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Experimental evolutionary rescue of Paramecium caudatum under rapid environmental change

Sascha Krenek
Berendonk - Technical University of Dresden, Germany
Kaltz - University of Montpellier, France
Monday, March 9, 2015 to Sunday, March 22, 2015

Environmental change is probably the most common cause of biological extinctions ever since life has existed. At the same time, extinction can be prevented through adaptation, and this is why environmental change provides a most powerful and perpetual engine of biological diversification. That organisms adapt to the environment is a truism. But it is far less trivial that evolution may play an important role in finite populations over short time scales, typically considered "ecological". This idea is at the heart of the concept of Evolutionary Rescue (ER), which provides the framework to study the capacity of populations to survive rapid environmental change. It links demography and evolution in finite populations, by describing the outcome of a race between population decline and the rise of beneficial mutations. Understanding rapid adaptation processes is essential for global climate change research and conservation issues, but also concerns aspects of antibiotic resistance, sustainable biological pest control and pathogen management. The topic has also caught immediate attention from experimentalists, and it turned out that the very essential feature of ER (U-shaped pattern of population density) can be captured through experimental evolution in highly replicated microcosm populations of microbes or small organisms.

Our project aims at investigating ER through such an experimental evolution approach, using the microbial model freshwater ciliate Paramecium. Namely, we will address the interplay between ecological conditions (rate of environmental change), the probability of ER and the evolutionary trajectories leading to ER. We are particularly interested in the underlying (epi)-genetic mechanisms and in the potential consequences for genetic structure of adapted populations, once ER has occurred. Our project has a strong focus on molecular analyses, aiming at elucidating the link between adaptation and (epi)-genetic change.

Based on an ongoing long-term experiment, investigating ER under different rates of temperature increase, we have set up a follow-up long-term experiment during the STSM investigating the effect of ER history on genetic correlations of stress resistance to further stresses. Currently, it is not a priori clear whether adaptation will constrain or facilitate future evolution. In this initial experiment we will test for pre-adaptation of high-temperature adapted lines to even higher and normally lethal temperatures. In future experiments we aim to screen the responses of selected pre-adapted lines to a variety of other stressors, both abiotic (osmotic, pH, herbicide, etc) and biotic (parasites, predators, competitors). This will allow us to test for general patterns of pre-adaptation and constraint, as a function of the evolutionary history of the populations. Additional to the evolutionary experiments we will investigate molecular evolution processes via gene expression profiling using the RNA-Seq approach. The expected transcription profiles will allow us to detect differentially altered expression patterns at a genome-wide scale. These ‘pooled population transcriptome’ data will further point us to newly transcribed genes that might produce the observed fitness differences between our selection lines.

During the STSM, Oliver Kaltz and I have also discussed and drafted a joint research proposal to study the dynamics and its underlying genetic and epigenetic basis of rapid adaptation during Evolutionary Rescue.


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