Microbial experimental evolution

Abstract

Microbes have been widely used in experimental evolutionary studies because they possess a variety of valuable traits that facilitate large-scale experimentation. Many replicated populations can be cultured in the laboratory simultaneously along with appropriate controls. Short generation times and large population sizes make microbes ideal experimental subjects, ensuring that many spontaneous mutations occur every generation and that adaptive variants can spread rapidly through a population. Another highly useful experimental feature is the ability to preserve and store ancestral and evolutionarily derived clones. These can be revived in parallel to allow the direct measurement of the competitive fitness of a descendant compared with its ancestor. The extent of adaptation can thereby be measured quantitatively and compared statistically by direct competition among derived groups and with the ancestor. Thus, fitness and adaptation need not be matters of qualitative speculation, but are quantitatively measurable variables in these systems. Replication allows the quantification of heterogeneity in responses to imposed selection and thereby statistical distinction between changes that are systematic responses to the selective regimen and those that are specific to individual populations.

Experimental evolution in fluctuating environments: tolerance measurements at constant temperatures incorrectly predict the ability to tolerate fluctuating temperatures

“…However, it is not completely understood whether selection in fluctuation actually targets the individuals that cope well with all the constant temperatures of the selection range, or does fluctuation favour individuals that have other means of adapting to the fluctuating temperature. These other kinds of adaptations to fluctuation could be for example increased reversible phenotypic plasticity (Hughes et al 2007, Bennett andHughes 2009), for example in expressing heat shock proteins (Sorensen et al 2003, Ketola et al 2004 or reversible plasticity in maximizing reproduction during short periods of optimum conditions (Gilchrist 1995, New et al 2014. Tolerance curves are very widely used in evaluating species performance, for example in breeding genetics (Falconer and Mackay 1996), in assessing the impacts of climate change on species (Deutsch et al 2008, Huey et al 2012, or in predicting the potential emergence of invasive species (Lee and Gelembiuk 2008).…”

Adaptation and Heterogeneity of Escherichia coli MC1000 Growing in Complex Environments

“…Thus, the growth of a bacterial strain in a defined medium can be maintained for hundreds or thousands of generations. Adaptation can be assessed, since the fitness of evolved forms can be compared, at any time, to that of the ancestral strain (9). Experimental evolution has thus enabled the study of the adaptation of bacteria to the conditions posed by structured versus unstructured habitats (10,11,12,13).…”

Experimental Microbial Evolution of Extremophiles

“…Adaptive laboratory evolution (ALE) selects for fitness under experimentally imposed conditions (Bennett and Hughes 2009;Dragosits and Mattanovich 2013). However, experimental evolution studies focusing on the contributions of genetic drift and natural mutation rates to evolution are conducted under non-selective conditions to avoid changes imposed by selection (Hindré et al 2012).…”