Determinants of the water seeking response in a T-maze in the fire-bellied toad Bombina orientalis

Abstract

To maintain water balance, terrestrial amphibians are motivated to seek water when dehydrated and to avoid hypertonic solutions that promote water loss to the environment. Thus, dehydration and hypertonic solutions both act to promote positive water balance through opposite appetitive and aversive mechanisms. In one experiment, we tested if appetitive and aversive stimuli interact to facilitate learning of the location of a water source in the fire-bellied toad Bombina orientalis. Dehydrated and hydrated toads were placed in a T-maze with accessible distilled water in one arm and hypertonic saline or inaccessible water in the other arm. Maze performance was assessed by measuring time to find the water source and correct first choices over 6 consecutive days of training. Results showed reduced time to find water in dehydrated toads but no reliable improvement in correct first choices that would indicate spatial learning. Hypertonic saline inhibited maze exploration but otherwise had no effect on performance. Because we expected spatial learning for water based on previous work in this species (Brattstrom, 1990 J Herpetol 24:44−47), we conducted a second experiment with longer training, again including dehydrated and hydrated toads. Maze training for four weeks with four weekly trials revealed a rapid reduction in time to find water in dehydrated toads followed later by an improvement in correct first choices suggestive of spatial learning. Additionally, changing the motivational status of toads after the four-week training period showed no evidence that hydrated toads had learned location of the water source during training. Our results suggest that both motivational and learning effects ameliorated water seeking behaviour in this terrestrial amphibian, but that motivation acted much faster than learning. Additionally, toads that experienced no reinforcement during training showed no latent learning effect.