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This article was co-authored by Léa Frachon (co-funding Labex TULIP - Midi-Pyrénées Region) and Cyril Libourel (Paul Sabatier University thesis funding).

At what pace does a population evolve - and how does it evolve - in a heterogeneous environment?

The project, originally initiated by Fabrice Roux during his thesis in 2001, started with the sampling of seeds of a wild Arabidopsis thaliana (arabettes) in the Morvan (Bourgogne region) prairies, in which temperature increased of more than 1 ° C over the last 30 years. Harvesting the seeds of 80 plants in 2002 and 115 plants in 2010, the team had them emerged from their dormancy to plant them in September 2012. This population of arabette evolving in an environment with very variable characteristics, and more precisely under a fence separating two permanent grasslands with three different soil types and contrasting plant communities, the seeds were sown in six representative micro-habitats. For 9 months, the plants were subsequently measured for 29 traits representing the key stages of their life cycle.

A very fast adaptation

The authors observe a very rapid phenotypic adaptation regardless of the considered micro-habitat. For example, 2010 plants flourish on average 6 days later than the 2002 plants. These results suggest a population shift towards a new phenotypic optimum in less than 8 generations.

Different genetic strategies

Although the authors of the article observed a phenotypic evolution of the population that was similar between the micro-habitats tested, the genetic lines closest to the new phenotypic optimum were not the same, suggesting different adaptive genetic bases according to the micro-habitat considered. By sequencing the genome of the 195 genetic lines and carrying out genetic association studies, the authors confirmed this hypothesis.
Thus, in response to climate change, this local population of arabettes has evolved towards a new phenotypic optimum by adopting different genetic strategies according to micro-habitats. Such a mechanism would therefore allow the maintenance of genetic diversity in the presence of natural selection.

"Populations in general could therefore evolve and adapt without genetic diversity loss. This suggests that it will be necessary not only to preserve the diversity of species but also genetic diversity within the same species if we want them to be able to respond to the global changes to come. Natural selection would have favored this genetic architecture allowing to adapt to selection pressures which can be very fluctuating during the generations." concludes Fabrice Roux.