Ecological And Physiological Effects Of Environmental Stressors Across Life Stages In Amphibians PDF Download

Understanding the effects of environmental stressors includes identifying how stressors affect individual physiology and ecological communities. Considering carry-over effects, effects from one life-stage persisting into later life-stages, can further reduce the chances of under- or over-estimating the effects of environmental stressors. I investigated the effects of two environmental stressors on amphibian physiology across life-stages including direct and indirect effects. I first investigated road salt. Road salt, a de-icing agent used on highways, can spread up to 1km in wetlands during snowmelt. It may be particularly important for early breeding amphibians like wood frogs (Rana sylvatica). Road salt significantly increased larval frog growth and algal biomass which was likely due to an indirect effect of salt decreasing zooplankton abundance, an algal competitor of frogs. A second experiment found despite increased larval growth, exposure to road salt caused juvenile frogs to have higher mortality in low-density terrestrial environments. The second stressor I investigated was Artificial Light At Night (ALAN). ALAN reduced metamorphic duration of American toads (Anaxyrus americanus) and periphyton biomass but did not affect the colonization of toad predators. These results suggested the effects of ALAN are mediated through direct rather than indirect effects. Extending this experiment found juvenile growth was reduced by juvenile-stage exposure to ALAN. Increased juvenile activity, specifically the lack of suppressed nocturnal activity, likely reduced juvenile growth of individuals housed with ALAN. Furthermore, carry-over effects were also present; larval-stage ALAN marginally increased juvenile activity. In the final experiment, I added an additional stressor: predation. Predators reduced toad survival and mass, regardless of ALAN. This suggests ALAN did not increase predator consumption of toads. Neither predators nor ALAN affected corticosterone production in the tadpole or metamorph life-stages but larval-stage ALAN increased corticosterone production in juvenile toads. These experiments demonstrated environmental stressors can have direct and indirect effects. Furthermore, larval stage stressors can carry-over and affect later life-stages even if that stressor is no longer present. Future environmental stressor studies should investigate direct and indirect effects together and extend experiments beyond a single life-stage. As demonstrated here, failure to do so may under-estimated the effects of these environmental stressors.