title: Multiple environmental stressors elicit complex interactive effects in the western fence lizard (Sceloporus occidentalis).
abstract: Evaluation of multiple-stressor effects stemming from habitat degradation, climate change, and exposure to chemical contaminants is crucial for addressing challenges to ecological and environmental health. To assess the effects of multiple stressors in an understudied taxon, the western fence lizard (Sceloporus occidentalis) was used to characterize the individual and combined effects of food limitation, exposure to the munitions constituent 2,4,6-trinitrotoluene (TNT), and Plasmodium mexicanum (lizard malaria) infection. Three experimental assays were conducted including: Experiment I--TNT × Food Limitation, Experiment II--Food Limitation × Malaria Infection, and Experiment III--TNT × Malaria Infection. All experiments had a 30 day duration, the malaria treatment included infected and non infected control lizards, food limitation treatments included an ad libitum control and at least one reduced food ration and TNT exposures consisting of daily oral doses of corn oil control or a corn oil-TNT suspension at 5, 10, 20, 40 mg/kg/day. The individual stressors caused a variety of effects including: reduced feeding, reduced testes mass, anemia, increased white blood cell (WBC) concentrations and increased mass of liver, kidney and spleen in TNT exposures; reduced cholesterol, WBC concentrations and whole body, testes and inguinal fat weights given food limitation; and increased WBC concentrations and spleen weights as well as decreased cholesterol and testes mass in malaria infected lizards. Additive and interactive effects were found among certain stressor combinations including elimination of TNT-induced hormesis for growth under food limitation. Ultimately, our study indicates the potential for effects modulation when environmental stressors are combined.
authors.affiliation: Health Effects Research Program, Toxicology Portfolio, U.S. Army Institute of Public Health, Aberdeen Proving Ground, MD 21010-5403, USA. craig.a.mcfarland@us.army.mil
authors.forename: Craig A
authors.initials: CA
authors.lastname: McFarland
authors.forename: Larry G
authors.initials: LG
authors.lastname: Talent
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Quinn
authors.forename: Matthew A
authors.initials: MA
authors.lastname: Bazar
authors.forename: Mitchell S
authors.initials: MS
authors.lastname: Wilbanks
authors.forename: Mandana
authors.initials: M
authors.lastname: Nisanian
authors.forename: Robert M
authors.initials: RM
authors.lastname: Gogal
authors.forename: Mark S
authors.initials: MS
authors.lastname: Johnson
authors.forename: Edward J
authors.initials: EJ
authors.lastname: Perkins
authors.forename: Kurt A
authors.initials: KA
authors.lastname: Gust
mesh_terms: D000818:Animals; D001774:Blood Chemical Analysis; D002140:California; D004032:Diet; D004305:Dose-Response Relationship, Drug; D004781:Environmental Exposure; D004784:Environmental Monitoring; D004785:Environmental Pollutants / Q000378:metabolism / Q000633:toxicity; D006403:Hematologic Tests; D007124:Immunoenzyme Techniques; D008099:Liver / Q000378:metabolism; D008116:Lizards / Q000469:parasitology* / Q000502:physiology*; D008288:Malaria / Q000469:parasitology*; D008297:Male; D009929:Organ Size; D010961:Plasmodium / Q000502:physiology; D013094:Spermatozoa / Q000502:physiology; D013739:Testosterone / Q000378:metabolism; D014303:Trinitrotoluene / Q000378:metabolism / Q000633:toxicity*
chemical_list: D004785:Environmental Pollutants; D014303:Trinitrotoluene; D013739:Testosterone