Year of Award

2021

Document Type

Dissertation

Degree Type

Doctor of Philosophy (PhD)

Degree Name

Fish and Wildlife Biology

Department or School/College

W.A. Franke College of Forestry and Conservation

Committee Chair

Creagh W. Breuner

Commitee Members

Blake R. Hossack, Erica J. Crespi, Lisa A. Eby, Joshua J. Millspaugh

Keywords

amphibians, conservation physiology, corticosterone, salinity, wastewaters

Abstract

Salinity is a persistent anthropogenic contaminant that negatively effects freshwater species, communities, and ecosystems. High-salinity wastewaters from energy extraction (wastewaters) and road salts are major contributors to increased salinity (NaCl; sodium chloride), but most studies focus on effects of NaCl roads salts. Amphibians are particularly vulnerable to contaminants such as increased salinity because of their porous skin, dependence on freshwater, and poor osmoregulatory capacity. We investigated the relative effects of wastewaters and NaCl on three species of larval amphibians with acute toxicity experiments (Chapter 1). Effects of wastewaters on larvae were predominantly due to high concentrations of NaCl and both had negative effects on survival and growth of larvae. Information on the effects of salinity on amphibian eggs is limited. Therefore, we used chronic toxicity experiments to test the relative effects of wastewaters and NaCl on eggs and larvae of two amphibian species (Chapter 2). Effects of NaCl and wastewaters were comprehensive, but similar, and negatively influenced hatching of eggs and survival, growth, and behavior of larvae. Larvae that survived exposure to increased salinity were smaller, suggesting a growth-survival tradeoff. We tested the influence of salinity on growth, survival, corticosterone (CORT; a steroid hormone) responses, and tradeoffs among traits of a larval amphibian (Chapter 3). By experimentally suppressing CORT signaling, we demonstrate that CORT mediated a growth-survival tradeoff. Suppressing CORT reduced survival further than for controls, but effects of salinity on growth and development were attenuated. Because CORT enhanced survival and influenced fitness-related traits following exposure to salinity, it could be a marker of physiological stress. Therefore, we evaluated whether CORT could be used as a biomarker of individual and population condition for freeliving larval amphibians exposed to wastewaters (Chapter 4). We provide only weak evidence that we could detect changes in waterborne CORT for free-living amphibians exposed to salinity. We provide suggestions to improve collection methods, reduce variability, and avoid confounding effects of background CORT. Background CORT was pervasive, highly variable, and may affect the physiology of larval amphibians. Collectively, this work increases our understanding of the comprehensive negative effects of wastewaters and salinity on amphibians and their physiology.

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