Los chimpanzees Wild animals sometimes eat plants that can treat or alleviate the symptoms of a disease, but it is difficult to establish whether they do so intentionally, although the results of a new study suggest that they do seek out specific plants for their medicinal effects.
The study published by Plos One coincides with the publication in Science of another article that points out how a devastating hurricane in Puerto Rico changed the norms of social behavior of macaque colonies, which became more tolerant of their peers.
Research on chimpanzees, led by the University of Oxford (United Kingdom), indicates that when they are sick they eat tree bark, dead wood and ferns with antibiotic and anti-inflammatory effects.
The authors combined observations of the behavior of chimpanzees (Pan troglodytes) with pharmacological tests of the potentially medicinal plants they eat, observing the behavior and health of 51 specimens from two communities in the Central Budongo Forest Reserve, in Uganda.
Additionally, they collected plant extracts from 13 species of trees and herbs in the reserve that they suspected the chimpanzees might use for self-medication, and analyzed their anti-inflammatory and antibiotic properties.
Among them were plants that sick or injured chimpanzees had been observed eating and that were not part of their normal diet, and others that, according to previous research, could be consumed for their medicinal properties.
The researchers found that 88% of the plant extracts inhibited bacterial growth, while 33% had anti-inflammatory properties.
Over 116 days of field observation, the researchers recorded several unusual feeding episodes and self-medication-like behaviors.
Thus, a male chimpanzee with an injured hand foraged and ate fern leaves, which could have helped reduce pain and swelling, and an individual with a parasitic infection ate catthorn bark (Scutia myrtina).
“Whether these resources are consumed intentionally as a form of therapeutic self-medication or passively as medicinal foods should be evaluated on a case-by-case basis, taking into account behavioral observations,” the researchers write.
Medicinal plants growing in the Central Budongo Forest Reserve could also be useful for the development of new drugs to address the challenges of antibiotic-resistant bacteria and chronic inflammatory diseases, the authors suggest.
The second study focuses on the behavior of a population of rhesus macaques on Cayo Santiago, known as Monkey Island, where 63% of the vegetation was destroyed by Hurricane María, which hit Puerto Rico in 2017 and killed more of 3,000 people.
The island’s tree cover remains well below pre-hurricane levels and the heat makes shaded areas a rare and precious resource for the macaques.
“In response to the drastic changes caused by the hurricane, the macaques persistently increased tolerance and decreased aggression among themselves,” said Camille Testard, from the University of Pennsylvania (USA) and one of the signatories.
The greater tolerance allowed more macaques to access the scarce shade, which is essential for survival.
After the hurricane, macaques that showed above-average social tolerance and were better able to share the shade were 42% less likely to die than those that were less tolerant.
These monkeys “are not the best at sharing resources, whether food or shade” and are known to live in an “aggressive and highly competitive” society, Professor Lauren Brent, from the University of Exeter, explained in a statement.
Social behavior was assessed by recording aggression and the frequency with which individuals were seen sitting together. To access the shadow, they have to tolerate others and be tolerated by them, and this tolerance extends to other everyday interactions.
The macaques that began sharing the shade also spend time together in the mornings, before the heat of the day forces them to seek shade. Thus, the hurricane changed the rules of the game in monkey society.