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.

Leukocyte Profiles for Western Fence Lizards,Sceloporus occidentalis, Naturally Infected by the Malaria ParasitePlasmodium mexicanum

“…However, the effect of such infections on leukocyte profiles is poorly known. Several studies on hematozoan infection in reptiles and amphibians have shown either changes in leukocyte densities or reductions in humoral components of the immune response when infected (Ujvari and Madsen, 2005;Bonadiman et al, 2010;Motta et al, 2011;Shutler and Marcogliese, 2011;McFarland et al, 2012). Although many hematozoan parasites are considered nonpathogenic (Brown et al, 2006;Jacobson, 2007;Stacy et al, 2011), some do result in a variety of physiological, reproductive, and behavioral changes (Schall, 2002;Ujvari et al, 2004;Amo et al, 2005;Ujvari and Madsen, 2005;Vardo-Zalik and Schall, 2008;Motta et al, 2011), and further examination of leukocyte alterations or other immune responses to these infections should clarify this parasite-host biology.…”

“…Experimentally infected male S. occidentalis display altered leukocyte profiles, but it is unknown whether this translates to what occurs naturally in this parasitehost system (McFarland et al, 2012), and what changes occur in female lizards has not been examined. We used a case-control study design where naturally infected lizards were paired with noninfected control lizards based on sex, size, tail status, and the presence-absence of ectoparasites and the hemoparasite S. occidentalis.…”

“…Of the studies examining reptilian hematological parameters and hematozoan infections published to date, a marked change in white blood cell (WBC) concentrations for infected reptilian hosts has sometimes been noted (Silva et al, 2004;Bonadiman et al, 2010;McFarland et al, 2012). For example, in Ameiva ameiva lizards infected with a hemogregarine parasite, lizards with higher parasite loads had significantly higher levels of monocytes in their blood (Bonadiman et al, 2010).…”

“…Therefore, any immune response elicited by the lizard may be to reduce, rather than eliminate infection. Although much work has been conducted on the relationship between the parasite and its host (Schall, 1996(Schall, , 2002Schall, 2008, 2009), there has been only one study examining the effect of malaria infection on leukocyte composition in S. occidentalis (McFarland et al, 2012); this work used experimental infections and used only male lizards. A further examination of naturally infected lizards is warranted as the stressors of captivity plus malaria infection could exaggerate the immune response observed in experimental studies (Davis et al, 2008).…”

Tissue distribution, metabolism and hepatic tissue injury in Chinese lizards (Eremias argus) after a single oral administration of lambda-cyhalothrin

“…To ensure that the corn oil was homogenously mixed with LCT, the dosing method was set up in steps (Suski et al, 2008;McFarland et al, 2012). LCT was first dissolved in methanol and then dispersed into the corn oil (methanol/oil ¼ 1/9, v/v, total volume 20 mL).…”