Innate chemical, but not visual, threat cues have been co-opted as unconditioned stimulus for social fear learning in zebrafish.

Julia S Pinho,Rui F Oliveira,Marisa Castilho,Joao S Sollari

doi:10.1111/gbb.12688

Abstract

Animals can use social information to detect threat in the environment. In particular, social learning allows animals to learn about dangers without incurring in the costs of trial-and-error learning. In zebrafish, both chemical and visual social cues elicit an innate alarm response, which consists of erratic movement followed by freezing behavior. Injured zebrafish release an alarm substance from their skin that elicits the alarm response. Similarly, the sight of conspecifics displaying the alarm response can also elicit the expression of this response in observers. In this study, we investigated if these social cues of danger can also be used by zebrafish as unconditioned stimulus (US) in learning. We found that only the chemical cue was effective in the social fear conditioning. We suggest that this differential efficacy of social cues results from the fact that the alarm cue is a more reliable indicator of threat, than the sight of an alarmed conspecific. Therefore, although multiple social cues may elicit innate responses not all have been evolutionarily co-opted to act as US in associative learning. Furthermore, the use of the expression of the immediate early genes as markers of neuronal activity showed that chemical social fear conditioning is paralleled by a differential activation of the olfactory bulbs and by a different pattern of functional connectivity across brain regions involved in olfactory processing.

Highlights

A key component of Darwinian fitness is the ability of animals to detect and respond to the presence of danger in the environment, namely predators
Our results demonstrate for the first time, that zebrafish learn a conditioned fear response using alarm substance but not the sight of an alarmed conspecific as a unconditioned stimulus (US)
Zebrafish innately respond both to chemical and visual alarm cues, only chemical cues are efficient as an US in fear conditioning

Summary

| INTRODUCTION

A key component of Darwinian fitness is the ability of animals to detect and respond to the presence of danger in the environment, namely predators. The ubiquity of social fear learning across different taxa and using different sensory modalities reflects its adaptive importance, since it allows individuals to learn about threat without using trial-and-error learning in an ecological domain, where the cost of misses would be very high, most probably death.[19]. Zebrafish uses both chemical and visual social threat cues to assess the presence of danger in the environment, and responds to these with an innate alarm response, which consists of erratic movement followed by freezing behavior. Here we used the expression of these four different IEGs in order to capture possible different aspects of memory formation during social fear learning in zebrafish

| MATERIALS AND METHODS

Findings

| DISCUSSION