Cryptic speciation and blurred species boundaries of the earthworm: A challenge for soil-based toxicological risk assessments

Abstract

The toxicological risk assessment of chemicals is largely based on the Organization for Economic Co-operation and Development (OECD) guidelines. These internationally approved methodologies help shape policy and political strategy of environment and human health issues. Risk assessments which pertain to soil biota 'recruit' sentinel organisms, including the earthworm Eisenia fetida. Despite E. fetida being morphologically similar to Dendrobaena veneta, they are characterized by a several-fold difference in sensitivity to xenobiotics. Worms, sold as either as pure E. fetida stocks or E. fetida/D. veneta mixed cultures, were obtained from five commercial suppliers. The species identity of 25 earthworms was determined by sequencing the cytochrome c oxidase subunit 2 (COII). We revealed that only one of 25 worms was E. fetida, the remaining worms were all identified as D. veneta. This underlines the notion that E. fetida and D. veneta are easily mis-identified. The occurrence of cryptic speciation combined with the well-documented species-specific variation in toxicological responses highlights the pressing need to accurately classify earthworms to species level prior to any toxicological research. Only this will ensure the validity and reliability of risk assessments.