Prey responses to disturbance cues: Effects of familiarity, kinship, and past experience with risk

Prey can acquire information about predators by eavesdropping on conspecific cues, but these cues are not always reliable. In aquatic systems, disturbance cues are pulses of urea or ammonia that are often released by prey while fleeing a predator; nearby individuals typically display antipredator responses after detecting these cues. Despite the importance of disturbance cues to aquatic prey survival, they remain largely understudied in terms of their function and evolution. Here, I sought to test whether disturbance cues might function as an antipredator signal. Using a series of experiments, I assessed how familiarity and relatedness with individuals releasing the cues affects the antipredator response of the receiver, and whether background risk levels for the cue releaser and receiver play a role in the response exhibited by the receiver. If prey rely more on disturbance cues from familiar, related, or high predation risk background conspecifics, then I expect to see a heightened fright response to these cues. To test this, I raised wood frog (Lithobates sylvaticus) egg clutches and obtained disturbance cues from groups of tadpoles by simulating a predator chase. Counter to expectation, tadpoles exposed to disturbance cues from unfamiliar individuals displayed a fright response, whereas disturbance cues from familiar individuals were ignored, possibly because these cues became unreliable after being detected repeatedly in the absence of a true threat. Tadpoles responded similarly to the disturbance cues of related and unrelated individuals, suggesting that related individuals did not provide more reliable information. When manipulating background predation risk, high-risk receivers but not low-risk receivers responded to disturbance cues from low-risk donors, suggesting a lower response threshold in high risk prey. Disturbance cues from high-risk donors also elicited more of a fright response in both high- and low-risk receivers. This suggests that high risk prey release more, or more potent disturbance cues. Taken together, these experiments provide strong evidence that tadpoles detect variation in disturbance cues and may be capable of modulating their disturbance cues as antipredator signals. These findings are of important consideration for conservationists studying how Allee effects manifest in threatened aquatic species such as anuran tadpoles