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Abstract
Human activities have radically altered environments globally. One of the prominent, but less visible impacts of human activities is the chemical contamination of aquatic habitats. Aquatic organisms are often highly susceptible to changes in the chemical composition of the water they rely on for survival. This dissertation investigates mechanisms by which a highly susceptible species, the southern toad (Anaxyrus terrestris), copes with the chronic contamination of wetlands with toxic trace elements. Using an interdisciplinary approach, I assessed the evidence for the evolution of adaptive tolerance in a population living in a contaminated habitat for >60 years, physiological mechanisms underlying tolerance, and the role of gut microbial communities in mediating toxicity. I found evidence of adaptive tolerance to trace element stressors corresponded with physiological divergence in response to these chemical stressors and life history trade-offs in their absence. Gut microbial communities in metamorphic toads were altered by rearing in the contaminated environment, which was associated with greater abundances of potentially pathogenic bacterial genera. Further, the richness and structure of gut communities were related to within environment variation in life history traits and accumulation of toxic trace elements. Lastly, I examined larval metal tolerance across toad populations varying in their history of contaminant exposure to assess whether adaptive tolerance to trace elements observed in the field study was common across the landscape. Overall, offspring from trace element contaminated sites were more tolerant to aquatic metal exposure, but the extent of this tolerance depended on the specific nature of the contamination across sites. These results suggest the potential for evolutionary rescue to mitigate some negative effects associated with environmental contaminants, but not without costs.