Comparison of lethality, reproduction, and behavior as toxicological endpoints in the nematode Caenorhabditis elegans

This study describes a new approach for assessing behavioral changes following toxicant exposure and compares the method to other common endpoints used in environmental toxicology. The nematode Caenorhabditis elegans was exposed to a range of ethanol concentrations to determine its effect on survival, reproduction and behavior. Each endpoint was evaluated for its sensitivity by comparing LC50, RC50 (concentration at which there is a 50% reduction in number of offspring as compared to controls), and BC50 (concentration at which there is a 50% reduction in movement as compared to controls) values for ethanol exposure. Worms showed 24-h lethality at concentrations of ethanol in the range of 83 g/L to 99 g/L. Reproduction in C. elegans was estimated by counting the number of off-spring after 3 d of exposure, which decreased with the increase in ethanol concentration from 8 g/L to 71 g/L. Behavior was quantified by using a new computer tracking method, which can simultaneously assess hundreds of nematodes and provides several behavioral parameters in real time. Worms showed some hyperactivity (increased movement) at very low ethanol concentrations (0.8 g/L and 2.4 g/L) and a decrease in movement at higher ethanol concentrations (4 g/L to 40 g/L). A comparison for sensitivity between the three endpoints was performed. Behavior and reproduction responses were found to be similar and, as expected, both are much more sensitive indicators of toxicity than lethality. The advantages and disadvantages of the computer tracking system are discussed.