Generalization of predators and nonpredators by juvenile rainbow trout: learning what is and is not a threat

Abstract

Learned recognition of novel predators allows prey to respond to ecologically relevant 27 threats. Prey could minimize the costs associated with learning the identity of both 28 predators and nonpredators by making educated guesses on the identity of a novel species 29 based on their similarities with known predators and nonpredators, a process known as 30 generalization. Here, we tested whether juvenile rainbow trout, Oncorhynchus mykiss, 31have the ability to generalize information from a known predator (experiment 1) or a 32 known harmless species (experiment 2) to closely related but novel species. In 33 experiment 1, we taught juvenile trout to recognize a predatory pumpkinseed sunfish, 34Lepomis gibbosus, by pairing pumpkinseed odour with conspecific alarm cues or a 35 distilled water control. We then tested the trout for a response to pumpkinseeds and to 36 novel longear sunfish, Lepomis megalotis (same genus as pumpkinseed), rock bass, 37 Ambloplites rupestris (same family as pumpkinseed) or yellow perch, Perca flavenscens 38 (different family). Trout showed strong learned recognition of pumpkinseed and longear 39 sunfish odour and a weak learned response to rock bass odour but no recognition of 40 yellow perch. In experiment 2, we used latent inhibition to teach juvenile trout that 41 pumpkinseeds were harmless. During subsequent predator learning trials, trout did not 42 learn to recognize pumpkinseed or longear sunfish odour as potential threats, but they did 43 learn that rock bass and yellow perch were threatening. Taken together, these results 44 demonstrate that juvenile rainbow trout can generalize learned recognition of both 45 predator and nonpredator odours based on the phylogenetic relatedness of predators.

Learning about Danger: Chemical Alarm Cues and Threat‐Sensitive Assessment of Predation Risk by Fishes

“…A series of elegant studies with mammals (Griffin et al 2001;Stankowich & Coss 2007), amphibians (Ferrari et al 2009b) and fishes (Ferrari et al 2007(Ferrari et al , 2010bBrown et al 2011a) have shown that prey conditioned to a reference predator can exhibit learned responses to chemical and visual cues of predators with which the prey have no experience. Moreover, predators that are more distantly related to the reference predator are not recognised.…”

“…There was no inhibition of learning of rock bass or yellow perch odours. Modified from Brown et al (2011a).…”

“…Brown et al (2011a) used this latent inhibition mechanism to test the hypothesis that juvenile rainbow trout can generalise the recognition of both predator and non-predator cues. In their first experiment, juvenile trout were conditioned to recognise pumpkinseed odour as a reference predator and then tested for the recognition of pumpkinseed, longear sunfish, rock bass or yellow perch odours.…”

Phenotypically plastic neophobia: a response to variable predation risk

“…However, recent evidence suggests that predator recognition is much more sophisticated. For instance, prey species can display an anti-predator response towards a novel predator upon their first encounter if the predator species is related to a species already recognized as dangerous by the prey [26,43]. In amphibians, occurrences of the so-called 'innate' predator recognition in wild populations sympatric with predators (e.g.…”

Diet cues alter the development of predator recognition templates in tadpoles

“…A look at the predator recognition literature suggests that not all information available from predators is equal and that different species focus on certain cues whilst ignoring others. For visual features, prey appear to preferentially focus on those that specifically relate to predatory functions, such as the morphology of eyes and their position on the head (Karplus et al 1982;Beránková et al 2014), size and shape of the mouth (Karplus et al 1982), size/shape/silhouette of the body (Engstrom-Ost and Lehtiniemi 2004;Stankowich and Coss 2007;Brown et al 2011) and posture/orientation (Helfman 1989;Cooper 1998;Schluessel et al 2014). Experimentally modifying these features can significantly impact antipredator responses of prey, whilst modifying non-functional features has little or no effect (Karplus et al 1982;Beránková et al 2014).…”