Comparative Analyses of Spatial Cognition in Frogs Public Deposited

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  • March 19, 2019
  • Liu, Yuxiang
    • Affiliation: College of Arts and Sciences, Department of Biology
  • Efficient navigation through space is important for animal survival and reproduction. Adaptive hypothesis argues that sex and species with higher levels of cognitive challenge imposed by the environment should outperform others. To date, major efforts to understand animal spatial cognition have focused on mammals and birds. As the branch with the most primitive traits of all tetrapods, the amphibian lineage provides valuable opportunities to understand the evolution of spatial cognition in vertebrates. However, we still know relatively little about spatial cognition in amphibians. Therefore, I studied spatial cognition in this group by asking the following questions: What cognitive strategies are used in place learning? What neurogenomic mechanisms of spatial cognition exist in amphibians? Do amphibians have cognitive abilities that are comparable to mammals and birds? I studied these questions by comparing sexes and species whose natural histories differ in their spatial demands. In túngara frogs, males call from a fixed position in breeding ponds while females visit multiple males before returning to the preferred mate. Thus, females are expected to process more complicated cognitive information than males. For species comparison, Poison frogs defend territories and carry out complex parental care that relies on complex interactions with the environment, while túngara frogs do not defend territories and have no long-term parental care. Based on adaptive hypothesis, female túngara frogs and poison frogs are expected to show better performance in cognitive tasks than males and túngara frogs, respectively. I found sex differences in the use of visual cues to do place learning in túngara frogs. Females were able to use visual cues to solve the two-arm maze task while males were not (Chapter 2). On the other hand, I found túngara frogs used a cue-taxis strategy, while poison frogs used a landmark strategy to learn the same two-arm maze (Chapter 2, 3, 5). Poison frogs outperformed túngara frogs in learning acquisition and reversal training (Chapter 5). Both of sexes and species comparisons are consistent with adaptive hypotheses of spatial cognition. To understand the neurogenomic mechanisms behind the cognitive differences, I compared hippocampal transcriptomes between the two species. I found that genes related to learning and memory, neurogenesis, and synaptic plasticity were upregulated in poison frogs, while genes related to apoptosis and negative regulation of biosynthesis and metabolism were upregulated in túngara frogs. Therefore, species differences in place learning of frogs may, in part, result from differential expression of those genes in hippocampus. To determine if these species have advanced level of cognitive ability which is comparable to mammals in place learning, I trained poison frogs in a serial reversal task and a modified version of the Morris water maze. The results showed that poison frogs could use a rule-based strategy and cognitive map to learn the serial reversal task and Morris water maze respectively (Chapter 3 and 4). This is the first demonstration of a rule-based strategy and cognitive map in a non-mammalian or avian vertebrate. Given the advanced performance of poison frogs in both tasks, it is likely that poison frogs (and possibly other amphibians), have the neural architecture to generate advanced levels of spatial cognition. Future research may reveal how the complex behavior patterns encoded in mammalian and avian brains can be encoded in the neuroanatomically simpler amphibian brain.
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  • In Copyright
  • Pfennig, Karin
  • Lohmann, Kenneth
  • Sockman, Keith
  • Burmeister, Sabrina
  • Summers, Kyle
  • Doctor of Philosophy
Degree granting institution
  • University of North Carolina at Chapel Hill Graduate School
Graduation year
  • 2017

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