Date of Award
Master of Science (MS)
College of Science and Mathematics
Thesis Sponsor/Dissertation Chair/Project Chair
Lisa C. Hazard
The reptilian kidney can only produce isoosmotic waste. To supplement renal ion excretion and maintain ionic and osmoregulation, some reptile species rely on extrarenal salt glands that can secrete a hyperosmotic solution. Extrarenal glands among reptile taxa include the cranial gland in lizards, lacrimal gland of marine turtles, and sublingual gland of the estuarine crocodile and sea snakes. Secretion composition varies among these taxa, depending on diet, osmotic load and phylogeny. The salt glands of lizards are unique among reptiles in their ability to vary composition of the secreted fluid, secreting cations (potassium and/or sodium) and anions (chloride and/or bicarbonate). Composition of the secreted fluid depends on the ion load incurred: marine and intertidal lizards secrete primarily sodium chloride, while herbivorous lizards secrete mainly potassium chloride.
Most studies on lizard salt glands have been performed on herbivorous and marine species that have high ion loads from their diet. Many insectivorous species also possess salt glands, but their function and contribution to ion regulation have been minimally studied. Compared to marine or desert lizards, the ionic load incurred from the habitat and diet is decreased in insectivorous, arid-adapted lizards. The gland of these species, however, may still be important in maintaining ionic and osmotic balance. My goal in this study was to examine initiation of gland secretion, secretion composition and range, and the importance of the salt gland in ion regulation of an arid-adapted, insectivorous species. To evaluate these questions, I examined the response of Novoeumeces schneideri s (Scincidae) salt gland to ionic and osmotic loads.
Novoeumeces schneideri subjects were treated to different combinations of cations (sodium, potassium, and histidine control) and anions (chloride and acetate control) and salt gland secretions were examined. Lizards were injected with ion solutions (sodium chloride, potassium chloride, histidine chloride, sodium acetate, potassium acetate, histidine acetate) or controls (saline and sham injected) daily for 4 days. Secreted salt, feces and urine were collected daily and analyzed for sodium, potassium, and chloride. Daily and total cation and anion secretion rates were calculated, as well as ion secretion budgets among the salt gland, feces, and urate.
The salt glands of N. schneideri secreted only in response to chloride, regardless of the accompanying cation. Higher secretion rates were seen when histidine or potassium were accompanied with chloride. Both cations and anions were secreted in narrow ranges among all treatments, indicating limited secretion flexibility. Sodium- treated skinks showed a decreased secretion rate, suggesting a possible inhibitory role of sodium. Secretion composition contained a relatively constant mixture of potassium and sodium, regardless of the cation load.
The response of this insectivorous species differs from herbivorous and marine lizard species. Considerable plasticity in the physiology of the salt gland exists across lizard taxa, depending on physiologic needs, indicating ecologic effects on the evolutionary physiology of vertebrates.
Lechuga, Claudia, "Response of the Salt Gland of the Insectivorous Lizard Novoeumeces schneideri to Ionic and Osmotic Challenges" (2008). Theses, Dissertations and Culminating Projects. 1191.