Can animals suffer from PTSD

Wild animals also have PTSD

When wild animals are confronted with a predator, their reaction goes far beyond the classic "fleeing or fighting", as a study with titmice has now revealed. Because days or even weeks later, the animals show symptoms that are amazingly similar to those of post-traumatic stress disorder (PTSD) in humans. This underlines that PTSD is not an unnatural, purely human phenomenon, but also occurs in nature, the researchers emphasize.

Whether it is an accident, war or other emotionally serious situations: Those who experience life-threatening events often do not emerge without lasting consequences. Many people continue to suffer weeks, months or even years later from insomnia, anxiety attacks, excessive nervousness and alertness and in many cases also from depression or aggression. Such a post-traumatic stress disorder is often interpreted as a derailed, abnormal reaction of the psyche to the extreme stress of the triggering situation.

Do wild tits suffer from PTSD?

But is this reaction to traumatic events really "unnatural"? After all, it has long been known that experimental animals such as mice can react to frightening situations such as the presence of a cat or the smell of a predator with similar persistent symptoms. "We now know that life-threatening events can have lasting effects on the brain and behavior," explain Liana Zanette from Western University in London and her colleagues. And this phenomenon has now also been observed in many laboratory animals.

So far, however, it has remained unclear whether this is a consequence of keeping in captivity and breeding or whether symptoms similar to PTSD also occur in wild animals. Zanette and her team have now investigated whether this is the case in wild black-capped tits (Poecile atricapillus). In the experiment, they exposed these relatives of our domestic tits to the calls of various birds of prey, which are among the most common predators of these songbirds, for two days. Instead, a control group heard the calls of harmless animals such as frogs and other songbirds. The tits were then returned to the swarm for seven days.

Increased startle response and anxiety indicators in the brain

Then the actual test followed: the researchers exposed the tits to the typical warning calls of their species and observed how the birds behaved. Would the birds show the exaggerated fear response typical of PTSD? In fact, the tits that had been exposed to the calls of the birds of prey a week earlier showed a much more fearful behavior than their conspecifics: They spent six times more time sitting there frozen, motionless but highly vigilant, as Zanette and her colleagues report.

There were also measurable changes in the birds' brains: seven days after the traumatic experience, the two brain areas involved in the fear circuit, the amygdala and the hippocampus, showed an almost 50 percent higher activity of a marker typical of fear reactions. "To the best of our knowledge, this is the first experiment to demonstrate that the fear induced by predators can cause persistent effects on the amygdala and hippocampus of a wild animal," say Zanetti and her colleagues. According to them, changes in the behavior and brains of the tits they observed are a clear indication that these birds may also suffer from some type of post-traumatic stress disorder.

A natural phenomenon

But what does this mean from a biological point of view? As the researchers explain, such a PTSD reaction in a wild animal can have negative consequences for its ecological fitness. Because a tit that is constantly in a state of fright, has less time to look for food or to look after mating and offspring. On the other hand, excessive vigilance in the presence of many predators can also help to improve the chances of survival. PTSD in wild animals would therefore be a natural response that, while having a biological cost, can improve survival in certain situations.

"Our results support the assumption that PTSD is not unnatural and that such long-lasting consequences of the fear caused by predators could even be the norm in nature," says Zanette. "This also has important consequences for psychology, biomedical research and ecology."

Source: University of Western Ontario; Technical article: Scientific Reports, doi: 10.1038 / s41598-019-47684-6

August 9, 2019

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