Evolution under extraterrestrial conditions

Adaptation through natural selection of terrestrial life to extra-terrestrial conditions: lessons for Life in the Universe.

Bas Ibelings, Mridul Thomas, Daniel McGinnis (Earth Sciences and Environment Section, Departement F.-A. Forel, UniGE), Emeline Bolmont (Department of Astronomy, UniGE)

Life is defined by the capacity of Darwinian evolution. Experimental evolution has proven to be one of the most powerful tools to study the mechanisms of evolution on Earth. Evolution that drove the diversification of life from a simple and homogenous beginning. We aim to perform experimental evolution and observe which geno- and phenotypic traits will be favored under conditions found on different planets. For this we assume that there is a core to life that is similar on Earth and elsewhere, so that presently the best model system to study Life in the Universe are life-forms found on Earth. There are many organisms (facultatively) adapted to life in the absence of oxygen (e.g. methanogens, yeast). Some of these function with very simple substrates, for example methane production occurring from hydrogenotrophic processes, where the substrates could be from expelled biogases of other organisms or by carbonate rock erosion (4H2 + CO2 -> CH4 + 2H2O). These processes also alter the balance of the stable C isotopes in the system (δ13C). From this perspective, we propose conducting experiments on organism evolution in alternative environments (various substrates and initial atmospheres, such as H2 + N2 mixture or CO2). Besides quantifying the organism’s evolutionary trajectory, we propose to monitor - using existing equipment in Department Forel - the various gases consumed or produced by these organisms, i.e. to investigate what types of atmospheric gas compositions could suggest the presence of life on extra-terrestrial worlds. Studies have shown growth of unicellular prokaryotes and eukaryotes under conditions found on other planets, like the H2 dominated atmosphere of rocky exoplanets, so the potential for experimental evolution is present.

Questions of main interest:

• What are the key traits that evolve when life adapts to non-earth like conditions and what is the nature of the underlying mutations?
• What are the biosignatures found as a consequence of the evolution of new traits? Are they unique signatures of life?

In more detail:

• Does adaptation to alien substrates trigger evolution along familiar or new trade-off axes?
• How do different planetary compositions/substrates alter the evolutionary pathways and potential for adaptation of earth’s microbes?
• Do microbial communities increase their evolutionary performance on alien substrates faster than individual species (through mechanisms like cross-feeding)?
• Does adaptation of individual species vs. complex communities lead to different biosignature patterns?
• Where on Earth do the species/communities that adapt to alien substrates most rapidly originate? Are extremophiles a useful focus of research, or are other organisms and ecosystems better targets in the study of Life in the Universe?
• What is the role of natural selection vs. chance and history – which key innovations occur repeatedly?
• What are the key events in modification of the abiotic environment by evolutionary innovations, and how does this modified environment feedback on evolution of Life in the Universe?
• What is the role of varying light conditions on evolution, e.g. light coming from a Sun- like star or a Red star, with and without strong UVs?