What animals can teach us about stress

Humans, being essentially self-centred, want to know what makes them different from their wild relatives, as well as what similarities exist. But it’s not just a matter of curiosity. Other species can teach us a lot about the big issues that challenge us in modern society.

Stress is seen as a pervasive modern-day killer. It has an impact on everything from our intestinal processes to our cherished cognitive performance. But stress is not a modern thing. All animals stress about predators, hunger, and lack of sex. So, what can we learn from them?

If there were a sweet spot – the optimal stress level – at which most stressed animals show peak cognitive performance we could possibly use the information to modulate our own stress and mental feats. And it would be brilliant if we could develop a deep understanding of how wild animals perform under varying levels of risk, given that they have evolved to deal with these over millions of years.

Studying the link between stress and cognitive performance, however, is hampered by many challenges. Although our methods of measuring stress have improved dramatically in recent years, outside the lab it’s still very difficult to contrast chronic stress from, say, a long drought, versus acute stress, such as the presence of a predator. Or linking our measures of stress to wild animals' learning and memory skills.

We’re only just scratching at the surface of this problem.

Not stressing the animals

The study of stress itself is coming into its own. Traditionally, researchers actually increased their study subjects' stress levels by the collection of blood used to measure circulating stress hormone (cortisol) levels. More recently, though, we have been given a barrage of less invasive tools with which to measure animals’ anxiety.

Perhaps the most widely used technique is to extract hormonal data from fecal samples. There is no need to catch or handle the animal. By happy coincidence stressed animals produce even more poo than their calm counterparts. Fecal hormones have certainly confirmed many of our suspicions. Animals become more stressed when they are handled and in captive conditions like zoos. They also find losing a friend very stressful.

There have also been some surprise findings. It may seem obvious that being a subordinate animal is stressful, but research on baboons shows that alpha males may actually be the ones heading for a stomach ulcer.

Another way of indirectly assessing anxiety is by measuring changes in how much food wild animals leave behind in experimental feeding patches. The idea is that a relaxed animal will eat more of the food than an anxious individual, leaving behind more food. This is called the giving up density. Experiments such as these allow us to clearly see how wild animals perceive variation in risk in their natural landscapes.

We know from Giving Up Density experiments that Nubian ibex perceive increased tourism as risky, while samango monkeys use human observers as potential shields against predators, eating much more food when their human “guards” are nearby. These same monkeys also feel much more threatened near the ground, compared to positions higher up under the tree canopies.

An even more exciting recent development is the measure of stress through thermal imagery. Researchers are knee-deep in the development of reliable techniques using thermal cameras to detect rapid changes in body surface temperatures.

A spike in stress levels causes blood to shunt away from an animal’s body surface (may this be what gives us the chills when we panic?). Suddenly, and quite literally, the animal appears to be cooler. Armed with this knowledge, we may be able to monitor fluctuation in stress levels in real time.

With all of these tools at our disposal, you may imagine that we know everything there is to know about wild animals’ performance under pressure. Unfortunately we don’t.

There is still a lot to learn

Our knowledge of cognitive performance and stress is heavily skewed towards lab rats. A great deal has been learnt from them.

For example, experiments have shown some positive effects of stress on lab rats. Brief, acute stress can actually lead to an increase in neurons in rats' brains. And rats who were stressed out as teenagers become more impulsive as adults, which can make them more effective foragers, especially under high risk conditions.

In some ways, these findings sound like great news. We can perhaps all relate to the idea that we perform rather well when the stressful situation is short-lived, but flunk out when the pressure is either non-existent or overwhelming. But what we can say about these very rodent-focused studies is that it’s time to move beyond rodents and beyond the lab.

Moving past rodents

Data are slowly trickling in.

Studies on wild animals appear to confirm the idea that long-term, chronic stressors can truly decrease your mental acuity. For example, a recent study on wild-caught guppies showed that those used to stress make a lot more mistakes in cognitive challenges compared to the relatively relaxed fish.

Left-handed marmosets, which are the target of more social attacks and are therefore perhaps more chronically stressed, also show negative cognitive biases compared to their right-handed group members.

Marmosets don’t function well cognitively in stressful situations.Reuters

In my own lab we are trying to assess various ways in which varying risk can affect learning abilities. We are using Giving Up Density experiments to determine how well wild bat-eared foxes may perform in low-risk and high-risk situations.

The key to unlocking how animals deal with stress requires that we step off our pedestal and acknowledge that other animals may outdo us in some cognitive tasks. If we do this we may learn how to truly cope in our own rapidly changing landscape.

Aliza le Roux receives funding from the National Research Foundation (South Africa). She is affiliated with the University of the Free State's Qwaqwa campus, and member of the South African Young Academy of Science.