Selenium deficiency induced by zinc deprivation in a crustacean

Abstract

For intact daphnids reared in circumstances of controlled trace element exposure, one consequence of insufficient zinc (Zn) is an increased demand on the animal's pool of available selenium (Se). This demand is manifested by the type of cuticle deterioration associated with Se deficiency and by a depression of reproduction. In the presence of 25 parts per billion (ppb) Zn, 1 ppb Se eliminates these symptoms. In the absence of detectable Zn, 5 ppb Se eliminates overt cuticle damage and substantially increases reproduction. A shortening of life span resulting from Zn deprivation is not ameliorated by Se addition. We suggest that the interplay between Zn and Se concentrations reflects an underlying interplay between interdependent, but distinct, metabolic pathways; i.e., (for Se) glutathione peroxidase and (for Zn) Cu,Zn-superoxide dismutase-each offering protection against free radical damage. Because they are not necessarily localized in a given tissue, the key to recognition of such subtle, complex trace nutrient interactions has been use of intact animals in circumstances of control previously attainable only in tissue cultures.Little specific information concerning the trace element requirements of zooplankters exists. For example, although more than 100 eukaryotic enzymes have been shown to depend on zinc (Zn) (1), no certain proof that Zn is required by a Cladoceran has been published. This reflects more the limitations of the state of the art in animal culture than an absence of common eukaryotic enzymes in zooplankters. Extensive observation of healthy animals under explicit chemical conditions is necessary for determination of trace element requirements, and such observation has not been possible with zooplankters until recently (2).The significance of trace elements in the structuring of aquatic communities has long been acknowledged (3, 4). Yet, in the absence of secure data, only reasonable speculation about the requirements of a specific organism for a specific trace element or the effects on community structure of such requirements has been possible. There is great diversity among the trace element matrices found in various fresh waters. Of particular interest have been the influences on community structure of idiosyncratically low or high concentrations of single elements (5) or of sets of elements (6). As phytoplankton culture became more sophisticated and suitable chelators (7) fostered more qualitative and quantitative control of trace elements in cultures, absolute requirements for most of the trace elements currently identified as essential by nutritionists were recognized as essential for various phytoplankters (8). Zooplankton work has lagged behind.Reflecting the generalized absence of basic proofs of trace element essentiality for zooplankters, our original intent had been simply to withdraw Zn from both the food and ambient water and to produce symptoms of severe deficiency for the first time in a daphnid culture. However, a complex response, involving an induced selenium (Se) defi...

Dietary assimilation and elimination of Cd, Se, and Zn by Daphnia magna at different metal concentrations

“…Both Se and Zn are essential to Daphnia [9][10][11][12], and Cd has no known biological function in the animals. The three metals (Cd, Se, and Zn) considered are environmentally important metals/metalloids in aquatic systems.…”

Results of zinc deprivation in daphnid culture

“…Zinc deprivation of D. pulex results in a loss of cuticle integrity. This involves a relationship between the zinc status and the selenium status of the animal [20] and is often characterized in older animals by damage to appendages. Setae and rami appear to break at the joints.…”

“…First, in the initial zinc‐deprived generations, a loss of cuticle integrity was noted. This symptom was reminiscent of the results of selenium deprivation [21] and was in fact eliminated with additional selenium [20]. The elimination of this specific symptom in zinc‐deprived animals by addition of selenium supplements indicates that a selenium deficiency is induced by zinc deprivation.…”

Silver Deprivation Limits Fecundity and Survivability in the Freshwater Crustacean, Daphnia magna

“…The MS system, basic to demonstration of trace element deprivation in previous studies [7][8][9][10], was employed to rear test animals and their algal foods. The exposure of test animals to trace elements is controlled through these media, which are wholly defined, sensu stricto, and are comprised of inorganic salts (because it is a key to the interpretation of results, media constituent lists are included, Table 1), dissolved in a very-high-quality deionized/distilled water.…”