Predicting contemporary evolution and population persistence in a changing environment – ContempEvol

We combine two types of approaches. On the one hand, theoretical models allow making predictions that can be tested on contemporary evolution data, or are inspired by mechanisms highlighted by such data. These models essentially consist of a mathematical formalization of processes, followed by their analysis aiming at revealing aspects of their behavior that are not easy to intuit. This theory concerns notably the effect of genetic correlation between traits on adaptation to changing environments, the impact of adaptation on reproductive isolation and the origination of new species, or the evolution of age-dependent plasticity. On the other hand, we perform empirical studies on the crustacean Artemia, whose relatively simple niche (salinity, temperature, few predators) can easily be reproduced in the lab. We combine laboratory experiments on adaptation to salinity (investigating notably the contribution of phenotypic plasticity, and of the microbiome), with a monitoring of natural populations in the field. The latter includes both a sampling of current populations, and an analysis of diapaused eggs extracted from old sediments. This work is primarily carried out by a PhD student funded by the grant.

We have already obtained a number of preliminary results. Firstly, a model of adaptation to a randomly fluctuating environment allowed quantifying how much genetic correlations between traits constrain the average response to selection, and the long-term growth rate of a population. Secondly, we have shown in another theoretical study how the complexity of the ecological niche influences the establishment of reproductive isolation between populations adapting to a changing environment, thus initiating the formation of new species. On the empirical side, we have set up our methodologies on several key points of the project, notably: (i) isolating ancient cysts from the sediments, and extracting their DNA; (ii) measuring body shape using morphometrical approaches, allowing a quantification of phenotypic plasticity; (iii) raising Artemia at high salinity, which requires acclimation steps at, and (iv) semi-sterile raising of artemia, and culturing of bacteria extracted from their guts, in order to study the role of the microbiome on adaptation to salinity.

The theoretical analysis of the effect of genetic correlations on responses to selection will be a starting point for a study on the evolution of genetic correlations, and how the latter may accelerate adaptation in a changing environment. We also plan to launch a large scale experiment on adaptation to salinity in Artemia. Clones of an asexual species will be placed at several temperatures at different stages of development, and their phenotypes will be measured to quantify plasticity. Their fitness will then be measured at another. This experiment will allow studying the effect of lag times in the establishment of plastic responses, and the variances and covariances of plasticity of mutliple traits. These two points are often what limits the application of models on the evolution of plasticity to natural populations. This empirical study will be paired with a theoretical analysis of the evolution of age-dependent plasticity.

Two review articles on the topic of this project are accepted in Functional Ecology and Philosophical Transactions of the Royal Society B, with the coordinator of the project as the first author, and in collaboration with foreign researchers (UK, USA). A theoretical article is currently been reviewed for the second time for Evolution. The results of this paper have also been presented at two exceptional international confences: The 4th international conference on quantitative genetics in Edinburgh, and the 1st joint congress on evolution in Ottawa. The project coordinator was also invited to seminars and workshops in France and abroad (Netherlands, UK…)

While evolutionary biology has long been mainly a retrospective science, the advent of contemporary evolution studies where changes in populations are followed in real time (either in the lab or in the wild) opens a new window for a more prospective approach. Indeed this type of studies focuses directly on the dynamical processes of population responses to changing environments, rather than simply on their static consequences. On the one hand, this enables a more direct comparison of models with data, and a better assessment of their predictive capacities. On the other hand, it leads to a reevaluation of the importance of previously neglected biological mechanisms, such as the direct response of individuals to their environment of development through phenotypic plasticity, or the interactions between evolution and demography.
This project aims at generating new theoretical predictions that can be tested using contemporary evolution data, and measuring in the laboratory biological parameters that are essential for predicting evolutionary and demographic responses to environmental change. The project has three main objectives, starting from the most fundamental mechanisms of response to changing environments, towards more realistic situations of contemporary evolution. First we will study how natural selection on the phenotype changes with the environment, and how this translates into a genetic response. We will focus in particular on genetic correlations between traits, which can slow down evolution and thereby increase extinction risk. Second we will investigate the evolution of plasticity, with a particular interest for correlated plasticity of multiple characters, and age-dependent patterns of plasticity, two phenomena that are widespread in nature but have been little studied theoretically and empirically. Thirdly, we will address specific situations of contemporary evolution, where the growth of populations depends on their evolution: biological invasions, and population persistence in the face of global change.
The theoretical side of the project will rely on mathematical and computer modelling of processes, which is the domain of expertise of the project coordinator (L-M Chevin). The experiments will be mostly carried out by a PhD student, who will use the brine shrimp Artemia as a biological model. This organism inhabits hypersaline continental environments. It has a simple ecological niche that can be easily manipulated in the laboratory by varying salinity and temperature. A post-doctoral researcher will also be hired to study experimental evolution of the bacteria Escherichia coli facing pH stress.
The combination of theoretical result and their experimental validation with different organisms will shed a new light on experimental evolution data, and will allow testing more rigorously the predictions of models of evolution in response to environmental change. Beyond a better understanding of the underlying biological processes, the objective of this project is also to quantitatively assess the ability of evolutionary biology to produce accurate predictions. This capacity is the prerequisite to any application of this fundamental scientific field to questions of practical concern, such as the management of antibiotics resistance, or the maintenance of biodiversity in the face of global change.