Statistical mechanics of genes in expanding microbial colonies

Statistical mechanics of genes in expanding microbial colonies
Kirill Korolev, Pappalardo Fellow, MIT
Date and time: Thu, May 03, 2012 - 11:15am
Location: LGRT 1033
Category: Condensed Matter Seminar
Spatial correlations and number fluctuations play an important role in evolution. Their effects become especially pronounced when organisms spread to new territories because the number of organisms at the front of the expansion is typically small. The interplay of number fluctuations and migration causes spatial genetic demixing, i.e., spatial separation of different genotypes. We formulated a simple phenomenological model that describes this genetic demixing and found a good agreement between the theory and experiments in bacterial colony biofilms. More importantly, genetic demixing affects many evolutionary processes. In particular, we showed that mutualism between two species can evolve only when it is sufficiently strong and fair, i.e., both species benefit about equally from the interactions. When the fitness advantage of mutualism is reduced, mutualism is generically lost via a directed percolation (DP) process, with the phase diagram strongly influenced by an exceptional DP2 transition.