Date of Graduation

8-2013

Document Type

Thesis

Degree Name

Master of Science in Biology (MS)

Degree Level

Graduate

Department

Biological Sciences

Advisor/Mentor

Gary R. Huxel

Committee Member

Steven J. Beaupre

Second Committee Member

Michelle Evans-White

Keywords

Biological sciences, Health and environmental sciences, Earth sciences, Amphibian decline, Anaxyrus americanus, Ecotoxicology, Herpetology, Lithobates catesbeianus, Pesticide, Synergistic effects

Abstract

Amphibian populations worldwide have experienced dramatic declines, and many species have already become locally, regionally, or globally extirpated with thousands more being threatened with extinction. These declines have occurred more rapidly in amphibians than any other group of vertebrates, which is especially concerning to scientists because amphibians serve as indicator species of overall environmental health. Major causes for amphibian declines are discussed in Chapter 1 and include: habitat modification and destruction, commercial over-exploitation, introduced species, environmental contaminants, global climate change, and infectious diseases.

Chapter 2 discusses the major research aspects of the thesis by examining the interactive effects of multiple stressors on two species of larval amphibians. The study investigated the individual and combined effects of a major environmental contaminant (Glyphosate, commercial Roundup ®), increased temperatures, and predatory cues on survival, growth, and development of tadpoles from two species (Lithobates catesbeianus and Anaxyrus americanus). Glyphosate reduced tadpole survival in both amphibian species and becomes more toxic to tadpoles as temperature increases. Increased temperature reduced survivorship over time in both species; however, survivorship decreased only when temperature interacted with glyphosate. Increased temperature also caused a decrease in growth in L. catesbeianus and an increase in growth and development in A. americanus. Accelerated growth and development caused by temperature may ameliorate the adverse effects of glyphosate by reducing larval period and increasing size at metamorphosis. Glyphosate caused significant anatomical shape variation in L. catebeianus, while increased temperature caused significant anatomical shape variation in A. americanus. The shape variations caused by the different stressors may lead to further developmental and behavioral abnormalities. Predatory cues had no effect on A. americanus survival, and only decreased growth and development at intermediate glyphosate concentrations and temperatures; therefore, the effects of temperature and glyphosate concentration may have been enhanced in the presence of predatory cues. The study highlighted the importance of examining the interactions between multiple stressors on amphibian declines.

Chapter 3 focuses on potential solutions for global amphibian declines. Conservation efforts such as educational outreach, effective land management and water quality regulation guidelines, captive breeding programs, and several others are discussed.

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