Abstract
Animals display fear-like behaviours before escaping from predators. This response triggers both behavioural and physiological changes in multiple body systems, allowing animals to escape danger and ensure survival. Fear-like behaviour is modulated by the serotonergic system in the brain of vertebrates, which shapes social behaviour and cooperative behaviours. Using fluoxetine (FLX), a common pharmaceutical that alters the levels of serotonin in the brain, we aimed to clarify whether the same is true in solitary animals like green turtles Chelonia mydas. Green turtles exhibit individual differences in their response to risk. If fear-related behaviours are regulated by the serotonin system in turtles, the fear-like responses of individuals injected with FLX could change. We therefore assessed the effect of FLX injection on the behavioural responses to a fear stimulus in 9 wild juvenile green turtles in an aquarium setting. We inserted a hand net as a stimulus into the aquarium (within a designated inspection zone) to elicit a fear-like behaviour and measured the time that turtles spent in this zone. All turtles exhibited fear-like behaviour and fled from the stimulus prior to any injection treatment. Turtles with control injection (no FLX) also fled and avoided the inspection zone with the fear stimulus. FLX injection appeared to reduce the turtles’ fear of the stimulus: The total time turtles injected with FLX spent in the inspection zone was significantly longer than for turtles that received a control medium injection. Control turtles fled from the stimulus and were initially vigilant and avoided the area with the stimulus, but then moved throughout the aquarium, including the inspection zone. These data suggest that fear-like behaviour is modulated by the serotonin-mediated nerve system in juvenile green turtles.
Highlights
Animals show fear-like behaviours to avoid or escape from predators
Juvenile green sea turtles fled from the fear stimulus, and the stimulus elicited turtle responses that indicated fear-like behaviour
The turtles injected with FLX remained in the inspection zone for a longer time than those injected with the control injection
Summary
Animals show fear-like behaviours to avoid or escape from predators. Avoiding predation is a preeminent selective force in nature because failing to do so immediately reduces the individual’s future fitness (Werner & Peacor 2003). When the guppy treated with fluoxetine (FLX), a commonly prescribed antidepressant in the family of selective serotonin reuptake inhibitors that alters the levels of serotonin in the brain, was exposed to the stimulus of predator animation, it was found to spend more time near the predator image and freezing and less time avoiding the predator. This observation suggests the role of serotonin in cooperative behaviours (Pimentel et al 2019)
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