On the transfer of spatial learning between geometrically different shaped environments in the terrestrial toad, Rhinella arenarum

When trained in a rectangular arena, some research has suggested that rats are guided by local features rather than overall boundary geometry. We explored this hypothesis using the terrestrial toad, Rhinella arenarum, as a comparative contrast. In two experiments, toads were trained to find a water-reward goal location in either a featureless rectangular arena (Experiment 1) or in a rectangular arena with a removable colored feature panel covering one short wall (Experiment 2). After learning to successfully locate the water reward, probe trials were carried out by changing the shape of the arena into a kite form with two 90°-angled corners, and in the case of Experiment 2, also shifting the location of the color panel. The results of Experiment 1 indicated that the toads, in contrast to rats, relied primarily on overall shape or boundary geometry to encode the location of a goal. Under the probe conditions of the altered environmental geometry in Experiment 2, the toads seemed to preferentially choose a corner that was generally correct relative to the feature panel experienced during training. Together, the data of the current study suggest that toads and rats differ in the strategies they employ to represent spatial information available in a rectangular arena. Further, the results support the hypothesis that amphibians and mammals engage different neural mechanisms, perhaps related to different evolutionary selective pressures, for the representation of environmental geometry used for navigation.