Exploring learning and sound conditioning in American toads (Anaxyrus americanus)

Tucker Hall Room 118 & Webinar (email BallewR@missouri.edu for webinar link)

The efforts to better understand the minds of animals have been flourishing, with methodological breakthroughs and a remarkable increase in the number of publications dealing with a wide variety of non-model species. The growing interest in species that are distantly related to humans in the field of comparative physiology and cognition was confirmed with the general reviewed performed in this dissertation. Yet, the progress is unbalanced among the ectothermic vertebrates (fish, reptiles, and amphibians), with almost no research on amphibians. Many animals remain unstudied, even though they may possess unique and powerful adaptations to respond to environmental stimuli that can be useful for learning and cognition research.  Inspired by the efforts to increase species representation in studies of learning and cognition, this dissertation also explored two methods of spatial learning to train American toads to respond to tone burst cues in order to find the reward. As frogs and toads have been able to acquire maze task associated to visual cues and mating calls, I predicted that a protocol based on these previously successful methods could be reliable in testing toads to associate and discriminate tone bursts of different frequencies (HZ). None of the methods were effective in demonstrate learning abilities in American toads, but the results pointed to important challenges to calibrate methods for future studies. Aspects to consider such as sex effects on side bias and can be used to reflect behavioral plasticity as a metric for the process of learning, such as time latency (longer it takes a toad to succeed, the more likely they will be successful) and the behavior displayed during the task as an indication of behavioral flexibility for decision making. Besides these aspects of the procedure, there are physiological and evolutionary aspects that might make toads unable to interact with non-mating sounds. These aspects and the level of hearing constraints that can affect learning assessment in toads are critical to answer broad questions on anuran auditory role beyond mating purposes.  


  • Dr. H. Carl Gerhardt, Primary mentor
  • Dr. Manuel Leal
  • Dr. Johannes Schul
  • Dr. Kevin Middleton
Speaker Information

Deise Cruz Santos
Ph.D. Candidate - Gerhardt Lab
Division of Biological Sciences
University of Missouri