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Presented at the NABS Annual meeting, Pittsburgh, Pennsylvania, 2002
in Ecotoxicology
LOW-LEVEL PESTICIDE EFFECTS ON DAPHNIA MAGNA GROWTH AND REPRODUCTION.
D.R. Kashian and S.I. Dodson. Zoology Department, University of Wisconsin, Madison, WI 53706
Daphnia population growth rates may be affected by low-level pesticide contamination resulting in detrimental ecological effects on invertebrate populations. We examined the pesticides 2,4-D, acetochlor, chlorsulfuran, cyanazine, o,p¨-DDT, p,p¨-DDE, metolachlor, metribuzin, Di-n-butyl phthalate, dimilin and toxaphene at ecologically relevant concentrations ranging from 0.01 to 100 レg/L. Short-term assays (6 days) examined effects on adult female Daphnia and their offspring; long-term assays examined daily effects on growth, fecundity, and offspring sex of Daphnia over its lifespan. Pesticide effects on several population parameters were apparent. Acetochlor (100 レg/L) significantly decreased Daphnia growth rate (p=0.04), and cyanazine exposure (100 レg/L) significantly reduced clutch sizes (p=0.04). Dimilin concentrations as low as 0.01 レg/L significantly increased mortality. Toxaphene (50 レg/L) doubled male production resulting in fewer asexually-reproducing females (p=0.02). Toxaphene also significantly decreased clutch size by 24% and adult size by 5% (p=0.01). Thus, pesticide contamination may indirectly affect Daphnia population growth rates by influencing clutch size, maturation time, and the proportion of asexually-reproducing females. Maintaining viable Daphnia populations is important because Daphnia play a key ecological role in surfaces waters, in that they are often the dominant herbivores and aid in the transfer of energy from autotrophs to the top of the food web.
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