A new study published in the open-access journal PLoS ONE finds that populations of the worm Caenhorabditis elegans need 20 generations to become resistant to pesticides – that is just 80 days. The study, conducted by researchers at the Instituto Gulbenkian de Ciencia (IGC) and the Faculty of Science of the University of Lisbon, Portugal, furthers understanding of how pests and parasites respond to pesticides and antibiotics.
Levamisole is a widely used pesticide that is lethal to the nervous system of the worm C. elegans if exposed to high enough doses. In lower doses, the pesticide merely affects fecundity and mobility of the worm. Following 20 generations of the Levamisole-exposed worm, Patrícia Lopes and colleagues discovered that the pesticide significantly reduced fecundity, survival, and the frequency of males. Although males started out as about 30% of the population, they numbered 0% by the 10th generation. The researchers note that males were not necessarily more susceptible to Levamisole than females. However, the worms were less mobile after exposure to the pesticide and were unable to find mates.
This lack of males did not, though, lead to the demise of the entire worm population. As the worms adapted to this new Levamisole environment, they began to show a revival in survival and fecundity from the 10th to the 20th generation, and the number of males increased again. How was it possible to reproduce without any males? C. elegans is a hermaphrodite species, and so some worms in the population are both male and female and could breed on their own (a process called “selfing”).
The researchers then put the adapted worms into an environment with out pesticides, and the worms were able to survive without any problems. This means that there were no adaptation costs to the population. “These findings have implications for managing the application of pesticides: if we had found that the survival of adapted worms in the original environment was impaired too, this would have meant that, by maintaining areas where the pesticide is not spread, resistance to the pesticide could be controlled, and the efficacy of the pesticide increased,” said Elio Sucena (group leader at IGC and co-author of this study).
Group leader at the University of Lisbon Sara Magalhães concludes that, “As a result of the widespread use of pesticides and antibiotics, resistance to these chemicals has developed in many species. Our ability to manage this resistance entails being able to dissect the genetic changes underlying the acquisition of resistance. Our approach, using experimental evolution, allows us to manipulate several factors, such as population size, environmental stability and genetic background in our efforts to tackle and understand pesticide resistance, not only of C. elegans but also other pests and parasites.”
Rapid Experimental Evolution of Pesticide Resistance in C. elegans Entails No Costs and Affects the Mating System
Lopes PC, Sucena É, Santos ME, Magalhães S
PLoS ONE (2008). 3(11): e3741.
doi:10.1371/journal.pone.000374
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Written by: Peter M Crosta