The mutability of demographic noise in microbial range expansions

Abstract

Demographic noise, the change in the composition of a population due to random birth and death events, is an important driving force in evolution because it reduces the efficacy of natural selection. Demographic noise is typically thought to be set by the population size and the environment, but recent experiments with microbial range expansions have revealed substantial strain-level differences in demographic noise under the same growth conditions. Many genetic and phenotypic differences exist between strains; to what extent do single mutations change the strength of demographic noise? To investigate this question, we developed a high-throughput method for measuring demographic noise in colonies without the need for genetic manipulation. By applying this method to 191 randomly-selected single gene deletion strains from the E. coli Keio collection, we find that a typical single gene deletion mutation decreases demographic noise by 8% (maximal decrease: 81%). We find that the strength of demographic noise is an emergent trait at the population level that can be predicted by colony-level traits but not cell-level traits. The observed differences in demographic noise from single gene deletions can increase the establishment probability of beneficial mutations by almost an order of magnitude higher than the wild type. Our results show that single mutations can substantially alter adaptation through their effects on demographic noise and suggest that demographic noise can be an evolvable phenotype of a population.

Metabolic interactions control the spread of plasmid-encoded functional novelty during microbial range expansion

“…In some ways, understanding the fate of transconjugants has parallels with understanding the fate of random genetic mutations. The fate of random genetic mutations is fairly well-understood (Hallatschek, Hersen et al 2007, Hallatschek and Nelson 2010, Gralka, Stiewe et al 2016, Bosshard, Dupanloup et al 2017, Goldschmidt, Regoes et al 2017, Bosshard, Peischl et al 2019, Gralka and Hallatschek 2019, Yu, Gralka et al 2021). For example, both transconjugants and random genetic mutations are susceptible to selection and strong drift at the expansion frontier.…”

Exploring the expanse between theoretical questions and experimental approaches in the modern study of evolvability

“…Epigenetically inherited heterogeneity can actually increase fitness in a single environment (Cerelus et al 2016 ). It is also likely to shape demographic stochasticity and, therefore, strongly affects the survival probability of new beneficial mutations (Yu et al, 2020 ).…”

Mutant scaling laws reveal that accelerated evolution via gene amplification requires spatially structured population growth

“…An extensive theoretical understanding exists about the laws of mutant growth in exponentially expanding populations [1] [2-5] [ [6][7][8] , but an equivalent understanding for spatially structured expanding populations remains to be fully worked out. Principles of mutant evolution in spatially structured populations have been elucidated by both computational and experimental approaches [9] [10] [11] [12] [13] [ [14][15][16][17][18][19][20][21][22][23][24]. Yet, challenges exist on the computational side when large populations are considered, as is necessary in various settings, such as bacterial growth or cancer cell growth.…”