Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session L68: The Many Dimensions of EvolutionInvited Undergrad Friendly
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Sponsoring Units: DBIO Chair: Mikhail Tikhonov, Washington University, St. Louis Room: Four Seasons 4 |
Wednesday, March 4, 2020 8:00AM - 8:36AM |
L68.00001: The ecology and evolution of collective behavior Invited Speaker: Deborah Gordon Ant colonies operate without central control, using feedback from simple olfactory interactions to regulate their activities. There are more than 14K species of ants in every habitat on Earth, using diverse stochastic algorithms, producing different feedback regimes, in different environments. These algorithms have evolved to fit the dynamics of particular environments, including energy flow, stability, and the threat of rupture. Harvester ants in the harsh but stable conditions of the desert, regulate foraging effort according to current food availability and humidity, using excitable dynamics based on the rate of contact inside the nest between returning and outgong foragers. The feedback system sets a default of inactivity unless conditions are favorable. For turtle ants in the trees of the tropical forest, high humidity makes activity easy but competition is high. Their trail networks are constrained to follow the nework of vegetation. They use the rate of deposition of a volatile pheromone to build and maintain a distributed routing network in heterogeneous environments, based on design principles that differ from the shortest paths commonly studied in ants and in network science. The feedback system sets a default of persistent activity unless conditions are unfavorable. The diversity of ants provides opportunities to learn how collective behavior evolves to fit diverse environmental dynamics. |
Wednesday, March 4, 2020 8:36AM - 9:12AM |
L68.00002: Attack of the clones: what causes population structure in bacteria and how can we use it? Invited Speaker: William Hanage In most pathogenic bacteria, the population is made up of multiple distinct lineages or ‘clones’ which are associated with properties like virulence or drug resistance. For the most part, this structure has been taken for granted and its root causes not been examined. We have recently shown, using the pneumococcus as a model organism, that we can explain which clones are present in a community with a simple model of negative frequency dependent selection operating on a subset of the genome: namely the accessory genome of loci not present in all isolates of the species. Moreover, we can use this to predict the consequences of removing some clones, for instance through vaccination. This can be achieved either through a game theory approach using the replicator equation, or through quadratic programming to determine how the equilibrium properties of the population as a whole can be restored by altering the proportions of each clone. Finally the existence of clones offers an opportunity to use emerging DNA sequencing technologies to rapidly detect them in clinical samples, which could be useful for detecting and responding to drug resistant threats. |
Wednesday, March 4, 2020 9:12AM - 9:48AM |
L68.00003: Evolutionary dynamics in large microbial communities Invited Speaker: Benjamin Good Microbial communities drive important biochemical cycles, from the ocean to the soil to the human gut. High rates of cell turnover endow these communities with an enormous potential for rapid evolutionary change – e.g., billions of new mutations are produced within a single gut microbiome every day. Despite the potential importance of these effects, we currently know very little about the evolutionary dynamics that take place in large microbial communities, and how these dynamics might deviate from our single-species intuition. In this talk, I will describe our recent efforts to address this question using data from the human gut microbiome. I will show how population genetic analysis of sequenced fecal samples can help us quantify the typical timescales of within-host evolution, and how this might constrain the ability of a community to adapt to fluctuating environmental conditions. |
Wednesday, March 4, 2020 9:48AM - 10:24AM |
L68.00004: Microbial interactions across time and space Invited Speaker: Britt Koskella There is great interest in explaining microbial diverstiy, but a critical first step that is often downplayed is understanding the spatial and temporal scales that are relevant to the system. In this talk I discuss the relative importance of interactions among bacteria and phage viruses, between bacterial strains and species within a microbiome, and between a host and its symbionts to emphasize the role of evolution and coevolution in shaping diversity across scales. I focus primarly on the plant phyllosphere as a model system to explore these interactions both in natural, ecologically complex, and simple experimental systems. |
Wednesday, March 4, 2020 10:24AM - 11:00AM |
L68.00005: Phenotypic heterogeneity between genetically identical cells permits growth with lethal levels of formaldehyde stress Invited Speaker: Christopher Marx Scientists tend to appreciate microbes for their simplicity and predictability: a population of genetically identical cells inhabiting a uniform environment is expected to behave in a uniform way. However, counter-examples to this assumption are frequently being discovered, forcing a re-examination of the relationship between genotype and phenotype. In most such examples, bacterial cells are found to split into two discrete populations, for instance growing and non-growing. Here, we report the discovery of a novel example of microbial phenotypic heterogeneity in which cells are distributed along a gradient of phenotypes, ranging from low to high tolerance of a toxic chemical. Furthermore, we demonstrate that the distribution of phenotypes changes in different growth conditions, and we use mathematical modeling to show that cells may change their phenotype either randomly or in a particular direction in response to the environment. Our work expands our understanding of how a bacterial cell's genome, family history, and environment all contribute to its behavior, with implications for the diverse situations in which we care to understand the growth of any single-celled populations. |
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