Sick chimps seek out medicinal plants to heal themselves, study finds

Wild chimpanzees actively seek out plants with medicinal properties to treat themselves for specific ailments,a new study has found.

While most animals consume foods with medicinal properties as part of their routine diet, few species have been shown to engage in self-medication in a way that suggests they have basic awareness of the healing properties of the plants they’re feeding on.

Until now, the challenge has been to distinguish between normal consumption of food that has medicinal value, on the one hand, and ingesting such foods for the purpose of treating a condition, on the other.

“Self-medication has been studied for years, but it has been historically difficult to push the field forward, as the burden of proof is very high when attempting to prove that a resource is used as a medicine,” Elodie Freymann, a scientist at the University of Oxford in the U.K. and lead author of the study, told Mongabay in an email.

To deal with the challenge, the study adopted a multidisciplinary approach, combining behavioral data, health monitoring, and pharmacological testing of a variety of plant materials chimpanzees feed on. It pooled together 13 researchers comprising primatologists, ethnopharmacologists, parasitologists, ecologists and botanists.

According to the study, pharmacological data interpreted on its own is important for establishing the presence of medicinal resources in chimpanzee diets. However, this study also relied on observational information and health monitoring to determine whether chimps were deliberately self-medicating.

Over a period of eight months, the scientists monitored the feeding behaviors of two communities of chimpanzees (Pan troglodytes) familiar with humans around them in Budongo Forest in Uganda.

They collected samples from plant parts associated with chimpanzee behaviors that previous research had flagged up as possibly linked to self-medication: consuming bark, dead wood and bitter pith.

The researchers collected samples from 13 plant species known to be consumed at least occasionally by the Budongo chimpanzees, testing the samples for their ability to suppress bacterial growth and inflammation (testing for antiparasitical properties was beyond the scope of the study).

The researchers also tracked the health of individual chimpanzees, analyzing fecal matter and urine and monitoring individuals with wounds, parasite infestations or other known ailments.

They observed that individuals with injuries or other ailments such as parasite infestations, respiratory symptoms, abnormal urinalysis or diarrhea ingested plants or parts of plants that laboratory testing found to have healing properties.

“We describe cases where chimpanzees with possible bacterial infections or wounds selected bioactive plants,” Freymann said. “We also describe cases where wounded individuals selected rarely consumed plants with demonstrated anti-inflammatory properties — suggesting they could be ingesting plants to aid in wound-healing, a novel finding.”

In addition, unlike previous studies that focused on single plant resources, this one identified 13 species with medicinal potential.

“This greatly expands what we know about chimpanzee medicinal repertoires. This study also highlights the unique medicinal repertoires of two chimpanzee communities with no previous systematic research on their self-medication behaviors,” Freymann said.

According to Freymann, identifying plants that could have medicinal value for chimpanzees is important for the conservation of the species.

“If we know which plants chimpanzees need to stay healthy in the wild, we can better protect these resources to ensure chimpanzees have access to their wild medicine cabinets,” she said. “If these plants disappear, it could leave our primate cousins susceptible to pathogens they could previously defend against.”

This is also important, Freymann said, because “we could learn from the chimpanzees which plants may have medicinal value which could lead to the discovery of novel human drugs.”

The study adds to a growing body of research on primates using medicinal plants to treat sickness. In another recent report, a wild orangutan in Sumatra was observed treating a facial wound with a plant known for its healing properties. Erin Wessling, co-lead of the working group on chimpanzee cultures at the IUCN, the global wildlife conservation authority, said part of the reason for the recent attention to these types of medicative behaviors is because they’re relatively rare and can only be identified in species that have been closely monitored over long periods of time.

“It takes years to be able to watch apes in the wild to this level of detail, and even more years after that to be able to identify with any certainty what are core components of an ape’s diet versus the much more rare medicinal use cases,” she said.

Wessling, who was not part of the study, told Mongabay that while it’s been known that chimpanzees have these rare cases of medicinal use, scientists are finally getting to a level where they can point to self-medication as a widespread and diverse behavior used across medicinal contexts.

She said the Budongo study “points out really nicely that conservation is more than just a numbers game — that there’s real value in thinking about how organisms interact with the ecosystems they reside in, and that even the most uncommon components of those ecosystems can be critical for an organisms’ survival.

“Further, results such as these offer a nice insight into the intrinsic value of chimpanzees, demonstrating what we’ve suspected for a long time — that chimpanzees have the capability to recognize and treat an ailment with plants that have natural (and measurable) medicinal properties,” Wessling said.

“It shows we have a great deal left to learn about the natural world, not only our ape cousins, and provides even more reason to make sure there is a future for them.”

The chimp doctor will see you now: Medicating apes boost the case for conservation

Citation:

Freymann E, Carvalho S, Garbe LA, Dwi Ghazhelia D, Hobaiter C, Huffman MA, et al. (2024). Pharmacological and behavioral investigation of putative self-medicative plants in Budongo chimpanzee diets. PLOS ONE, 19(6), e0305219. doi:10.1371/journal.pone.0305219

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