| Many organisms develop antipredator defenses in the presence of a predator. One example includes Daphnia pulex juveniles, which develop neck teeth in the presence of predator kairomone (K(+)) produced by Chaoborus spp. Recent studies have demonstrated that exposure to Cu or Ni at environmentally relevant concentrations inhibits the ability of D. pulex to develop neck teeth. The mechanism of metal-induced inhibition in D. pulex is unknown. The first objective of this study was to examine two possible mechanisms of metal inhibition. It was demonstrated that metal-induced inhibition in D. pulex is due neither to competitive inhibition at chemosensory binding sites on the neonate nor to a reduction in K(+) efficacy due to metal-binding to K(+) in the water column. Therefore, inhibition may occur along the signal transduction pathway downstream of kairomone reception by the mother. It is also unknown if inducible antipredator defenses are inhibited by metals among natural zooplankton populations. The second objective was to examine the effects of Cu and Ni on antipredator defenses in natural zooplankton. Ceriodaphnia spp., D. galeata mendotae, and D. retrocurva were exposed to Chaoborus predator kairomone in the presence and absence of Cu or Ni.Ceriodaphnia spp. and D. retrocurva were unable to respond to predator kairomone, while D. galeata mendotae was unaffected by the metals. This study narrows the scope of future research to uncover the specific mechanism of metal-impaired chemosensation in D. pulex. Additionally, results presented here will contribute towards a better understanding of the indirect effects of metal contamination in aquatic ecosystems. |
