Development of Conditioned Taste Aversion in Amphibians

Kyla D’Angelo, Iona College ’10 and Prof. Erica Crespi

The aim of this study was to see whether an animal could learn to avoid negative environmental stimuli. The environmental stimulus used in this experiment was the ingestion of a novel food, which caused a visceral illness. The pairing of the novel food with a visceral illness should signal to the animal that the food is toxic. This type of learning, conditioned taste aversion, allows the animal to avoid this toxic flavor, therefore increasing its chances of survival. This study focuses on whether later stage Wood Frog (Rana sylvatica) tadpoles could develop CTA and retain the memory of CTA through metamorphosis. There have been very few studies investigating this phenomenon in amphibians and none to date that have looked specifically at later stage tadpoles. However, it has been shown that later stage Manduca sexta caterpillars retained conditioned odor aversion through metamorphosis (Blackiston, Casey, Weiss, 2008). Catepillars are similar to tadpoles because they both have to go through a larval stage, in which their entire digestive system is radically changed. A study by Mikulka, Vauhgan, and Hughes (1981) showed that adult toads were able to develop conditioned taste aversion and would avoid noxious food objects such as crickets or mealworms that were treated with hydrochloric acid. If both the tadpole and the frog can separately develop CTA, the later stage tadpoles should be able to develop CTA and retain the memory of CTA through metamorphosis. CTA will be developed by injecting the appropriate group with LiCl (1.56mg/50ml H2O) an hour after eating the “aversive” flavor. The control for the LiCl injections will be saline (PBS-1x) injections that are given one hour after eating the “novel” flavor. One week after the conditioning schedule is completed, each individual tadpole will be given 3 different preference tests over three days. Results have shown that the LiCl injections were successful in inducing a visceral illness in the tadpoles. The raspberry aversion group developed a conditioned taste aversion for raspberry flavoring alone, while it appears that the vanilla aversion group developed a conditioned taste aversion for both vanilla and raspberry flavoring. Future studies aim to identify the brain regions that are stimulated when tadpoles are exposed to a novel flavor by assaying for BrdU and determining whether stress response is associated with the conditioned taste aversion by assating for corticosterone.