Abstract
Social stressors typically elicit two distinct behavioural responses in vertebrates: an active response (i.e., “fight or flight”) or behavioural inhibition (i.e., freezing). Here, we report an interesting exception to this dichotomy in a Caribbean cleaner fish, which interacts with a wide variety of reef fish clients, including predatory species. Cleaning gobies appraise predatory clients as potential threat and become stressed in their presence, as evidenced by their higher cortisol levels when exposed to predatory rather than to non-predatory clients. Nevertheless, cleaning gobies neither flee nor freeze in response to dangerous clients but instead approach predators faster (both in captivity and in the wild), and interact longer with these clients than with non-predatory clients (in the wild). We hypothesise that cleaners interrupt the potentially harmful physiological consequences elicited by predatory clients by becoming increasingly proactive and by reducing the time elapsed between client approach and the start of the interaction process. The activation of a stress response may therefore also be responsible for the longer cleaning service provided by these cleaners to predatory clients in the wild. Future experimental studies may reveal similar patterns in other social vertebrate species when, for instance, individuals approach an opponent for reconciliation after a conflict.
Highlights
Animals are continuously faced with a wide range of environmental and social pressures, and are forced to make decisions in order to survive [1]
While it is clear that predation risk can induce significant changes to a prey’s behaviour and even to population dynamics, less is known about the relevant causal mechanisms that are directly responsible for these alterations, when predation risk affects prey foraging decisions [6,7]
The effects of predation risk seem to play an important role in mediating changes in foraging behaviour of cleaning gobies
Summary
Animals are continuously faced with a wide range of environmental and social pressures, and are forced to make decisions in order to survive [1]. Predators are notorious inducers of stress responses [3] These responses usually involve a suite of hormones known to mediate stress responses [8]. These hormones belong to two endocrine systems: the catecholamine response and the glucocorticoid response [9]). Glucocorticoids can cross the blood-brain barrier and access receptors in several brain regions This makes their potential role in stress response important because in order to affect behaviour, the mediation of stress must affect the brain [8]. When referring to social stress in vertebrates, this physiological cascade is usually described as being able to elicit one of two alternative behavioural responses: a proactive response (active coping, or ‘fight-flight’) or a reactive response (passive coping, or ‘conservation-withdrawal’) [10]. The threshold at which the shift occurs from a more passive to an active response to a certain stimulus should be determined by individual cognitive appraisal of the stimulus [11]
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