HUNT, J.A.; FARRAR, E.S.; Iowa State University; Iowa State University: Phenotypic plasticity of the digestive system of tadpoles in response to diet

Anuran tadpoles respond to diet by altering their growth and developmental rates. We hypothesize that digestive tract plasticity mediates these responses. We collected specimens of Bufo americanus and Rana pipiens from different habitats to determine if intestinal variation occurs in the wild. We also reared tadpoles (Bufo americanus, Rana utricularia and Xenopus laevis) on diets of either high protein (Frog Brittle/Tadpole Powder, Nasco), high lipid (Zoeal Larval Shrimp Diet, Microfeast), or high fiber (crushed alfalfa). Tadpoles were fed the same weight of each diet daily to Gosner stages 29-33 from the onset of feeding. Intestines were longer and more variable in the wild caught tadpoles. Xenopus survival was very poor on high fiber, and tadpoles of all species grew less and developed slower in the high fiber group. Intestinal lengthening was seen in the Bufo when fed high fiber. However, Rana showed intestinal lengthening in both the high lipid and high fiber groups. Intestine lengths were shortest in all species when fed the high protein diet. In Xenopus and Bufo, gallbladder diameters were increased in the tadpoles fed the high lipid diet. Tadpoles clearly show digestive system plasticity in response to diet both in the lab and probably also in the field. Intestine lengthening may promote growth in response to nutritionally poor diets but do tadpoles with longer intestines face the possible hazards of reduced streamlining, poorer swimming ability, increased predation and or reduced function of other organs occupying their small body cavities?