title: Variation in malathion sensitivity among populations of Blanchard's cricket frogs (Acris blanchardi) and implications for risk assessment.
abstract: Intraspecific variability in contaminant sensitivity could undermine risk assessments for nontarget organisms such as amphibians. To test how amphibian populations vary in tolerance to anticipated lethal and sublethal exposures to a pesticide, we exposed Blanchard's cricket frogs (Acris blanchardi) from 3 populations across a broad portion of their range to the insecticide malathion. Exposure in mesocosms to a nominal concentration of 1 mg/L (measured concentrations at 1 h and 24 h postaddition of 0.160 mg/L and 0.062 mg/L, respectively), a realistic direct-overspray scenario, reduced survival to metamorphosis by 43% relative to controls and revealed variation in tolerance among populations. Survival ranged from 74% for the most tolerant population to 18% for the least tolerant population, a 4.1-fold difference. Mass at metamorphosis and time to metamorphosis were unaffected. Although malathion reduced zooplankton abundance, it did not alter food resources (periphyton or phytoplankton relative abundance), or a suite of water-quality variables (pH, temperature, and dissolved oxygen). A 96-h time-to-death assay designed to isolate direct, lethal effects also revealed variation in tolerance among populations. Time to death (mean ± standard error) ranged from 2.4 ± 0.18 h for the least tolerant population to 17.8 ± 4.72 h for the most tolerant population, a 7.4-fold difference. However, relative sensitivities of populations differed in the mesocosm and laboratory studies, which differed in exposure concentrations, suggesting that populations tolerant of high concentrations can be more sensitive to lower concentrations. We suggest that direct overspray could reduce larval survival in the field for this species. Studies assessing the role of contaminants in declines or extrapolating to untested populations, especially across large geographical regions, should quantify the range of intraspecific variation. Risk assessors could address intraspecific variability directly by using an intraspecific uncertainty factor. Environ Toxicol Chem 2017;36:1917-1923. © 2016 SETAC.
authors.affiliation: Department of Biology, Miami University, Oxford, Ohio, USA.
authors.forename: Tyler D
authors.initials: TD
authors.lastname: Hoskins
authors.affiliation: Department of Biology, Miami University, Oxford, Ohio, USA.
authors.forename: Michelle D
authors.initials: MD
authors.lastname: Boone
mesh_terms: D000818:Animals; D001001:Anura / Q000254:growth & development / Q000502:physiology; D006863:Hydrogen-Ion Concentration; D007306:Insecticides / Q000633:toxicity*; D007814:Larva / Q000187:drug effects / Q000254:growth & development / Q000502:physiology; D016014:Linear Models; D008294:Malathion / Q000633:toxicity*; D008675:Metamorphosis, Biological / Q000187:drug effects*; D018570:Risk Assessment; D013696:Temperature; D014874:Water Pollutants, Chemical / Q000737:chemistry / Q000633:toxicity*; D015048:Zooplankton / Q000187:drug effects / Q000254:growth & development
chemical_list: D007306:Insecticides; D014874:Water Pollutants, Chemical; D008294:Malathion
keywords: Amphibians; Ecotoxicology; Organophosphates; Risk assessment