Ecotoxicology, ecophysiology, and mechanistic studies with rotifers

Invertebrates play an increasing role in assessing the impacts of environmental contaminants in aquatic ecosystems. Substantial efforts were made to identify suitable and environmentally relevant models for toxicity testing. Rotifers have a number of promising characteristics which make them candidates worth considering in such efforts. They are small, simple in their organization, genetically homozygous, easy to cultivate. Rotifers are further widely distributed and ecologically important in freshwaters, in estuaries and coast, and also play an important role in the transportation of aquatic pollutants across the food web. In the last decades there has been a substantial increase of contributions on rotifers, particularly in areas of their ecology, geophylogeny, genomics and their behavioral, physiological, biochemical and molecular responses, following exposure to environmental chemicals and other stressors. Gene expression analysis enables ecotoxicologists to study molecular mechanisms of toxicity. Rotifers also appear as useful tools in the risk assessment of pharmaceuticals and their metabolites that find their way into aquatic ecosystems because their sensitivity to some of these substances is higher than that of cladocerans and algae. In respect to endocrine disruptors, rotifers seem to be particularly sensitive to androgenic and anti-androgenic substances, whereas copepods and cladocerans are typically more affected by estrogens and juvenile hormone-like compounds. Generally, a combination of whole-animal bioassays and gene expression studies allow an understanding of toxicological mechanisms. The purpose of this review is to demarcate the potential of using rotifers as important invertebrate aquatic model organisms for ecophysiology, ecotoxicology and environmental genomics. This review does not claim to find reasons for a superior use of rotifers in these fields. But the different phylogenetic allocation of rotifers in the Platyzoa (formerly Nemathelminthes) justifies its consideration since there are evolutionary differences in biochemical and genetic performances that need to be considered. Problems, controversials and needs for further studies are discussed. We are providing a literature survey here for the last 15 years that shows a steady increase of ecotoxicological research on rotifers.