2002 Progress Report: Models and Mechanisms: Understanding Multiple Stressor Effects on an Amphibian Population

EPA Grant Number: R829086
Title: Models and Mechanisms: Understanding Multiple Stressor Effects on an Amphibian Population
Investigators: Palmer, Brent D. , Elskus, Adria , Sih, Andy , Shepherd, Brian , Crowley, Philip
Institution: University of Kentucky , University of California - Davis
Current Institution: University of Kentucky
EPA Project Officer: Packard, Benjamin H
Project Period: August 1, 2001 through July 31, 2004 (Extended to November 25, 2005)
Project Period Covered by this Report: August 1, 2001 through July 31, 2002
Project Amount: $522,832
RFA: Wildlife Risk Assessment (2001) RFA Text |  Recipients Lists
Research Category: Environmental Justice , Biology/Life Sciences , Ecological Indicators/Assessment/Restoration , Aquatic Ecosystems


The objective of this research project is to investigate the impact of multiple real-world stressors on a model amphibian population. The overall hypothesis is that multiple stressors can interact to generate complex detrimental effects on populations, and that these effects can be much more severe than those produced by any single stressor. In this multi-disciplinary study, we are investigating toxicology, physiology, behavioral ecology, and ecological modeling, with the goal of assessing long-term effects of multiple real-world stressors (chemicals, predators, food, drought) on amphibian populations. The specific objectives of this research project are to: (1) build and implement a spatially-explicit, individual-based population model; (2) conduct experiments to measure the effects of multiple stressors on parameters that enter into the model (e.g. survival, fecundity, growth, extinction rates); and (3) measure endocrine and physiological variables to investigate potential mechanisms underlying the effects of multiple stressors on the parameters that enter into the model.

Progress Summary:

In Year 1 of the project, we investigated the interactions of environmentally relevant concentrations of contaminants with ecological stressors. First, we examined the effects of 37-day embryo/larval exposure to the agrichemicals atrazine, carbaryl, endosulfan, and octylphenol (nominal concentrations: 4-400, 0.5-50, 0.1-10, and 5-500 ppb, respectively) on streamside salamanders, Ambystoma barbouri, in the presence and absence of food. Results are for comparisons with solvent controls and significant effects were only found for the highest agrichemical concentrations for all studies. Octylphenol delayed hatching, but none of the agrichemicals significantly affected embryo survival; however, larval survival was reduced by carbaryl, endosulfan, and octylphenol, and growth rates were reduced by endosulfan and octylphenol. Significantly more carbaryl, endosulfan, and octylphenol tanks had larvae with limb deformities. Endosulfan and octylphenol decreased larval activity, and atrazine- and endosulfan-treated salamanders exhibited skittishness in response to a vibration stimulus. Agrichemicals inhibited the decrease in refuge use and the increase in activity stimulated by hunger. More indepth investigations on the effects of atrazine (actual concentrations: 0-200 ppb) and food abundance (limited and unlimited food) were conducted on A. barbouri from embryo to metamorphosis. In general, atrazine did not statistically interact with food abundance, and atrazine concentration was correlated positively with effect size. Atrazine decreased embryo survival and increased time to hatching and variation in hatching day. This greater hatching variation amplified size variation, which facilitated larval cannibalism. Increasing atrazine concentrations decreased refuge use and activity. Both food restriction and atrazine reduced larval growth and metamorph size, despite atrazine having no effect on feeding rates. Food limitation delayed metamorphosis while atrazine shortened the larval period. Because reduced growth and smaller size at metamorphosis can lower terrestrial survival and lifetime reproduction, resource limitations and ecologically realistic concentrations of atrazine have the potential to cause or exacerbate amphibian declines in impacted systems.

Future Activities:

Future activities will include both physiological and behavioral studies, as well as completion and validation of the spatially explicit individual-based population model. We have collected this year's specimens and are treating them with three levels of atrazine. The larvae will be subjected to a number of behavioral trials, including predator-avoidance, drift, osmoregulation, and genotypic influence on behavioral traits. Physiological studies will investigate the mechanisms of action by focusing on endocrine control and P450 metabolism.

Journal Articles on this Report : 1 Displayed | Download in RIS Format

Other project views: All 25 publications 5 publications in selected types All 5 journal articles
Type Citation Project Document Sources
Journal Article Rohr JR, Elskus AA, Shepherd BS, Crowley PH, McCarthy TM, Niedzwiecki JH, Sager T, Sih A, Palmer BD. Lethal and sublethal effects of atrazine, carbaryl, endosulfan, and octylphenol on the streamside salamander (Ambystoma barbouri). Environmental Toxicology and Chemistry 2003;22(10):2385-2392. R829086 (2002)
R829086 (2003)
R829086 (Final)
  • Abstract: SETAC Journals Abstract
  • Supplemental Keywords:

    behavior, endocrine disruption, water, watersheds, sensitive populations, dose-response, ecological effects, toxics, aquatic, conservation, ecology, climate change, Kentucky, KY., RFA, Health, Scientific Discipline, Air, Ecosystem Protection/Environmental Exposure & Risk, Aquatic Ecosystems & Estuarine Research, exploratory research environmental biology, wildlife, Ecosystem/Assessment/Indicators, climate change, Air Pollution Effects, Aquatic Ecosystem, Susceptibility/Sensitive Population/Genetic Susceptibility, Monitoring/Modeling, Ecological Effects - Environmental Exposure & Risk, Environmental Monitoring, genetic susceptability, Ecological Risk Assessment, Atmosphere, predicting risk, sensitive populations, anthropogenic stress, ecological exposure, demographic data, stressors, watersheds, endocrine disruption , amphibians, dose-response, endocrine disrupting chemical, exposure, amphibian, endocrine disruptors, modeling, multiple stressors, Wildlife Risk Assessment, animal models, salamander eggs, ecosystem stress, watershed assessment, ecological response, toxics, environmental hazard exposures, modeling ecosystems, amphibian population

    Progress and Final Reports:

    Original Abstract
  • 2003 Progress Report
  • 2004
  • 2005
  • Final Report