Zoopharmacognosy

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For use of psychoactive substances by animals for pleasure, see Recreational drug use in animals.
For the effect of
psychoactive drugs on animals conducted via animal testing, see Effect of psychoactive drugs on animals
.
See also: Venom § Venom resistant animals
A cat eating grass – an example of zoopharmacognosy

Zoopharmacognosy is a behaviour in which non-human animals self-medicate by selecting and ingesting or topically applying plants, soils and insects with medicinal properties, to prevent or reduce the harmful effects of pathogens, toxins, and even other animals.[1][2] The term derives from Greek roots zoo ("animal"), pharmacon ("drug, medicine"), and gnosy ("knowing").

An example of zoopharmacognosy occurs when dogs eat grass to induce vomiting. However, the behaviour is more diverse than this. Animals ingest or apply non-foods such as

parasitic infestation or poisoning.[3]

Whether animals truly self-medicate remains a somewhat controversial subject because early evidence is mostly circumstantial or anecdotal.[4] However, more recent examinations have adopted an experimental, hypothesis-driven approach.

The methods by which animals self-medicate vary, but can be classified according to function as prophylactic (preventative, before infection or poisoning) or therapeutic (after infection, to combat the pathogen or poisoning).[4] The behaviour is believed to have widespread adaptive significance.[5]

History and etymology

In 1978, Janzen suggested that vertebrate herbivores might benefit medicinally from the secondary metabolites in their plant food.[6]

In 1993, the term "zoopharmacognosy" was coined, derived from the Greek roots zoo ("animal"), pharma ("drug"), and gnosy ("knowing").[7] The term gained popularity from academic works[4] and in a book by Cindy Engel entitled Wild Health: How Animals Keep Themselves Well and What We Can Learn from Them.[8]

Mechanisms

The

deglutition or ingestion. First, ingested material may have pharmacological antiparasitic properties, such as phytochemicals decreasing the ability of worms to attach to the mucosal lining of the intestines or chemotaxis attracting worms into the folds of leaves. Additionally, many plants have trichomes, often presented as hooked and spiky hairs, that can attach to parasites and dislodge them from the intestines. Another possible mode of action is that the ingested material may initiate a purging response of the gastrointestinal tract by rapidly inducing diarrhoea. This substantially decreases gut transit time, causing worm expulsion and interruption in the life cycle of parasites. This, or a similar, mechanism could explain undigested materials in the faeces of various animals such as birds, carnivores and primates.[9]

The

topical application of materials is often used by animals to treat wounds or repel insects.[10] When plant leaves are chewed and then directly rubbed onto fur, compounds from said leaves are released for use. These compounds can often be analgesic or antiparasitic in nature. In regards to an insect repellant, the secondary metabolites traditionally used by plants to deter herbivores and insects from eating them[11] can be used by animals as a protective measure. By interfering with neuroreceptors, these secondary metabolites can specifically act as olfactory cues for insects to avoid a certain source.[12]

Methods of self-medication

The three reported methods of self-medication are deglutition, ingestion, and topical application. When using one of these methods while appearing well, an animal may be using self-medication as a

prophylactic measure. When it is unwell, the animal could be using self-medication as a curative
measure.

Deglutition

Some examples of zoopharmacognosy are demonstrated when animals, namely apes, swallow materials whole instead of chewing and ingesting them.

Chimpanzees

Wild chimpanzees sometimes seek leaves of the Aspilia plant. These contain thiarubrine-A, a chemical active against intestinal nematode parasites. Because this compound is quickly broken down by the stomach, chimpanzees will pick up the Aspilia leaves and, rather than chewing them, they roll them around in their mouths, sometimes for as long as 25 seconds. They then swallow the capsule-like leaves whole. Afterwards, the trichomes of the leaves can attach to any intestinal parasites, namely the nodular worm (Oesophagostomum stephanostomum) and tapeworm (Bertiella studeri), and allow the chimpanzee to physically expel the parasites.[13] As many as 15 to 35 Aspilia leaves may be used in each bout of this behaviour, particularly in the rainy season when there is an abundance of many parasitic larvae that can cause an increased risk of infection.[14]

