Genetic Variation in Laboratory and Field Populations of the Midge, Chironomus Tentans Fab.: Implications for Toxicology

Abstract

Chironomus tentans larvae are used extensively in toxicoiogical bioassays. Gel electrophoresis was performed on seven laboratory populations and a wild population of C. tentans. Direct count heterozygosity was significantly different between wild and laboratory populations, as well as among laboratory populations. Percent polymorphic loci demonstrated the same trends but were marginally nonsignificant. The wild midge population had seven unique alleles and a significantly higher level of heterozygosity. Despite these differences the wild population was genetically similar to laboratory populations. The impact of significant differences in Chironomus genetic variability on toxicological bioassays is discussed.

Molecular and genetic ecotoxicologic approaches to aquatic environmental bioreporting.

“…Chironomus species usually account for at least 50% of the combined macroinvertebrate species composition on any given freshwater ecosystem (97). Chironomids are common and have an holarctic distribution, they are relatively sedentary and thus representative of local conditions, and larvae may accumulate metals in a manner directly proportional to environmental conditions (41,57,98 (57), and Harrahy et al (98). A. aegypti were reared as described by Raymes-Keller et al (99).…”

“…A. aegypti were reared as described by Raymes-Keller et al (99). The basic protocol was to expose C. tentans or A. aegvpti larvae to predetermined sublethal doses of heavy metals (41,57,98). Each experiment was conducted in duplicate; 50 to 100 fourth instar larvae were placed in receptacles filled with 200 ml dechlorinated tap water containing either 50 or 500 ppb Cd (or other metals such as Hg) and Cu, or their binary and trinary combinations, in the case of A. aegypti, or no metal.…”

“…After exposure larvae were harvested and nucleic acids were isolated. The challenge doses and regimens were selected based on the published data on the biotoxicologic effect of Cd on C. tentans (41,57,98) and our data demonstrating the effect of Cd on A. aegypti (99).…”

“…Interspecific differences in aquatic arthropod populations have been demonstrated in response to heavy metal insult associated with the AR-CGSS. There are shifts in benthic community composition and reduced species diversity at sites located downstream from the CGSS (1,29 (15,16,(29)(30)(31)(32)(33)(34)(35) and for environmental bioreporting (36)(37)(38)(39)(40)(41)(42)(43)(44)(45)(46)(47)(48)(49)(50). Chironomids, mayflies, and caddis flies have common attributes that make them attractive for bioreporting: they are commonly found in most aquatic systems; they are relatively sedentary and thus representative of local conditions; they are benthic and thus closely associated with sediments; and they accumulate metals in a manner directly proportional to environmental conditions (33).…”

Genetic differentiation among laboratory populations of Hyalella azteca: Implications for toxicology

“…It has also been demonstrated that conditions in the laboratory environment may cause unanticipated alterations in the population's genetic structure such as changes in allele frequency, loss of alleles, and diminished heterozygosity. These changes could result from founder events, genetic drift, nonrandom mating, and artificial selection [1].…”