HUNT, J.A.; FARRAR, E.S.; Iowa State University; Iowa State University: Phenotypic plasticity of the digestive system in Bufo americanus and Xenopus laevis in response to diet

Phenotypic plasticity in amphibian larvae in response to diet has been explored with respect to growth, time to metamorphosis, and development of trophic morphs, but the role of digestive system plasticity in these processes is not understood. We investigated the effects of three different diets with varying nutritional values and fiber contents on two species of tadpoles, Xenopus laevis and Bufo americanus. The three diets were high protein (Frog Brittle/Tadpole Powder, Nasco), high lipid (Zoeal Larval Shrimp Diet, Microfeast), and high fiber (crushed alfalfa). Tadpoles were fed the same weight of each diet daily to Gosner stages 31-33 from the onset of feeding. The amount was increased with tadpole growth and was in excess of daily consumption. While the Bufo survived well on all diets, Xenopus survival was very poor on high fiber. Tadpoles of both species grew less and developed slower in the high fiber group. Bufo grew larger and developed faster on the high protein, while Xenopus performed about equally well on the high protein and the high lipid diet. Intestinal lengthening was seen in the Bufo when fed high fiber, but was not seen in Xenopus. In both species, gallbladder diameters were increased in the tadpoles fed the high lipid diet, but the effects were diminished after adjusting for body weight and size. Bufo tadpoles clearly exhibited digestive system plasticity in response to the different diets, especially intestinal lengthening that correlated with increased survival on a high fiber, nutrient poor diet. Tadpoles, like Bufo americanus, that are browsers and are known to eat a wide range of foods, may also have considerable digestive system plasticity.