The curious case of the cane toad (Rhinella marina): An assessment of exploratory behavior and foraging success of an invasive vertebrate in a novel environment



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An individual’s ability to modify its behavior as a result of experience is a key component of successful survival in a changing environment. This ability has been studied in many taxa including vertebrates (e.g. mammals, birds and fish) and invertebrates (e.g. insects and cephalopods), however little conclusive evidence exists for learning in anuran species. Much of the research previously done in this area was constrained by unsuccessful attempts to develop an experimental paradigm that provided evidence in support of learning in these taxa. The research outlined in this thesis synthesizes laboratory and field designs to provide a new approach to studying learning abilities in anurans, pertaining to exploration and foraging behavior on an individual scale. The cane toad, Rhinella marina, is an ideal study species to determine the role of learning in anurans. Its well-known invasive capabilities and colonization of new environments suggest that cane toads are experts at modifying their behavior based on changes in the environment. By studying how exploratory behavior in a novel environment is modulated by experience, we can make inferences about the spatial learning abilities of this species. To examine the potential role of learning in invasive potential we conducted similar studies with cane toads from populations in both the native and invasive ranges. To further provide evidence for learning in anurans we asked the same questions about a congeneric species of toad from the native range with differing life history strategies, the leaf litter toad (Rhinella alata). For cane toads in both the native and invasive ranges, individuals were repeatedly tested in an exploratory arena in one of two treatments, with or without food present. After initial training in the arena toads were tested to determine if movement and behavioral strategies changed over time, as experience with the arena increased. Toads were given five trials each, with a sixth trial to tease apart the use of associative learning or spatial cues for foraging behavior. The smaller leaf litter toads were tested in an arena scaled to size based on their locomotor ability, and were tested with food in the arena for five total trials. Cane toads from both the native and invasive ranges showed a decrease in movement and exploration over time, regardless of treatment group. Individuals in the experimental treatment (food in bowls) ate more mealworms over time while still decreasing overall movement. Leaf litter toads did not show any significant trends in either foraging or exploratory behavior while in the arena, though a large proportion of the individuals successfully learned to eat the novel food item used for feeding before and during trials. Our results indicate that cane toad behavior is modulated by experience with a novel environment and by the presence of food. This study ultimately emphasizes the role of learning in foraging in cane toads, a characteristic that may have facilitated their success as invaders.