Rice University

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Thesis Defense

Graduate and Postdoctoral Studies
Physics & Astronomy

Speaker: Dong Wang
Doctoral Candidate

Effect of Modularity on Evolution in Heterogeneous Environments

Tuesday, May 9, 2017
2:00 PM  to 4:00 PM

707  BioScience Research Collaborative


Biological systems are modular. One key question on the presence of modularity is: Why are biological systems modular? We show that under certain circumstances, being modular is beneficial. When the environment changes, modularity coupled with horizontal gene transfer accelerates the adaptation of individuals. We have proved this theoretically using a spin glass model of fitness, and we quantify the evolutionary advantage analytically. To make our conclusion more general, we also apply other models, such as Potts model or generalized NK model, to this problem, and we get similar results. Simulations generate results consistent with our analytical calculations. Biological populations migrate at all scales. When a population of individuals migrate, they experience heterogeneous environments. What role does modularity play in the migration process? Under what conditions is modularity helpful? We generalize the model in one environment to several correlated, heterogeneous environments with migrating individuals. We study this in two real world scenarios. First we study the migration of ancient humans in the Americas, and quantify how migration velocity depends on environmental gradient. In addition, we show that a modular knowledge system and frequent knowledge transfer accelerate the migration velocity. Second, bacteria experience heterogeneous environments, and their resistance to antibiotics emerges very fast in an antibiotic gradient. We show that a modular organization of genes accelerates this emergence of resistance, and we quantify how mutation rate, horizontal gene transfer rate, nutrients and antibiotic gradient influence this emergence. Our model may be applied to other problems such as cancer metastasis.

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