Chimpanzees sometimes eat the leaves of the herbaceous

Desmodium gangeticum. Undigested, non-chewed leaves were recovered in 4% of faecal samples of wild chimpanzees and clumps of sharp-edged grass leaves in 2%. The leaves have a rough surface or sharp-edges and the fact they were not chewed and excreted whole indicates they were not ingested for nutritional purposes. Furthermore, this leaf-swallowing was restricted to the rainy season when parasite re-infections are more common, and parasitic worms (Oesophagostomum stephanostomum) were found together with the leaves.[9]

Bonobos sometimes swallow non-chewed stem-strips of

Manniophyton fulvum. Despite the plant being abundantly available all year, M. fulvum is ingested only at specific times, in small amounts, and by a small proportion of bonobos in each group, demonstrating that it is indeed only utilized when the bonobos are unwell.[15]

Monkeys

Tamarins were observed swallowing the large seeds of the fruit they regularly ingest. Although they are consumed along with the rest of the fruit, these seeds have no nutritional value for the monkeys. Since tamarins are routinely infected by trematodes, cestodes, nematodes, and acanthocephalans, there is speculation that the deliberate swallowing of these large seeds can help dislodge the parasites from the monkey's body.[16]

Bears

Similar to the wild chimpanzees,

Alaskan brown bears will swallow whole Carex leaves in the springtime to ensure the complete expulsion of parasites during their hibernation.[17]
Specifically, as tapeworms thrive off previously digested nutrients in the gut, the rough Carex leaves will lacerate their scolices, facilitating the defecation process. The proactive swallowing of these leaves will ensure low levels of active parasites within a hibernating bear.

Ingestion

Many examples of zoopharmacognosy involve an animal ingesting a substance with (potential) medicinal properties.

Birds

consuming clay in the Tambopata National Reserve, Peru

Many

gut.[18]

Great bustards eat blister beetles of the genus Meloe maybe to decrease parasite load in the digestive system;[19] cantharidin, the toxic compound in blister beetles, can kill a great bustard if too many beetles are ingested.[20] Great bustards may eat toxic blister beetles of the genus Meloe to increase the sexual arousal of males.[21] Some plants selected in the mating season showed in-vitro activity against laboratory models of parasites and pathogens.[22]

Invertebrates

tachinid flies. The caterpillars ingest plant toxins called pyrrolizidine alkaloids, which improve survival by conferring resistance against the flies. Crucially, parasitised caterpillars are more likely than non-parasitised caterpillars to specifically ingest large amounts of pyrrolizidine alkaloids, and excessive ingestion of these toxins reduces the survival of non-parasitised caterpillars. These three findings are all consistent with the adaptive plasticity theory.[6]

The

tobacco hornworm ingests nicotine which reduces colony growth and toxicity of Bacillus thuringiensis, leading to increased survival of the hornworm.[14]

Ants

Ants infected with Beauveria bassiana, a fungus, selectively consume harmful substances (reactive oxygen species, ROS) upon exposure to a fungal pathogen, yet avoid these in the absence of infection.[23]

Mammals

A variety of simian species have been observed to medicate themselves when ill using materials such as plants.
A conceptual representation of how pre- and post-ingestive events control the manifestation of self-medicative behavior in mammalian herbivores[24][clarification needed]

Great apes often consume plants that have no nutritional values but which have beneficial effects on gut acidity or combat intestinal parasitic infection.[1]

