| Environmental Health Issues Stanley I. Dodson1 and Takayuki Hanazato2 1Department of Zoology, University of Wisconsin, Madison,
Wisconsin; 2National Institute for Environmental Studies, Onogawa,
Tsukuba, Japan Abstract
Because of their trophodynamic role, small invertebrates are often critical components of ecosystems. An especially important group of freshwater invertebrates is the water fleas of the genus Daphnia. These animals are often the dominant herbivores in lakes and ponds. They play a key role in determining water clarity (by grazing on algae) and they are an important part of the diet of fish. Natural chemical signals (kairomones) produced by predators affect the development, life history strategy, and behavior of zooplankton. Laboratory studies of anthropogenic chemicals that have biological activity (xenobiotics) , such as the insecticide carbaryl, have demonstrated effects of concentrations in the 1 to 5 ppb range on Daphnia development, growth rate, and swimming behavior in our laboratory experiments. Low concentrations of carbaryl inhibit growth and reproduction and delay maturation, whereas survivorship was not effected. These sublethal exposures to carbaryl reduced Daphnia population growth rate (productivity) by about 15% (at 5 ppb) , enough to have significant ecological effects on the rest of the lake community. The insecticide carbaryl showed synergistic interactions with natural chemicals associated with predators (kairomones) that modify Daphnia development and life history characteristics. In addition, there were complex synergisms between carbaryl, the predator odors, and oxygen concentration (low oxygen concentration can be either a natural environmental stress or an anthropogenic stress) . Daphnia produce males facultatively, usually in late fall ; at other times, reproduction is asexual. There is some evidence from long-term field studies that the maximum frequency of males has declined since the 1940s, when estrogen-mimicking xenobiotics first appeared in lakes. A decrease in sexual recombination will result in maladapted Daphnia relative to their constantly changing environment. -- Environ Health Perspect 103(Suppl 4) :00-00 (1995) Key words: Daphnia, Chaoborus, carbaryl, kairomone, development, life history, swimming behavior, estrogenic, sex ratio, fitness
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