The role of early life history in learning and retention of predator recognition by fish and amphibians

Abstract

Predation risk is a major driver of evolution and ecology of animals. Predator avoidance is essential because failing to evade threats will result in injury or death. However, avoiding predators is costly because it means missing out on foraging and mating opportunities. To maximize opportunity, organisms must be able to perceive and assess threat levels, allowing them to avoid reducing activity when risk is minimal. Many aquatic organisms use injury-released “alarm” cues from conspecifics to detect a predation threat. They may learn to recognize predators from simultaneous exposures to alarm cues and a novel predator odour. Any other information that they can incorporate as they are learning may improve the accuracy with which they can predict the degree of threat in subsequent exposures. In this thesis, I explore embryonic and early learning of predator recognition by aquatic organisms. Using paired exposure to alarm cues and novel predator odours, I show that embryonic fish are not only able to learn to recognize predators, but can also do so in a threat-sensitive manner and from cues of closely-related heterospecific fish. I also demonstrate that the effect of a difference in age between the alarm cue producer and receiver varies between species and is situation-dependent. Specifically, newly-hatched rainbow trout respond equally to alarm cues from newly-hatched and six-month-old individuals at various concentrations. In contrast, although the scientific record shows that embryonic minnows hatch early in response to embryonic alarm cues, I found that they do not modify their hatching time in response to adult alarm cues. I also use learning exposures of paired alarm cues and predator odour at different early life stages to demonstrate that ontogeny has significant impacts on fish and tadpoles’ retention of learned predator information, whereby embryonic learners forget more slowly than slightly older larval conspecifics. I propose that embryonic learners may have increased cognitive plasticity as a result of a sensitive period in their development.