Report

Teaser, summary, work performed and final results

Periodic Reporting for period 2 - FluctEvol (Fluctuating selection, evolution, and plasticity in random environments)

Teaser

Temporal environmental variation in natural systems includes a large component of random fluctuations, the magnitude and predictability of which is modified under current climate change. The need for predicting eco-evolutionary impacts of plastic and evolutionary responses to...

Summary

Temporal environmental variation in natural systems includes a large component of random fluctuations, the magnitude and predictability of which is modified under current climate change. The need for predicting eco-evolutionary impacts of plastic and evolutionary responses to changing environments is still hampered by lack of strong experimental evidence. FluctEvol aims at shedding a new light on population responses to stochastic environments, and facilitating their prediction, using a unique combination of approaches. First, theoretical models of evolution and demography under a randomly changing optimum phenotype will be designed and analysed, producing new quantitative predictions. Second, statistical methodologies will be developed, and employed in meta-analyses of long-term datasets from natural populations. And third, large-scale and automated experimental evolution in stochastic environments will be carried out with the micro-alga Dunaliella salina, an extremophile that thrives at high and variable salinities. We will manipulate the magnitude and predictability of fluctuations in salinity, and use high-throughput phenotyping and candidate-gene sequencing to analyse the evolution of plasticity for traits involved in salinity adaptation in this species: glycerol and carotene content. We will thus combine the benefits of experimental evolution in microbes (short generations, ample replication) with a priori knowledge of ecologically relevant adaptive traits, allowing for hypothesis-driven experiments. The success of this project in increasing our predictive power about eco-evolutionary dynamics is warranted by the experience of the PI, at the interface between theoretical and empirical approaches. Our experiments will have relevance beyond academia, as we will modify through evolution the plasticity of traits (accumulation of energetic cell metabolites) that are direct targets for bioindustry, thus potentially overcoming current limitations in productivity.

Work performed

The project is unfolding along its major methodological (theory, experimental evolution, statistical analysis of natural populations) as well as thematic (fluctuating selection, genetics of adaptation, phenotypic plasticity) axes.
The first theoretical work has investigated the population dynamic consequences of a randomly fluctuating optimum phenotype, in an evolving population. We have notably shown that the distribution of population sizes is skewed in this context, with an excess of low values where populations are at high risk of extinction. Some of the results from this analysis are the focus of the first large experiment we have conducted with the micro-alga Dunaliella salina, where ~ 1000 populations have been exposed to random fluctuations in salinity, and population size was tracked through flow cytometry and spectrophotometry.
Another aspect of the work has concerned the evolution of phenotypic plasticity. We have investigated theoretically the evolution of plasticity in extreme environments, which are rare under current patterns of environmental fluctuations, but may become common in the close future under climate change. On the experimental side, we have measured the salinity tolerance (with acclimation) of our evolved strains at the end of the long term experiment with fluctuating salinity.
Regarding analysis of natural populations, we have obtained datasets for researchers working on a range of organisms, in order to analyze fluctuating selection on phenological traits (timing of reproduction events). We have sampled natural populations of Dunaliella salina in ponds with highly different mean and temporal variance of salinity, sequenced their genomes, and measured their salinity tolerance curves, so as to investigate the genetic and physiological underpinnings of their diversity in the wild.

Final results

In the context of contemporary evolution in response to anthropogenic change, there is growing interest in the interplay between plastic and genetic responses to the environment and their impact on demography, but we still lack strong experimental evidence on these topics. Experimental evolution with microbes is a particularly useful approach to address key questions raised by theory that are difficult to investigate in the wild with higher eukaryotes. Our approach is original in that it combines experimental evolution, analysis of data from natural populations, and new theoretical predictions, about population responses to stochastic, randomly changing environments. We also aim at reaching an integrative view of the biological processes we investigate, from the genetic (and epigenetic) sequence to gene expression, phenotypes, fitness, and population growth. This combination of approaches and biological levels will yield a coherent and generalizing view of plasticity, evolution, and demography in changing environments, and make a large step in our understanding of these processes.