Water fleas and toxicity testing

The genome of the water flea Daphnia pulex has been sequenced for the first time. Its DNA contains the largest number of genes ever recorded for a multicellular animal, and could help check the toxicity of chemicals or environmental pollutants without experiments on rats or mice.

Daphnia is a small crustacean found in water all over the world and an important food source for fish. The authors of a study have identified 30,907 genes in its genome; more than one-third of them are not seen in any other organism.

This study is relevant because scientists want to investigate toxins that could be dangerous to the environment or to human health. But until now, studies have been limited to traditional model organisms whose genomes have been sequenced, such as fruit fly (Dosophila melanogaster) or mouse (Mus musculus). This is not so good because the genes considered most important by ecological geneticists are difficult to find in traditional model organisms kept under controlled laboratory conditions. Daphnia, however, is an ecologically-relevant organism that, with the genome in hand, will allow scientists to test the environment.

Daphnia has unusual biology that could be used to get a lot of crucial information. For example, Daphnia eggs can lay dormant in sediments for hundreds of years, so scientists can trace past population-level adaptations to environmental stresses, such as metal toxicities from mining. The crustacean can also clone itself, so ecologists will be able to expose individual genetically identical water fleas to different environmental stressors and track changes in their gene expression.

Extracted from an article by Virginia Gewin in Nature News. Picture by Science/AAAS.