Fear of predators causes PTSD-like changes in brains of wild animals

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Fear of predators causes PTSD-like changes in brains of wild animals

Fear can be measured in the brain and life-threatening and terrifying life-threatening events can leave quantifiable long-term traces in the brain's neural circuits, with lasting effects on behaviour, as post-traumatic stress disorder (PTSD) very clearly shows.

A new study by Western University shows that fear-inspired predators can leave lasting traces in the neural circuits of wild animals and induce persistent fear patterns comparable to the effects observed in PTSD research.

The results of this study, led by Liana Zanette, Scott MacDougall-Shackleton and Michael Clinchy of the University of Western Ontario, were published today in Scientific Reports.

For the first time, Zanette, her students and collaborators have experimentally demonstrated that the effects of predator exposure on neural fear pathways in wildlife can persist beyond the immediate "fight or flight" reaction period and may instead remain measurable more than a week later in animals exposed in the interim to natural environmental and social conditions.

"These results have important implications for biomedical researchers, mental health clinicians and ecologists," says Dr. Zanette, a professor of biology at the University of Western Ontario's Faculty of Science and a recognized expert in ecology and neurobiology of fear. "Our results support the idea that PTSD is not unnatural and that the long-term effects of fear of predators, with likely effects on fertility and survival, are the norm in nature."

Maintaining a powerful and lasting memory of an encounter with a life-threatening predator is clearly evolutionary beneficial if it helps the individual avoid such events in the future, and a growing number of biomedical researchers have begun to propose that PTSD is the cost of inheriting an evolving primitive mechanism that gives priority to survival over quality of life.

Environmentalists recognize that predators can affect the number of prey not only by killing them, but also by frightening them. For example, Zanette et al. demonstrated in a previous study that frightened parents are less able to care for their children.

The long-term effects of fear on the brain demonstrated in this new study suggest that predator exposure could alter parental behaviour for a prolonged period of time thereafter, with greater negative effects on offspring survival than previously expected.

The team conducted the study on black-capped chickadees caught in the wild at Western's Advanced Facility for Avian Research (AFAR). For two days, individual birds were exposed to audio recordings of predator or non-predator vocalizations and then housed together in outdoor flocks for seven days, during which time they were not exposed to any other experimental evidence. After this seven-day period, persistent fear behaviour was quantified by measuring each individual's response to a tit alarm call and the long-term effects on the neural circuit of fear were assessed by measuring the levels of a genetic transcription factor in the brain (amygdala and hippocampus).