Date of Award

5-2011

Document Type

Thesis

Degree Name

Master of Science (MS)

College/School

College of Science and Mathematics

Department/Program

Biology

Thesis Sponsor/Dissertation Chair/Project Chair

Lisa C. Hazard

Committee Member

Meiyin S. Wu

Committee Member

Sandra Adams

Abstract

Amphibian decline has been a global phenomenon in recent decades due in part to negative human effects on the environment. Sensitivity of amphibians to environmental degradation makes them good indicators of environmental change, attesting to the importance of amphibian inventory and population monitorings De-icing salts, such as sodium chloride, are applied to roads during the winter months and may accumulate in aquatic and terrestrial habitats. The exposure of amphibians to high salt concentrations can impair their physiological functioning due to their highly permeable skin. The purpose of this investigation is to examine the behavioral tolerance threshold for road salt (NaCl) for the green frog (Rana clamitans) and wood frog (Rana sylvatica). These species were chosen based on levels of terrestriality; green frogs spend most of their time in or near water, while wood frogs breed in vernal pools and spend the rest of the year in moist woodlands. In 10-minute trials, the frogs were allowed to choose between a NaCl solution ranging from 0 to 0.5 M concentration and a control solution (aged tap water, 0 M) to examine their behavioral tolerance to saltwater; mass change due to osmotic water flux was also measured. Despite the close relatedness of the two species, evidence shows that their salinity threshold varies. Green frogs showed an aversion to increasing NaCl concentrations. However, the wood frogs showed no aversion during the 10-minute trials and little to no aversion during subsequent 20 and 30-minute trials. Differences between these species may be due to higher tolerance of dehydration in wood frogs due to their more terrestrial nature or more specifically due to their tolerance of increased internal osmolarity as a part of their mechanism for tolerating freezing conditions.

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