Curiosity did not kill the worm

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A group of gregarious worms feeding on fluorescent bacteria.


Caenorhabditis elegans are non-parasitic roundworms commonly found in rotten fruits munching on bacteria. Adults are approximately 1 mm long.

Most individuals are hermaphrodites and reproduce by selfing, laying up to 300 eggs per worm within 5 days of being born. Therefore, large populations of worms can be cultured easily in the laboratory in Petri dishes filled with agar, where the worms feed on vast "lawns" of bacteria (Escherichia coli) growing on the surface. Under these conditions, we can distinguish two types of worms: solitary worms that forage individually and distribute themselves evenly throughout the food area, and gregarious worms that aggregate and forage at the border of the lawn. This striking difference in behavior is explained by a single amino-acid change in the protein coded by the npr-1 gene. In humans, proteins similar to NPR-1 are thought to be involved in alcoholism, obesity and mood disorders. How are the two behaviors maintained in nature? Graduate student Andrea Gloria-Soria and Dr. Ricardo Azevedo from the Department of Biology and Biochemistry at the University of Houston have shown that gregarious and solitary worms consume different parts of a food resource, thus avoiding direct competition. In addition, they found that the two genotypes differ in their ability to spread to new food sources: gregarious worms tend to move between food patches at a faster rate than solitary worms. This difference in "curiosity" provides further opportunities to "split" food resources. When the two types of worms were allowed to compete against each other in different environments, solitary worms performed much better than gregarious ones when grown in a single, large bacterial lawn. In contrast, the gregarious worms improved when the food was presented to them as several small lawns, presumably because of their increased ability to disperse.

The natural habitat of C. elegans is thought to be composed of ephemeral patches of bacteria. The study of Gloria-Soria and Azevedo suggests that the balance between the ability to compete for an already occupied resource and the ability to colonize new resources might maintain the
npr-1 polymorphism in nature.

Gloria-Soria A & Azevedo RBR (2008) npr-1 regulates foraging and dispersal strategies in Caenorhabditis elegans. Current Biology 18: