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Regulation of Seat-patch Water Potentials in Anurans
AuthorLemenager, Lee A.
AdvisorTracy, Richard C.
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Decades of research on water exchange in frogs have assumed that blood osmotic potential drives water uptake. However, more recent reports have suggested an intermediate control of the water potential partially separate from the osmotic potential of blood. Some reports have speculated that seat-patch may act as a compartment of water exchange between the blood and the environment. Thus, I have studied the water potential of the seat-patch and blood to evaluated their roles in water uptake in frogs. The water potentials of seat-patch and blood were measured for six anuran species, Xenopus laevis, Lithobates pipiens, L. catesbeiana, Anaxyrus boreas, Pseudacris cadaverina and P. hypochondriaca. Seat-patch water potentials were inferred from changes in body mass between frogs and different aquatic environments whose water potentials were manipulated by adjusting the osmolality of sucrose. Rates of water exchange by frogs were plotted against the osmotic potentials of environmental solutions. The x-intercepts of these graphs were taken to be the point at which water exchange is zero. The xintercept marks the point where the water potential of the frog seat-patch is equal to the water potential of the environment. Seat-patch water potentials were compared across species. The osmotic potential of blood was also measured for all species at several levels of body hydration. These water potentials of blood were compared to the seat-patch water potentials. More aquatic species had seat-patch water potentials that were less negative than those of terrestrial species, and those seat-patch water potentials were different from the water potentials of their blood. More terrestrial species had more negative seat-patch water potentials that were similar to their blood water potentials. These findings indicate a physiological mechanism in anurans to control water potential of seat-patches that has not previously been reported in the literature.