Abstract
Evidence suggests that brain serotonin (5-HT) is one of the central mediators of different types of animal personality. We tested this assumption in field crickets Gryllus integer using a selective serotonin reuptake inhibitor (SSRI). Crickets were selected for slow and rapid development and tested for their coping styles under non-stressful conditions (time spent exploring a novel object). Resting metabolic rate, maximum metabolic rate and latency to resume activity were measured under stressful conditions (stress reactivity). Measurements were taken (i) before and (ii) during the SSRI treatment. Before the SSRI treatment, a strong negative correlation was observed between coping style and stress reactivity, which suggests the existence of a behavioral syndrome. After the SSRI treatment, the syndrome was no longer evident. The results of this study show that 5-HT may be involved in regulating behavior not only along a stress reactivity gradient but also along a coping styles axis. The relationship between personality and the strength and direction of 5-HT treatment on observed behaviors indicates trait-like individual differences in 5-HT signaling. Overall, these findings do not support recent ideas arising from the pace-of-life syndrome (POLS) hypothesis, which predict higher exploration and metabolic rates in rapidly developing bold animals.
Highlights
Phenotypic differences in trait expression are a prerequisite for evolution through natural selection
The pace-of-life syndrome (POLS) hypothesis, rooted in the classic concept of r- and K-selection, is relevant in this context[14,15,16], as it suggests that life history traits such as age at maturity and growth rate are likely coupled with individually consistent behaviors and immune responses
According to the two-tier model of animal personality proposed by Steimer et al.[20], coping styles reflect the quality of the response to a stressor, while stress reactivity reflects the quantity of the response expressed
Summary
Phenotypic differences in trait expression are a prerequisite for evolution through natural selection. Most of the traits of an organism vary around a mean value, research on human and animal behavior has revealed between-individual clusters in behavioral responses, often attributed to different personality axes that are called personality types, behavioral predispositions, temperaments or coping styles. According to the two-tier model of animal personality proposed by Steimer et al.[20], coping styles reflect the quality of the response to a stressor, while stress reactivity reflects the quantity of the response expressed In this model, bold individuals are those with a strong tendency to act (proactivity) combined with low stress reactivity. The reactively coping animal tends to rely more on a detailed appraisal of their current environment because they react to immediate environmental stimuli and tend to explore any changes in their environment
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