The regulation of calcium in Daphnia magna reared in different calcium environments

Abstract

The specific content, dissolved uptake rate, dietary assimilation efficiency (AE), and efflux rate constant (k e ) of calcium (Ca) were quantified in juvenile (4-d) and adult (10-d) Daphnia magna cultured in low (0.5 mg L 21 )-and high (50 mg L 21 )-Ca environments using a radiotracer technique. Daphnids raised in the high-Ca environment had higher Ca contents than did those raised in the low-Ca environment, and juvenile daphnids had higher Ca contents than adults. Uptake from solution was the dominant source (97-100%) of Ca for daphnids. The maximum influx rate (J max ) was higher in juvenile daphnids (3.24-4.10 mg g dry weight [wt] 21 h 21 ) than in adults (1.51-1.62 mg g dry wt 21 h 21 ), while the influx rates were comparable in different Ca environments. The halfsaturation concentration (K m ) was 2.51-5.58 mg L 21 . The AEs of Ca declined exponentially with increases in food concentrations, and lower AE was observed in the higher Ca environment. The k e of Ca (0.83-1.98 d 21 ) was the highest among the elements whose k e had been quantified in D. magna, and it was 1.8-2.4 times higher in the high-Ca environment. Excretion into water was the dominant route (60-85%) of Ca release from daphnids; another 15-40% of Ca was lost as molts. The regulation of Ca in daphnids is mainly accomplished through adjusting their efflux but not their influx of Ca; their regulation ability is very limited, which may lead to a poor performance in daphnids in Ca-deficient water.

Calcium influence on phosphorus regulation in Daphnia magna: implications for phosphorus cycling

“…The release of P contained in the molting fluid was another possible explanation (Peters & Rigler 1973). A higher release rate during molting was also observed for Ca (Tan & Wang 2009), again suggesting the association of P and Ca in the molting process.To conclude, Daphnia magna living in a higher Ca environment had a lower specific P content, and there was a negative relationship between P and Ca contents. Therefore, Ca concentration should be considered when comparing the P content of daphnids collected from different localities.…”

“…The actual Ca concentrations were measured at the beginning and end of all experiments, and the average values matched well with the nominal concentrations (see Table 1). Because water is the principal source of Ca for Daphnia magna (Tan & Wang 2009), algae cultured in 0.5 mg Ca l -1 WC medium were used for all treatments in all experiments in order to avoid any difference in food.…”

“…(from < 2 to >10% dry wt; , the variation in P content is relatively restricted, with most observations lying within the range of 1.1 to 1.7% of dry wt (Hessen 1990). Ca content in daphnids is mainly dependent on the aqueous Ca level because water is the dominant source of Ca for daphnids (Tan & Wang 2009). In contrast, P is mainly assimilated from food, and daphnids can be cultured in a P-free medium (Ferrão-Filho et al 2007).…”

Regulation of sodium and calcium inDaphnia magnaexposed to silver nanoparticles

“…Whether AgNPs have similar effects on the Na flux and the underlying mechanism is still not known. In addition, daphnids require a large amount of Ca during their life cycle [19]. Calcium regulation may play an important role not only in molting but also in other capacities such as nerve function.…”

“…Calcium regulation may play an important role not only in molting but also in other capacities such as nerve function. It was found that nanoparticles could affect the Ca content in cell lines and cause an abrupt increase of both extracelluar and intracellular Ca influx [19]. Whether AgNPs can affect the Ca homeostasis and regulation in daphnids is still unknown.…”