title: Variation in sensitivity to cadmium among genetically characterized laboratory strains of the midge Chironomus riparius.
abstract: Estimating the extent of intraspecific variation in sensitivity to contaminant exposure is important in order to explain variation in the outcome of toxicity tests and to predict the effects of chemical stress on natural populations of plants and animals. However, only few studies provide evident data concerning intraspecific variation in life-history traits caused by a differential response to chemical stress. In this study, we compared the life-history response of six laboratory strains of the midge Chironomus riparius to cadmium exposure in a full life-cycle assay. In addition, the level of genetic variation in all strains was measured at five variable microsatellite loci. Several significant differences in life-history traits among the strains were observed in controls and cadmium treatments. The extent of variation among strains was largest at moderate cadmium concentration (0.42 mg Cd/kg dw). At increased Cd concentrations all strains showed similar levels of high mortality and reduced reproductive success. All strains exhibited considerable levels of genetic impoverishment compared to field populations. Strains with low genetic variation showed reduced fitness in the controls and were more susceptible to Cd exposure. For instance, no reproductive success in the lowest Cd treatment was observed for the strain with the lowest level of genetic diversity. In contrast, this Cd concentration had no negative effects on life-history traits of more variable strains. These results confirm recent findings, that inbreeding and reduced genetic variation influence the reaction of populations towards environmental stress. In addition, we show that the level of genetic variation and inbreeding directly influences the outcome of toxicity tests and contributes to the lack of reproducibility of test results among laboratories.
authors.affiliation: J.W. Goethe University, Institute of Ecology, Evolution and Diversity, Department of Ecology and Evolution, Siesmayerstrasse 70, D-60323 Frankfurt am Main, Germany. cnowak@senckenberg.de
authors.forename: Carsten
authors.initials: C
authors.lastname: Nowak
authors.forename: Andreas
authors.initials: A
authors.lastname: Czeikowitz
authors.forename: Christian
authors.initials: C
authors.lastname: Vogt
authors.forename: Matthias
authors.initials: M
authors.lastname: Oetken
authors.forename: Bruno
authors.initials: B
authors.lastname: Streit
authors.forename: Klaus
authors.initials: K
authors.lastname: Schwenk
mesh_terms: D000818:Animals; D002104:Cadmium / Q000633:toxicity*; D002683:Chironomidae / Q000187:drug effects* / Q000502:physiology; D005260:Female; D014644:Genetic Variation; D018895:Microsatellite Repeats / Q000235:genetics; D023421:Models, Animal; D012098:Reproduction / Q000187:drug effects; D014874:Water Pollutants, Chemical / Q000633:toxicity*
chemical_list: D014874:Water Pollutants, Chemical; D002104:Cadmium