Abstract
The occurrence of emotions in non-human animals has been the focus of debate over the years. Recently, an interest in expanding this debate to non-tetrapod vertebrates and to invertebrates has emerged. Within vertebrates, the study of emotion in teleosts is particularly interesting since they represent a divergent evolutionary radiation from that of tetrapods, and thus they provide an insight into the evolution of the biological mechanisms of emotion. We report that Sea Bream exposed to stimuli that vary according to valence (positive, negative) and salience (predictable, unpredictable) exhibit different behavioural, physiological and neuromolecular states. Since according to the dimensional theory of emotion valence and salience define a two-dimensional affective space, our data can be interpreted as evidence for the occurrence of distinctive affective states in fish corresponding to each the four quadrants of the core affective space. Moreover, the fact that the same stimuli presented in a predictable vs. unpredictable way elicited different behavioural, physiological and neuromolecular states, suggests that stimulus appraisal by the individual, rather than an intrinsic characteristic of the stimulus, has triggered the observed responses. Therefore, our data supports the occurrence of emotion-like states in fish that are regulated by the individual’s perception of environmental stimuli.
Highlights
The interest in the study of emotion in non-human animals dates back to the publication of Darwin’s monograph “The Expression of Emotions in Man and Animals”[1]
The behaviour displayed by fish during the test trial was specific of each treatment: expression of social interactions occurred mostly among the individuals of the appetitive treatments, and these were more frequent in predictable appetitive (PRDapp) than UnPRDapp (F(1, 44) = 12.21; p = 0.001; see Fig. 1a for planned comparisons); on the other hand, escape attempts were expressed mainly among individuals of the aversive treatments(i.e. total of 7 events in 48 fish), and these were more frequent in predictable aversive (PRDavr) than in UnPRDavr (valence x predictability: F(1, 85) = 25.61; p < 0.001; see Fig. 1b for planned comparisons)
In this study we have shown that Sea Bream exposed to stimuli that vary according to valence and salience exhibit different behavioural, physiological and neuromolecular states that are specific to each combination of valence and salience
Summary
The interest in the study of emotion in non-human animals dates back to the publication of Darwin’s monograph “The Expression of Emotions in Man and Animals”[1]. Other dimensions of emotion, namely the expression of emotion-specific behaviour and accompanying physiological responses, have been documented in many species and a consensus has emerged that animals should express organismic states that index occurrences of value in the environment, regardless of whether these states are consciously experienced[2,3,4,5] These organismic states would be triggered by the value, in terms of potential impact in Darwinian fitness, that an animal ascribes to a stimulus and they would instantiate the ability to respond adaptively to environmental threats (e.g. presence of predators; presence of competitors for resources, such as shelters or territories) and opportunities (e.g. mating partners; food availability; possibility of ascending in social hierarchy). Behavioural states were characterized by the expression of observed behavioural patterns, namely, social interactions and escape attempts
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