Date on Master's Thesis/Doctoral Dissertation

12-2018

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Biology

Degree Program

Biology, PhD

Committee Chair

Alexander, James

Committee Co-Chair (if applicable)

Eason, Perri

Committee Member

Eason, Perri

Committee Member

McGregor, Monte

Committee Member

Yanoviak, Steve

Committee Member

Steffen, Joseph

Author's Keywords

lithasia obovata; elimia semicarinata; climate change; oxygen consumption; righting behavior; pleuroceridae

Abstract

Gastropods are one of the most imperiled groups of animals in North America, yet there are major gaps in the literature pertaining to pollutants and climate change, and especially sublethal impacts. This dissertation assesses the effects of climate warming and unionized ammonia (NH3), one of the most abundant water pollutants, on the behavior and physiology of two caenogastropod snails: fine-ridged elimia (Elimia semicarinata) and Shawnee rocksnails (Lithasia obovata) (Gastropoda: Neotaenioglossa: Pleuroceridae). Righting behavior, or the movement used by snails to turn themselves right-side-up, was used as the main endpoint; delays in this behavior compromise fitness via lost feeding time and increased predation risk. NH3 experiments involved acute (24 hr) exposure to a range of concentrations, with righting time tested before and after exposure. NH3 significantly affected the change in righting time for fine-ridged elimia, with snails exposed to higher doses righting more slowly after exposure than before. Shawnee rocksnails did not experience this effect, but significantly more snails failed to right within the time limit (60 min) after exposure to 12.61 mg NH3-N/L. The concentrations that affected the behavior of these species are magnitudes greater than any reported previously for freshwater gastropods. Oxygen consumption was also tested after acute exposure to NH3 to determine if righting behavior is affected via changes to respiration, but no effects were found, suggesting that this behavior is altered by a different mechanism, at least during short-term exposure. Temperature experiments involved chronic (10-day) exposure, with righting time tested before and after. Both species failed to right at greater proportions than controls (20°C) at temperatures below their streams’ current summer highs; this effect could leave snails stranded on dry shores as water level fluctuations increase with climate change. Survival was drastically reduced at 35°C for fine-ridged elimia and 30°C for Shawnee rocksnails, 5°C less than the lower end of a common generalization of gill-breathing snail thermal tolerance. This research illustrates the importance of studying a wide range of species to determine tolerances for freshwater gastropods; conservation efforts cannot be properly informed without an understanding of the variation in sensitivities.

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