Evidence for incipient alarm signalling in fish

In Focus: Bairos-Novak, K.R., Ferrari, M.C.O., & Chivers, D.P. (2019). A novel alarm signal in aquatic prey: Familiar minnows coordinate group defences against predators through chemical disturbance cues. Journal of Animal Ecology, 88, 1281-1290, https://doi.org/10.1111/1365-2656.12986. Chemicals released during predation have long been studied as cues to nearby prey that predators are active in the vicinity. Until now, these chemicals have been labelled as cues because there was no compelling evidence for the necessary components of a communication system, namely (a) voluntary control of release of information, (b) capacity for graded responses and (c) the presence of specialized structures for the production and release of the signal. New findings by Bairos-Novak, Ferrari, and Chivers (2019) show that fathead minnows alter the potency of disturbance "cues" when in the presence of other fathead minnows compared to when they are alone and produce either more or different disturbance "cues" when in the presence of familiar conspecifics compared to when they are in the presence of unfamiliar conspecifics. The behavioural response to these cues is shoaling, which would confer fitness benefits to the sender, thereby qualifying as a signal rather than a cue. This is a significant advancement in the field of chemical ecology of aquatic organisms because disturbance "cues" by fathead minnows bear two of the three hallmarks of an incipient disturbance "signal".