Many of us are quite concerned about the destruction of the natural world. It turns out that it’s not just people who experience stress. When analyzing hormones that accumulate in the fur, the researchers found that rodents and marsupials that live in smaller areas of the South American Atlantic forest are more exposed than those that live in more intact forests.
“We suspected that organisms in deforested areas in pristine forests were more stressful than animals, and we found evidence of this,” said Noé de la Sancha, research fellow at the Field Museum in Chicago, associate professor of biology at Chicago State University and co-author of a new paper in Scientific Reports detailing the discovery. “Small mammals, especially rodents and small marsupials, tend to be more stressed in smaller forest areas or have more evidence of higher levels of stress hormones than in larger forest areas.”
“Many species around the world, especially in the tropics, are under-discussed,” said Sarah Boyle, associate professor of biology and chair of the environmental studies and sciences program at Rhodes College and lead author of the study. “Not much is known about many of these animals in terms of basal hormone levels.”
The Atlantic forest is often overshadowed by its neighbor, the Amazon, but it is South America’s second largest forest, stretching south from northeastern Brazil along the Brazilian coast to northwestern Argentina to eastern Paraguay. It once covered approximately 463,000 square miles, an area larger than California, Oregon, Washington, and Nevada combined. Since the arrival of Portuguese colonists 500 years ago, parts of the forest have been destroyed to make way for arable land and urban areas. Today less than a third of the original forest has been preserved.
Destroying an animal’s habitat can dramatically change its life. There is less food and territory, and the animal may have more contact with predators or increased competition with other animals for resources. These circumstances can lead to long-term stress.
Stress is not a bad thing in and of itself – in small doses, stress can save lives. “A stress response usually tries to rebalance your body,” says David Kabelik, associate professor of biology and chairman of the Neuroscience program at Rhodes College and one of the authors of the paper. “When something is bothering you and you may get injured or die, the stress response mobilizes energy to deal with the situation and get things back to normal. It enables you to survive.” For example, when an animal encounters a predator, a flood of stress hormones can give it the energy it needs to run away, and then those hormone levels go back to normal. “But then these animals are brought into these small fragments of their habitat, where they are exposed to increased stress over long periods of time. This can lead to diseases and dysregulation of various physiological mechanisms in the body.”
For this study, the researchers focused on forest areas in eastern Paraguay, which were particularly hard hit in the last century, as the region was clear for firewood, livestock and soy. To study the effects of this deforestation, researchers captured 106 mammals from areas ranging from 2 to 1,200 hectares – from the size of a city block to 4.63 square miles. The creatures they analyzed included five species of rodents and two species of marsupials.
The researchers took samples of the animals ‘fur because hormones could accumulate in the hair over many days or weeks and provide a clearer picture of the animals’ typical stress levels than the hormones found in a blood sample. “Hormones change in the blood from minute to minute, which doesn’t really reflect whether these animals are under long-term stress or whether they ran away from a predator a minute ago,” says Kabelik, “and it was us.” try to get at something that is more of an indicator of long-term stress. Because glucocorticoid stress hormones build up in the fur over time, analyzing these samples allows you to look at a longer-term measure of their stress levels. “
Back in the laboratory, the researchers ground the fur into a fine powder and extracted the hormones. They analyzed the hormone levels using an enzyme immunoassay: “They use antibodies that bind these hormones to find out how many there are,” says Kabelik. “Then you divide that by the amount of fur that was in the sample and it tells you the amount of hormones that are in per milligram.”
The team found that the animals from smaller forest areas had higher levels of glucocorticoid stress hormones than animals from larger forest areas. “Our findings that animals in the small forest areas had higher glucocorticoid levels were not surprising, as some of these forest areas were severely affected by forest loss and fragmentation,” says Boyle.
“These results are particularly relevant to countries like Paraguay, which currently have an accelerated rate of change in natural landscapes. In Paraguay we are only just beginning to document how the biodiversity that is being lost is distributed,” says Pastor Pérez, biologist at the Universidad Nacional de Asunción and another author of the work. “However, this paper shows that we also have a lot to learn about how these species interact in these environments.”
The scientists also found that the methods used to capture the animals contributed to the amount of stress hormones present. “It’s an important consideration that people need to understand when doing these studies. If they catch the animals live, it can affect the measured hormone levels,” says Kabelik.
Not only does the study shed light on how animals react to deforestation, but it could also provide a better understanding of the circumstances in which animals can transmit diseases to humans. “If you have a lot of stressed mammals, they can harbor viruses and other diseases, and there are more and more people living near these deforested areas who could potentially come into contact with these animals,” says de la Sancha. “By destroying natural habitats, we may create hotspots for zoonotic outbreaks.”
And the researchers say the results of this study go well beyond the South American Atlantic forest.
“By and large, this is really important as it could be applicable to forest debris around the world,” says de la Sancha. “The tropics have the greatest diversity of organisms on the planet. Therefore, this has the potential to affect the greatest diversity of living organisms on the planet as more and more deforestation occurs. We will see individuals and populations that tend to grow too demonstrate.” higher levels of stress. “
