inheritance, observed in some model organisms. Thus, our theory may provide a perspective for understanding the evolutionary significance of such processes. [Preview Abstract] |
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