Population responses of daphnia to long-term exposure to cadmium
Milwaukee, Wis., Univ. of Wisconsin, Diss., 1980
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Tag hinzufügen | Zusammenfassung: | Milwaukee, Wis., Univ. of Wisconsin, Diss., 1980 The effects of acute and chronic exposure to Cd were assessed on four strains of Daphnia isolated from naturally occurring populations. The 96hrEC(,50) of cadmium in L. Michigan water for D. galeata-mendotae (L. Michigan), D. galeata-mendotae (L. Huron), D. pulicaria (Crystal Lake Wi.), D. pulicaria (L. Michigan) at 15(DEGREES)C was 192, 152, 310 and 351 (mu)g Cd/l respectively. All four strains exhibited similar responses to Cd at 15(DEGREES)C. The time to maturation and the number of days between broods were unaffected by Cd. The average brood size of the strains as ordered above was reduced by approximately half upon exposure to 10, 50, 100 and 200 (mu)g Cd/l with control brood sizes of 3.0 4.0, 3.2 and 5.5 respectively. For the strains as ordered above, the intrinsic rate of increase, r, was influenced mainly by mortality of pre-reproductive young daphnids within the cohorts and was inversely proportional to lnCd} (except inversely linear for D. pulicaria (Crystal Lake) through 50, 25, 100 and 150 (mu)g Cd/l. The Cd concentration at which r = 0 was estimated to be 57, 77, 124 and 219 (mu)g Cd/l respectively. The average r for cohorts of D. pulicaria (L. Michigan) which were subjected to chronic Cd stress of 0, 1, 10 or 150 (mu)g Cd/l for 10 successive generations at 15(DEGREES)C was 0.1405, 0.1234, 0.1146, 0.1028 and 0.0560 respectively. The absence of a trend in the values of r over 10 generations indicated that neither acclimation or increased sensitivity to Cd occurred in the daphnids. No opportunity for genetic adaptation was provided during these experiments since all reproduction occurred parthenogenically. A reduction of 10% in average brood size was correlated with a reduction of 5% in feeding rate for chronic exposure to each 10-fold increase in Cd concentration from 0 ((TURNEQ)0.1) to 10 (mu)g Cd/l. Feeding rate was significantly reduced in daphnids exposed to 100 (mu)g Cd/l. The pattern of uptake of Cd in D. pulicaria suggests a two-compartment system. One probably represents an adsorption equilibrium between the exoskeleton and Cd in solution in the water. The other appears to be a function of simple diffusion of the metal into the animal followed by sequestration. The rate of accumulation of Cd within the daphnid was proportional to the Cd concentration in the water from 0.1 through 100 (mu)g Cd/l. An adult daphnid exposed to 100 (mu)g Cd/l for 30 days accumulated 14.5 ng Cd at a rate of 0.38 ng Cd/day. The half-life of Cd in the daphnids was 50 - 129 days. Cd-laden Daphnia did not shunt Cd from the body to the exoskeleton, nor to the offspring. |
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| Beschreibung: | 155 S. |