The fear predators inspire in their prey can leave long-lasting traces in the brains of wild animals, comparable to effects seen in humans dealing with post-traumatic stress disorder (PTSD), according to a Western-led study. The findings further demonstrate PTSD as a natural reaction of the brain to stressful situations.
Led by Biology professor Liana Zanette, Psychology professor Scott MacDougall-Shackleton and Biology professor Michael Clinchy, the study, Predator-induced fear causes PTSD-like changes in the brains and behaviour of wild animals, was published today in Scientific Reports–Nature.
In this study, researchers demonstrated predators-inspired effects persisted beyond the immediate ‘fight-or-flight’ response and remained measurable more than a week later.
“These results have important implications for biomedical researchers, mental-health clinicians, and ecologists,” Zanette said. The findings support the notion that PTSD is not unnatural, and that its long-lasting effects on fertility and survival are the norm in nature.
Retaining a powerful enduring memory of an encounter with a life-threatening predator is clearly evolutionarily beneficial; that memory helps avoid such events in the future. However, a growing number of biomedical researchers has begun to propose PTSD as the cost of that memory.
Ecologists are recognizing predators affect prey not just by killing them, but also by scaring them. For example, Zanette and her collaborators have shown in a previous study that scared parents are less able to care for their young.
The long-lasting effects of fear on the brain demonstrated in this new study suggest predator exposure could impair parental behaviour for a prolonged period thereafter with greater negative effects on offspring survival than previously believed.
The team conducted the study on wild-caught, black-capped chickadees at Western’s Advanced Facility for Avian Research (AFAR).
For two days, individual birds were exposed to recordings of either predators or non-predators and then housed together in flocks outdoors for seven days. During that time, they were not exposed to any further recordings.
After seven days, fearful behaviour was measured in each bird’s reaction to hearing a chickadee alarm call. The long-lasting effects on the neural circuitry of fear were assessed by measuring the levels of a genetic transcription factor in the brain (amygdala and hippocampus).