Date of Award

Spring 2011

Document Type


Degree Name

Master of Science (MS)


Biological Sciences



Committee Director

Alan H. Savitzky

Committee Member

Deborah A. Hutchinson

Committee Member

David T. Gauthier

Call Number for Print

Special Collections LD4331.B46 M65 2011


Toads are chemically defended by bufadienolides, a class of cardiotonic steroids lethal to most predators, including many snakes. Bufadienolides bind to Na+K +-ATPase, inhibiting their ability to transport ions. In cardiocytes, this inhibition cause arrhythmia and severely increased contraction strength, which, if prolonged, lead to death. However, several snakes are resistant to bufadienolides and consume toads with no ill effects. Adrenal glands produce hormones that are important for the maintenance of Na+K +ATPase, and may therefore play an important role in countering the negative effects of bufadienolides. Indeed, the toad-eating specialist Heterodon platirhinos has been known to possess enlarged, and sexually dimorphic, adrenal glands. I hypothesized that toadeating snakes have modified adrenal glands that play a role in the snakes' resistance to bufadienolides and that sexual dimorphism in adrenal gland size is a general characteristic of bufophagous snakes. I used phylogenetically independent taxa to investigate adrenal morphology in bufophagous and non-bufophagous species. Icompared adrenal mass among species and found that the allometric relationship between adrenal mass and body size is significantly different in bufophagous and non-bufophagous snakes, and that these differences also exist between sex in bufophagous species. One bufophagous species, Natrix natrix,fell out of the pattern seen in the others, having adrenal glands more similar to nonbufophagous species. In addition to the morphological comparisons, I compared tissue proportions in histological sections of the adrenal glands but found no significant differences there.


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