PARENT SESSION
Poster Session 37: Toxicology and Disease
Thursday, August 11, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal
Metal tolerance acquisition in Daphnia pulex.
Shaw, Joseph, Glaholt, Stephen*,, Folt, Carol, Chen, Celia, Hamilton, Joshua,
ABSTRACT- A system perturbed by pollution often results in acquisition of tolerance by resident organisms resulting in individual physiological modifications (acclimation) and over time population restructuring. However, little is known about the mechanisms and costs associated with tolerance. Thus, we conducted both short-term (toxicity) and chronic(life-table) tests to explore differences in individual survivorship and population effects of naive vs. metal-acclimated populations of D. pulex. For these studies two metal-acclimated populations of D. pulex were developed by continuous exposure to cadmium concentrations (1 to 2.5 ug/L) for over 30 generations (>1 yr) in the laboratory. Toxicity tests (48-h) revealed that cadmium acclimated Daphnia compared to their naive counterparts (Daphnia not pre-exposed to metal) exhibit increased tolerance (i.e. higher survivorship) when exposed to cadmium, zinc, and silver but were not cross-tolerant to arsenic. Since cadmium/zinc and silver are accumulated by different pathways, these results suggest that altered uptake is not responsible for the metal tolerant phenotype. Rather they hint at a role of the metal binding protein, metallothionein (MT) in this phenomenon since these metals are potent inducers of MT, whereas, arsenic is not known to stimulate MT expression. At the population level, chronic studies (21-d) revealed that in the presence of cadmium (1 and 2.5 ug/L), metal acclimated populations had greater net reproductive output compared to naive populations. However, these patterns were reversed in control conditions as naive outperformed metal-acclimated Daphnia, suggesting there is a physiological cost associated with tolerance. In addition, the metal tolerant phenotype was rapidly lost (< 2 generations) following removal from metal. Collectively, these results demonstrate how stressors can be both advantagous and costly at the individual and population level.
Key words: Daphnia pulex, stress, metal, acclimation