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PH08 Metals in the Environment: Aquatic Biological Perspectives
(PH082) Evolution of cadmium tolerance in Daphnia magna during multigenerational exposure.
Guan, R1, Wang, WX1, 1 The Hong Kong University of Science and Technology, Hong Kong, China
ABSTRACT- A cadmium exposure (3g L-1) experiment was conducted for six successive generations to investigate the responses to chronic cadmium stress in the freshwater cladoceran, Daphnia magna. We observed a two-stage accumulation of cadmium. Within the first 3-4 generations, the Cd contents in the exposed daphnids (12 days old) increased gradually over generations, however, they decreased in the subsequent generations. Within the first 5 generations (F1-F5), there was no significant difference in the ingestion rate of the cadmium-treated animals. Since the ingestion rate was considered as a sensitive biomarker for the toxic effect of chemicals in cladocerans, the tolerance evolved in the exposed daphnids within the first 3-4 generations and but disappeared afterwards. The corresponding variations in the Cd assimilation efficiencies from the dietary phase and in the inductive responses of detoxifying metallothioneins (MTs) accounted partially for the observed tolerance development to Cd. These parameters provided important information for the potential bioavailability of Cd to the long-term exposed daphnids. Recovery from Cd exposure was examined in the F3 and F5 generations. When the maternal exposed neonates were grown in Cd-free water for 12 days, their growth performance, ingestion rate and MT induction only partially recovered, while the assimilation and accumulation of Cd were comparable to the control group. The rapid recovery of Daphnia magna from Cd-exposure suggests the high potential for ecological restoration from Cd pollution. Our results showed that the resistance evolution of Daphnia magna to Cd was not simple, especially when long-term exposure was involved. The increased tolerance developed within the first several generations might not be maintained, and the animals may become even more sensitive to Cd stress in subsequent generations.
Key words: cadmium, Daphnia magna, long-term exposure, tolerance evolution
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