Worm Species Adapts To Pesticides In 80 Days

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, PatrГ­cia 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 MagalhГЈes 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 Г‰, Santos ME, MagalhГЈes S

PLoS ONE (2008). 3(11): e3741.

doi:10.1371/journal.pone.000374

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Written by: Peter M Crosta