Can animals actively seek out a plant to heal a parasitic infection or to numb pain? For years scientists have presumed that such activity was restricted to animals capable of more complex cognitive abilities, like chimpanzees. However scientists have described incidents of fruit flies (1), caterpillars (2) and butterflies (3) “self medicating” to prevent or cure parasitic infections, suggesting that such behavior may be both innate as well as learned.
As early as 1978, D.H. Janzen pointed out that many animals avoid specific plants either innately or by learning because of their effects on fitness, and he asked the question, “is it possible that animals seek out plant parts by way of writing their own prescriptions?” (4). He described stories of elephants eating a particular legume, colobus monkeys in Kibale forests with low numbers of parasites, and pigs eating pomegranate roots, presumably for anti-helminthic effects.
During a 1987 expedition, Michael Huffman, a primate researcher at Kyoto University, noticed a mother chimp that was lying ill on a bed of branches while he was out on a field study. Eventually the mother chimp climbed to the ground and deliberately walked to a shrub known to the local tribe as “Mjonso”. The chimpanzee tore off several branches, removed the bark, chewed on the inner portion of the branches and sucked the juice. This behavior was unusual. In years of observing chimpanzees, Huffman had never seen a chimp eat this particular plant—let alone seek out a certain section of the plant. The tribe member accompanying Huffman on the exhibition told Huffman that this shrub was used by the tribe for medicine, for stomachaches, malarial fevers, and intestinal parasitic infections. Huffman quickly realized that he may have just witnessed an animal “self-medicating”, and further studies in the field allowed him to observe other chimps using the same plant to cure themselves of ailments (5).
Evidence of self-medication and medication of others among insect populations has been more recent and includes examples of prophylactic treatments (reviewed in 6). Kacsho and colleagues published a study in 2013 describing a behavioral immune response in which fruit flies prophylactically “treat” the next generation in response to the presence of female parasitic wasps (1). In the presence of female wasps (but not males or pupae) the fruit fly will preferentially lay eggs in an area of higher ethanol concentrations. Interestingly, this group was able to identify a couple of proteins involved in the process, one of which is a regulator of the alcohol dehydrogenase gene, the transcription factor Adf1. Adf1 expression is required for long term memory as well. Flies expressing a mutant form of Adf1 that affects long term memory “forgot” seeing female parasitic wasps when they were transferred to wasp-free cages and did not lay eggs on ethanol-containing food, unlike wild type flies that were able to “remember” exposure to the female wasps. The authors conclude that a single protein may be involved in long term memory formation and regulating tolerance to ethanol, a compound which normally reduces fitness, but protects against parasitic wasp infections (1). These may be the first pieces of a behavioral immune response pathway.
Is there anything to be gleaned from learning about self-medication in chimpanzees and fruit flies?
As Janzen also observed in his 1978 report:
“The plant world is not colored green; it is colored morphine, caffeine, tannin, phenol, terpene…” (4)
Perhaps there is tremendous value in gaining an increased understanding of the our world by looking at “what is in a tree from the viewpoint of a monkey, sloth or koala” (4). We can learn more about the many and varied compounds produced by plant species and their effects on parasites, protozoans, and microbes by observing how these “animal pharmacists” use them. We may how to more effectively manage livestock, since access to plants that contain antiparasitic compounds can improve livestock health (5, 7,8). We may also learn more about bee decline and colony health (9). And, since some of the more recent studies are describing the molecular mechanisms and cellular signaling underlying the behavioral immune responses that drive these self-medication activities, we may also learn more about how the genes and proteins within our own cells interact, allowing us to gain a better understand human biology.
2024 Addendum: Orangutans Exhibit Self-Medication Behavior | AnnaKay Kruger
Research published May 2024 in Nature (10) revealed evidence of self-medication in wild orangutans, adding another species to the list of animals known to engage in this behavior. In Sumatra, a male orangutan was observed treating a facial wound with a poultice made from the leaves of the Fibraurea tinctoria plant, which is known in the area for its medicinal properties. While self-medication has been seen in many species, this study is notable as it provides the first systematic documentation and compelling scientific evidence.
In June 2022, a research team in Sumatra noticed that the orangutan in question, Rakus, had a wound on his right cheek, possibly acquired during a fight. The team watched Rakus feed on the woody stem and the leaves of the evergreen creeper Akar Kuning (Fibraurea tinctoria). This plant is used by locals for its analgesic, antipyretic and diuretic effects, among others, though it is rarely eaten by orangutans. In addition to the ingestion of the plant, researchers saw Rakus chew the leaves without swallowing and create a sort of compress out of the chewed material, which he placed on the open wound. After eight days, the wound had healed.
Investigations into the chemical properties of the plant demonstrated the presence of compounds like furanoditerpenoids, protoberberine alkaloids, jatrorrhizine and palmatine, which together offer benefits including antibacterial, anti-inflammatory, antioxidant, narcotic, antidiabetic and anticarcinogenic activity.
The results of this research further support the assertion that self-medication may be widespread and varied across the animal kingdom. Our continued study of this type of behavior can enhance our understanding of the mechanisms used in self-medicating, and how intentional it is—for instance, Rakus’s use of Akar Kuning appears intentional in this study as he uses his poultice only on his wound and repeats the behavior several times. What sorts of underlying mechanisms animals use to recognize and apply substances with medicinal properties, as well as how this knowledge is acquired (whether through social or individual learning) are questions that will require further research.
Literature Cited
- Balint, Z. et al. (2013) Fruit flies medicate offspring after seeing parasites. Science 339, 947–950.
- Singer, M.S., Mace, K.C. and Bernays, E.A. et al. (2009) Self-medication as adaptive plasticity: increased ingestion of plant toxins by parasitized caterpillars. PLOS One 4, e4796.
- Lefèvre, T. et al. (2010) Evidence for transgenerational medication in nature. Ecol. Lett. 13, 1485.
- Janzen, D.H. (1978) Complications in interpreting the chemical defenses of tress against tropical arboreal plant-eating vertebrates. IN: The Ecology of Arboreal Folivores Montgomerie, G.C., ed. (Smithsonian Institution Press, Washington, D.C.)
- Oosthoek, S. (2014). Wild medicine Student Science. https://student.societyforscience.org/wild-medicine.
- de Roode, J.C., Lefèvre, T. and Hunter, M.D. (2013) Self-Medication in Animals. Science 340, 150–151.
- Amit, M. et al. (2013) Self-medication with tannin-rich browse in goats infected with gastro-intestinal nematodes. Vet. Parasitol. 198, 305–11.
- Villalba J.J. and Provenza F.D. (2007) Self-medication and homeostatic behaviour in herbivores: learning about the benefits of nature’s pharmacy. Animal 9, 1360–70.
- Simone-Frinstrom, M.D. and Spivak, M. (2012) Increased resin collection after parasite challenge: a case of self medication in honey bees? PLOS One 7, e34601.
- Schuppli, Caroline, et al. “Active Self-Treatment of a Facial Wound with a Biologically Active Plant by a Male Sumatran Orangutan.” Scientific Reports, vol. 14, 2024, https://doi.org/10.1038/s41598-024-58988-7.
Michele Arduengo
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