February, 2000: Tanzania
Observations of chimpanzees' feeding behavior in Tanzania, East Africa, have led to the discovery of medicinal properties and other potential applications for two types of plants. This type of study, involving the ways animals use plants, is referred to as zoopharmacognosy, a term coined in 1992 from Greek roots: zoo- = animal; pharma- = a drug or poison; and -cognosy = to recognize.
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Chimp eating Vernonia. (Photo © M.A. Huffman.)
While conducting such a study in Tanzania's Gombe National Park, Harvard University graduate student Richard Wrangham noticed chimps selecting and eating the leaves of Aspilia sp. (Other scientists have since studied chimps in other areas, including the Mahale Mountains.) The three main species selected were A. mossambicensis, A. pluriseta, and A. rudis. Other researchers noticed chimps selecting and eating the pith of Vernonia amygdalina. In both cases, these were obviously not appealing food choices for the chimps because they grimaced when swallowing the leaves, and the pith is known to be very bitter.
Interestingly, it was noted that not all chimps practiced "whole leaf swallowing" and "bitter pith chewing," as scientists now refer to those practices. Furthermore, Michael Huffman of the Primate Research Institute at Kyoto University noted that the chimps practicing these behaviors were in poorer health than the others. Specifically, they seemed depressed and despondent, tended to separate themselves from the group, and had diarrhea. This observation led to the hypothesis that Aspilia and Vernonia were consumed in response to illness, possibly parasitic infestation. In 1989, Huffman and his collaborators tested this hypothesis by collecting and analyzing fecal samples and documenting chimp activity for as many individuals as possible. Fecal analysis revealed that chimps practicing whole leaf swallowing and/or bitter pith chewing were in fact suffering from single or multiple parasitic infections.
Vernonia pith was examined via bioassay, a technique in which living material in a system is tested for biological activity. The tests showed antiparasitic activity against microorganisms that infect both chimps and humans. Further analysis of the bitter pith revealed chemicals categorized as sesquiterpene lactones and steroid glycosides, both of which are known for their bioactivity. Specifically, vernonioside B1 and vernoniol B1, two compounds isolated from the pith of Vernonia, suppressed movement and egg-laying activity in bioassays of Schistosoma japonicum, a parasitic worm. Thus, apparently the chimps were selecting Vernonia for its chemical constituents.
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Trichomes on Oxalis sp. (X500). (SEM © 1999 Erica Kipp.)
A different mode of action was found for Aspilia. When the fecal samples of chimps consuming those leaves were analyzed, not only did the feces contain a stable number of parasites during Aspilia consumption, but the parasitic worms (Oesophagostomum stephanostomum) were still very much alive. Obviously, consuming the plant had suppressed neither the movement nor the egg-laying activity of the parasitic worms. However, the analysis also revealed that Aspilia leaves not only remained whole and undigested, but were curiously folded like accordions--a characteristics that turned out to have a function: O. stephanostomum attach their suckers to the intestine's mucous lining, where they extract nutrients from the host. In this case, the intestinal worms were firmly stuck to the surface of the leaves (which are known to have a high concentration of trichomes, or hairs) and caught between the accordion-like folds! Clearly this was a physical removal of the parasites as the roughness of the leaf surface seemed to dislodge the worms from the animal's intestinal lining.
Aspilia is a dicot in the Compositea or Asteraceae family, and its distribution includes tropical America, Africa, and Madagascar. Although leaf swallowing basically results in the physical removal of intestinal worms, additional research into the chemical composition of Aspilia's parts other than the leaves has indicated the production of a red oil called thiarubrine-A. This chemical has been found to inhibit the growth of many disease-causing agents, specifically parasitic worms, microorganisms, and other intestinal parasites.
Vernonia is also in the Asteraceae family, with a similar distribution to that of Aspilia. Its sesquiterpene lactones have demonstrated anti-tumor activity, and the Vernonia chemicals (vernoniosides) of the pith have proven effective against drug-resistant malarial parasites, which are very common within the range of this plant.
Although the chimpanzees pointed the way to Aspilia and Vernonia, plants overlooked in the past, additional research has revealed that Aspilia and Vernonia have been part of Tanzanian folk medicine for hundreds of years. The WaTongwe traditionally use Vernonia for stomachaches and several parasitic infections. A. latifolia has been reported to stop bleeding by inducing clot formation. The leaves of Vernonia are highly toxic and apparently avoided by the chimps; however, after soaking the leaves in water and cooking them, local people use them in soup and stew as a strength-giving tonic. They also widely use Vernonia to treat parasites and other ailments in themselves and their livestock, indicating potential agricultural applications for other countries. Additionally, it is documented that Vernonia is used locally as an insecticide.
Apparently we can learn much from watching our neighbors on planet Earth!
References, Websites, and Further Reading
Ohigashi, H., et al. 1994. Toward the chemical ecology of medicinal plant use in chimpanzees: The case of Vernonia amygdalina, a plant used by wild chimpanzees possibly for parasite-related diseases. Journal of Chemical Ecology 20(3):542-53.
Huffman, M., et. al. 1994. Ethnobotany and zoopharmacognosy of Vernonia amygdalina, a medicinal plant used by humans and chimpanzees. Proceedings of the International Compositae Conference, Kew 2:351-60.
Page, J.E., et. al. 1997. Chemical basis for Aspilia leaf-swallowing by chimpanzees: A reanalysis. Journal of Chemical Ecology 23(9): 2211-26.
Gombe National Park and Jane Goodall's work
Homepage for the chemo-ethology of hominid interactions with medicinal plants and parasites
Ecological and demographic data on field research studies with chimps
Stern, Introductory Plant Biology, 8th Edition
Chapter 8: Flowers, Fruits, and Seeds
Information on dicots, pp. 129-32
Chapter 11: Growth
Bioassay used for hormone concentration measurement, pp. 188-91
Chapter 17: Kingdom Monera and Viruses
Information on bacteria and viruses, pp. 280-303
Chapter 24: Flowering Plants and Civilization
Asteraceae family, pp. 453-54
Chapter 25: Ecology
Populations; herbivore-animal interactions, pp. 463-67
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