Date of Award

Fall 12-2016

Degree Type

Masters Thesis

Degree Name

Master of Science (MS)

Department

Ocean Science and Technology

Committee Chair

Dr. Darrell J. Grimes

Committee Chair Department

Ocean Science and Technology

Committee Member 2

Dr. Andrew N. Evans

Committee Member 2 Department

Ocean Science and Technology

Committee Member 3

Dr. Natalie D. Mylniczenko

Abstract

The elasmobranch osmoregulatory strategy is predicated on the accumulation of nitrogenous compounds, primarily urea and trimethylamine n¬-oxide (TMAO). Despite the abundance of these plasma osmolytes, it is notable that elasmobranchs appear to lack urease and TMA oxidase (Tmase), enzymes that scavenge urea-nitrogen and synthesize TMAO, respectively. However, urease and Tmase are found in many species of bacteria. Therefore, I hypothesized that intestinal bacteria are responsible for urease and Tmase activity in elasmobranchs. Absent dietary nitrogen sources, I evaluated the effects of reduced intestinal microbiota on osmoregulation in Atlantic stingray (Dasyatis sabina) in vivo. D. sabina were given daily broad-spectrum antibiotics per os and monitored for weight loss, plasma osmolality, amine metabolites, urea, and TMAO. qRT-PCR was used to determine the efficacy of antibiotics at reducing the intestinal microbial community and to quantify the hepatic expression of carbomoyl phosphate synthetase III (CPS III), the rate-limiting enzyme in urea production. Though antibiotics significantly reduced the bacterial community in the D. sabina gut, there was no significant change in plasma osmolality, urea, or TMAO. However, amine metabolites changed significantly within control and antibiotic groups including benzoic acid, arginine, creatinine and L-citrulline. Also observed was significant down-regulation of CPS III expression, suggesting that urea production decreased in antibiotic-treated individuals. My findings suggest that elasmobranch osmoregulation is robust to microbiome perturbation and supports the hypothesis that plasma osmolytes are highly conserved in elasmobranchs. This is the first study to test the efficacy and subsequent effect of antibiotics on the elasmobranch intestinal microbiome and osmoregulation.

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