title: Variation in toxicity of a current-use insecticide among resurrected Daphnia pulicaria genotypes.
abstract: This study examined how genotypes of Daphnia pulicaria from a single population, separated by thousands of generations of evolution in the wild, differ in their sensitivity to a novel anthropogenic stressor. These genotypes were resurrected from preserved resting eggs isolated from sediments belonging to three time periods: 2002-2008, 1967-1977, and 1301-1646 A.D. Toxicity of the organophosphate insecticide chlorpyrifos was determined through a series of acute toxicity tests. There was a significant dose-response effect in all genotypes studied. Moreover, significant variation in toxicity among genotypes within each time period was detected. Importantly, a significant effect of time period on sensitivity to chlorpyrifos was found. Analysis of the median effect concentrations (EC50s) for genotypes within each time period indicated that the 1301-1646 genotypes were 2.7 times more sensitive than the 1967-1977 genotypes. This trend may be partially explained by microevolutionary shifts in response to cultural eutrophication.
authors.affiliation: Department of Zoology, Oklahoma State University, 501 Life Sciences West, Stillwater, OK, 74078, USA, adam.simpson@okstate.edu.
authors.forename: Adam M
authors.initials: AM
authors.lastname: Simpson
authors.forename: Punidan D
authors.initials: PD
authors.lastname: Jeyasingh
authors.forename: Jason B
authors.initials: JB
authors.lastname: Belden
mesh_terms: D000818:Animals; D005075:Biological Evolution; D004390:Chlorpyrifos / Q000633:toxicity*; D003621:Daphnia / Q000187:drug effects* / Q000235:genetics*; D004305:Dose-Response Relationship, Drug; D005838:Genotype; D007306:Insecticides / Q000633:toxicity*; D007928:Lethal Dose 50; D008910:Minnesota; D013997:Time Factors
chemical_list: D007306:Insecticides; D004390:Chlorpyrifos