The Enduring Effects of Fear on the Brain and Behaviour in Wildlife

Abstract

Predators affect prey both through direct consumption and through non-consumptive fear effects. Predator induced fear has been shown to alter prey behaviour, where increased vigilance and reduced foraging can scale up to population and community level consequences. In this thesis, I used laboratory model studies for post-traumatic stress disorder (PTSD) as a template to study the neural mechanisms underlying the enduring behavioural response to fear in wildlife. I used audio playbacks in three manipulations in increasingly natural conditions. In all manipulations, playbacks simulated either the presence of predators or non-predator controls. Playbacks were then silenced for one week at which time I tested for enduring effects of predator induced fear in three key brain regions associated with fear processing. In Chapter 2, I quantified the enduring effects of fear on neurogenesis in laboratory housed black-capped chickadees (Poecile atricapillus). I found sex-dependent effects on hippocampal cell proliferation and suppression of immature neurons in the medial ventral arcopallium (avian homologue to the amygdala) for both sexes, consistent with an enduring memory of fear. In Chapter 3, I manipulated fear again in black-capped chickadees but this time they were living outside in semi-natural conditions. I quantified the effects of fear on foraging behaviour, activation, neurogenesis, and neuron structure. Only neuron structure demonstrated enduring effects of fear which included longer dendrites in both the hippocampus and caudolateral nidopallium (avian analogue to the prefrontal cortex) and increased dendritic branching in the caudolateral nidopallium. In Chapter 4, I manipulated fear in free-living meadow voles (Microtus pennsylvanicus). I report enduring, sex dependent, effects of fear on neural activation, neurogenesis, and apoptosis, and enduring effects of fear on neuron structure in both sexes. Enduring effects on neurobiology were accompanied by a behavioural shift in nocturnal activity whereby voles who heard predators one week earlier were caught later in the night. Overall, my thesis demonstrates that wildlife show enduring, PTSD-like effects on neurobiology in response to predator-induced fear and that these effects are often sex dependent. Demonstrating PTSD-like effects on the brains of wild animals suggests that predator-induced fear may have adaptive value for surviving future predator encounters.