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Sex and the maintenance of diversity in heterogeneous habitats

Final Activity Report Summary - EVOL HET ENV (Sex and the maintenance of diversity in heterogeneous habitats)

The evolution of drug resistance is a key issue of both fundamental and applied importance. Most organisms have evolved resistance for nearly all pesticides used. Despite major breakthroughs achieved with studies on natural populations, some avenues of research remain unexplored due to a lack of a suitable system amenable to experimental manipulation at the ecological and evolutionary timescale. With this project, we aimed at contributing to the current knowledge on this topic by tackling the process of pesticide resistance using the model organism Caenorhabditis elegans and levamisole, a widely used nematicide for which the mechanism of action and the genetic basis of resistance are known.

By creating lines of experimental evolution subjected to levamisole or to a control environment, we aimed at testing whether an outcrossed population of C. elegans adapted to levamisole within a short timescale. In addition, we measured whether adaptation entailed a cost in performance in the ancestral environment.

Finally, we assessed the consequences of such adaptation to the susceptibility to another widely used pesticide, Ivermectin. Since the two nematicides operate on either the inhibitory or the excitatory neural networks, a strong trade-off in adaptation to the two pesticides is expected. That is, nematodes may develop resistance to one of the pesticides, but this is expected to entail an increase in susceptibility to the other pesticide.

We found that populations exposed to Levamisole developed resistance at a very fast rate. Indeed, survival of C. elegans exposed to levamisole was near to 100 % within 20 generations and their fecundity increased relative to control populations. In addition, this resistance did not entail a cost in the ancestral environment or in Ivermectin. These results suggest that pesticide resistance is indeed a threat to natural populations