Chemical risk cues impact fish behavior and thermal tolerance, but effects vary with predation experience

In response to predation risk in their microhabitat, prey can use chemical risk cues to modulate their antipredator behaviors. However, prey experience with predators may alter the response to predator odors. Using two experiments and lake-side assays, we asked whether inter- and intraspecific experience with an invasive predator affected behavior and thermal tolerance of prey fishes in Lake Nabugabo, Uganda, a lake that experienced the introduction of the predatory Nile perch (Lates niloticus) in the early 1960s. In doing so, we evaluated how warming and predation risk can interact to impact prey fishes as both stressors may impact metabolism and energy use. Furthermore, we determined, for the first time, the thermal tolerance of the cyprinid Rastrineobola argentea and the characin Brycinus sadleri. We predicted that thermal tolerance would decline in the presence of predator risk and that shoaling behavior would increase with predator risk and conspecific disturbance cues. We first found that even 60 years post-invasion, three prey fishes in Lake Nabugabo failed to recognize Nile perch predator odors as risky and did not alter shoaling behaviors nor thermal tolerance. However, R. argentea, B. sadleri, and haplochromine cichlids increased shoaling behaviors in response to conspecific disturbance cues adding to the body of work demonstrating that disturbance cues can elicit antipredator behaviors in prey fishes. In contrast, in our second experiment, we compared the thermal tolerance of a population of the cichlid Pseudocrenilabrus multicolor that overlapped in the habitat with Nile perch to a population that had no habitat overlap with the predator. P. multicolor that co-occurred with Nile perch responded to Nile perch predator odors like predator odors from a native catfish predator, whereas predator-naïve cichlids failed to respond. Taken together, our experiments illustrate the importance of experience with a predator in the perception of predator odors.