Trace element deficiency in freshwater cladoceran Daphnia magna

Abstract

We conducted Cu, Se, and Zn deficiency-recovery experiments and measured a suite of biological parameters such as reproduction, mortality, morphology, and dietary assimilation in the freshwater cladoceran Daphnia magna. Whether Cd could substitute for Zn or Cu when the latter metals were deficient was also tested in this animal system. Significant reduction in reproduction was observed for the first generation (F0) of the Cu- or Zn-deficient daphnids, whereas Se deficiency only caused significant reduction in reproduction in the second generation (F1). A complete recovery of reproduction in F1 was observed when daphnids were transferred to Se- and Cu-sufficient conditions, but only partial recovery was found for Zn. There was no significant mortality for the Se- and Zndeficient daphnids in F0, but significant mortality was observed for the F1 Se-deficient and the F0 Cudeficient daphnids. No morphological defects were observed in the metal-deficient daphnids of F0. However, Se-deficient F1 showed bi-phased morphological defects of the cuticle and the second antenna. Cd could not substitute Cu or Zn in the D. magna biological requirements, but caused additional toxicity to the daphnids. A high dietary Zn assimilation efficiency was found in the Zn-deficient daphnids, whereas dietary Se assimilation was comparable between the Se-deficient and Se-sufficient daphnids, suggesting that daphnids possessed a stronger homeostatic ability for Zn than for Se. Our study demonstrated that daphnids responded differently to deficiencies of different essential trace elements, which was unlikely to have been controlled by their biokinetics (i.e. dietary assimilation). © Inter-Research 2008.