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Résumé |
Regular environmental conditions allow for the evolution of
specifically adapted responses, whereas complex environments usually
lead to conflicting requirements upon the organism's response. A
relevant instance of these issues is bacterial chemotaxis, where the
evolutionary and functional reasons for the experimentally observed
response to chemoattractants remain a riddle. Sensing and motility
requirements are in fact optimized by different responses, which
strongly depend on the chemoattractant environmental profiles. It is
not clear then how those conflicting requirements quantitatively
combine and compromise in shaping the chemotaxis response. Here we
show that the experimental bacterial response corresponds to the
maximin strategy that ensures the highest minimum uptake of
chemoattractants for any profile of concentration. We show that the
maximin response is the unique one that always outcompetes motile but
nonchemotactic bacteria. The maximin strategy is adapted to the
variable environments experienced by bacteria, and we explicitly show
its emergence in simulations of bacterial populations in a chemostat.
Finally, we recast the contrast of evolution in regular vs. complex
environments in terms of minimax vs. maximin game-theoretical
strategies. Our results are generally relevant to biological
optimization principles and provide a systematic possibility to get
around the need to know precisely the statistics of environmental
fluctuations. |
