The effects of metals and food availability on the behavior of Caenorhabditis elegans.

Caenorhabditis elegans, a nonparasitic soil nematode, was used to assess the combined effects of metal exposures and food availability on behavior. Movement was monitored using a computer tracking system after exposures to Cu, Pb, or Cd while feeding was measured as a change in optical density (deltaOD) of bacteria suspensions over the exposure period. After 24-h exposures at high and low bacteria concentrations, movement was decreased in a concentration-dependent fashion by Pb and Cd but feeding reductions were not directly proportional to exposure concentrations. Copper exposure induced concentration-dependent declines in feeding and movement regardless of bacteria concentration. The impact of 24-h metal exposures was apparently reduced by increasing food availability. Therefore, exposures were shortened to 4 h in an attempt to minimize starvation effects on movement. Although nematodes were immobilized following 24 h of food depravation, worms deprived of food during the 4-h exposure continued to feed and move after exposure. A bead-ingestion assay after 4-h exposures was also used as an additional means of assessing the effects of metals on feeding behavior. Ingestion was significantly reduced by all concentrations of metals tested, indicating its sensitivity as a sublethal assay. Feeding (deltaOD) during exposures exhibited similar trends as ingestion but was slightly less sensitive, while movement was the least sensitive assay of 4-h metal exposures to C. elegans. Assessment of multiple sublethal endpoints allowed for the determination of the separate and interactive effects of metals and food availability on C. elegans behavior.