Date of Award:

8-2013

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Biology

Committee Chair(s)

Edmund D. Brodie Jr.

Committee

Edmund D. Brodie Jr.

Committee

Susannah S. French

Committee

Michael E. Pfrender

Committee

Peter K. Ducey

Committee

Lee Rickords

Abstract

Tetrodotoxin (TTX) is a potent neurotoxin found in a variety of species. This toxin has long been of concern to human health as it is found in puffer fish, which are a delicacy in Japan. Since the distribution of this toxin is so great, there are many questions regarding the evolution and ecology of organisms that have TTX. My research has focused on further investigating three topics with this research: production, predation, and identification of novel TTX bearing taxa. In order to perform this research I first refined a Competitive Inhibition Enzymatic Immunoassay methodology to quantify levels of TTX in tissue.

Production: There is not a consensus among the scientific community as to how TTX is produced. Given that it is found in such a wide variety of species, it has been thought that perhaps bacteria and then bioaccumulated through the food chain to larger organisms. However, there is little support for this in newts (Taricha granulosa). I investigated this question by looking at TTX levels in newt eggs over time in the lab. It is thought that if they acquire TTX from somewhere else, levels will drop in the lab because they have non-TTX bearing diets. However, if TTX is produced by the newts TTX levels should remain relatively constant. We found that after the initial capture, TTX levels declined. However, they remained constant in the three following years. I believe that the initial decline was due to the shortened breeding period in the lab, and that this study is further evidence for TTX production in these newts.

Predation: The high levels of TTX found in newts has resulted in few predators. I observed river otters feeding on these newts in a high elevation lake in Oregon. I found that this population has low levels of TTX, which enabled otters to eat them. Further, I found that high elevation populations in Oregon tend to have lower TTX levels than do low elevation populations in general.

Novel species: Tetrodotoxin has never been identified in a terrestrial invertebrate. I identified TTX in two species of terrestrial flatworms (Bipalium adventitium and B. kewense). Further, I found that TTX likely is utilized by these species in order to protect them from predation and to subdue larger prey items

These studies have provided further evidence for the production of TTX as well as the biotic and abiotic interactions surrounding organisms that have TTX. This will help us understand the evolution of this toxin.

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