Environmental heterogeneity can tip the population genetics of range expansions
Abstract
The population genetics of most range expansions is thought to be shaped by the competition between Darwinian selection and random genetic drift at the range margins. Here, we show that the evolutionary dynamics during range expansions is highly sensitive to additional fluctuations induced by environmental heterogeneities. Tracking mutant clones with a tunable fitness effect in bacterial colonies grown on randomly patterned surfaces we found that environmental heterogeneity can dramatically reduce the efficacy of selection. Time-lapse microscopy and computer simulations suggest that this effect arises generically from a local 'pinning' of the expansion front, whereby stretches of the front are slowed down on a length scale that depends on the structure of the environmental heterogeneity. This pinning focuses the range expansion into a small number of 'lucky' individuals with access to expansion paths, altering the neutral evolutionary dynamics and increasing the importance of chance relative to selection.
Data availability
All data generated or analysed during this study are included in the manuscript and supporting files. Source data files have been provided for all figures.
Article and author information
Author details
Funding
Simons Foundation
- Oskar Hallatschek
National Science Foundation
- Oskar Hallatschek
National Institute of General Medical Sciences
- Oskar Hallatschek
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Reviewing Editor
- Richard A Neher, University of Basel, Switzerland
Version history
- Received: December 18, 2018
- Accepted: April 11, 2019
- Accepted Manuscript published: April 12, 2019 (version 1)
- Version of Record published: May 13, 2019 (version 2)
Copyright
© 2019, Gralka & Hallatschek
This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.
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