W7 AM Acclimation / Adaptation of Animals to Metals: Resistance, Tolerance, and Cost
Wednesday, 16 November 2005: 8:00 AM - 11:40 AM in 327-329

(MUY-1117-541526) Multi-generation zinc acclimation and cost of tolerance in Daphnia magna.

Muyssen, B.¹, Janssen, C.¹, ¹ Ghent University, Laboratory of Environmental Toxicology and Aquatic Ecology, Ghent, Belgium

ABSTRACT- The acclimation potential of Daphnia magna to zinc was investigated by means of an extensive laboratory multi-generation study. In the first generation exposed to concentrations up to 195 g Zn²⁺/L reproduction was stimulated. After 5 generations, however, an optimal concentration range could be observed at concentrations of 2 to 19 g Zn²⁺/L with deficiency and toxicity symptoms outside this range. The same trends were found for carapax length and energy reserves. Acclimated organisms were a factor of 3 more tolerant in acute toxicity tests than non-acclimated daphnids. Also in chronic tests it was found that 8th generation daphnids acclimated to concentrations equal or higher than 0.7 g Zn²⁺/L and exposed to 86 g Zn²⁺/L performed significantly better than organisms acclimated to lower concentrations, except for zinc-deprived animals in which reproduction was stimulated. In an additional study in which D. magna was acclimated to environmentally realistic zinc concentrations ranging from 0.02 to 74 g Zn²⁺/L acute nor chronic zinc tolerance was increased. However at test concentrations below the 21dEC50, acclimation to 6 to 22 g Zn²⁺/L did significantly increase reproductive rates, which corresponds to the previously established optimal range. Generally in toxicity testing, acclimation (deliberate or not) of test organisms should be taken into account and especially the use of zinc-deprived test organisms should be avoided as this renders organisms unnaturally sensitive. Finally, in an attempt to unravel processes underlying chronic zinc toxicity in D. magna, it was found that organisms show recovery of acute zinc toxicity between day 7 and day 14 of exposure. In surviving animals, the body calcium content was restored as well as filtration rate, energy reserves and reproduction. The use of genomic tools will help to further elucidate acclimation mechanisms.

Key words: acclimation, sensitivity, deficiency, energy