Chimpanzees sometimes select bitter leaves for chewing. Parasite infection drops noticeably after chimpanzees chew leaves of pith (Vernonia amygdalina), which contain sesquiterpene lactones and steroid glucosides that are particularly effective against schistosoma, plasmodium and Leishmania.[25] Specifically, these compounds can induce paralysis within the parasites and impair its ability to absorb nutrients, move, and reproduce.[26] Chimpanzees do not consume bitter on a regular basis, but when they do, it is often in small amounts by individuals that appear ill.[27] Jane Goodall witnessed chimpanzees eating particular bushes, apparently to make themselves vomit.[citation needed]

anti-microbial activity.[28]
Illustrating the medicinal knowledge of some species, apes have been observed selecting a particular part of a medicinal plant by taking off leaves and breaking the stem to suck out the juice.[29]

Anubis baboons (Papio anubis) and hamadryas baboons (Papio hamadryas) in Ethiopia use fruits and leaves of Balanites aegyptiaca to control schistosomiasis.[30] Its fruits contain diosgenin, a hormone precursor that presumably hinders the development of schistosomes.[4]

African elephants (Loxodonta africana) apparently self-medicate to induce labour by chewing on the leaves of a particular tree from the family Boraginaceae; Kenyan women brew a tea from this tree for the same purpose.[31]

White-nosed

ectoparasites such as fleas, ticks, and lice, as well as biting insects such as mosquitoes;[32] the resin contains triterpenes α- and β-amyrin, the eudesmane derivative β-selinene, and the sesquiterpene lactone 8β-hydroxyasterolide.[28]

Domestic cats and dogs often select and ingest plant material, apparently to induce vomiting.[33]

Indian wild boars selectively dig up and eat the roots of pigweed which humans use as an anthelmintic. Mexican folklore indicates that pigs eat pomegranate roots because they contain an alkaloid that is toxic to tapeworms.[34]

A study on

sodium bentonite, polyethylene glycol and dicalcium phosphate, respectively). Control lambs ate the same foods and medicines, but this was disassociated temporally so they did not recuperate from the illness. After the conditioning, lambs were fed grain or food with tannins or oxalates and then allowed to choose the three medicines. The treatment animals preferred to eat the specific compound known to rectify the state of malaise induced by the food previously ingested. However, control animals did not change their pattern of use of the medicines, irrespective of the food consumed before the choice.[35] Other ruminants learn to self-medicate against gastrointestinal parasites by increasing consumption of plant secondary compounds with antiparasitic actions.[24]

Standard laboratory cages prevent mice from performing several natural behaviours for which they are highly motivated. As a consequence,

autoimmune (MRL/lpr) mice readily consume solutions with cyclophosphamide, an immunosuppressive drug that prevents inflammatory damage to internal organs. However, further studies provided contradictory evidence.[1]

During the cold and rainy seasons, the crested porcupines (

endoparasites.[37]
During this time, it is observed that these porcupine populations actively sought out a rather large variety of medicinal plants, mostly with antiparasitic properties, to consume. When ingested, these plants appeared to be relieving the symptoms of the infections, such as inflammation.

Geophagy

Main article:
Geophagy

Many animals eat soil or clay, a behaviour known as

kaolin.[38] It has been proposed that for primates, there are four hypotheses relating to geophagy in alleviating gastrointestinal disorders or upsets:[39]

  1. soils adsorb toxins such as phenolics and secondary metabolites
  2. soil ingestion has an antacid action and adjusts the gut pH
  3. soils act as an antidiarrhoeal agent
  4. soils counteract the effects of endoparasites.

Furthermore, two hypotheses pertain to geophagy in supplementing minerals and elements:

  1. soils supplement nutrient-poor diets
  2. soils provide extra iron at high altitudes

colobus monkeys, mountain gorillas and chimpanzees seek out and eat clay, which absorbs intestinal bacteria and their toxins and alleviates stomach upset and diarrhoea.[40] Cattle eat clay-rich termite mound soil, which deactivates ingested pathogens or fruit toxins.[1]

Topical application

Some animals apply substances with medicinal properties to their skin. Again, this can be prophylactic or curative. In some cases, this is known as self-anointing.

Mammals

A female capuchin monkey in captivity was observed using tools covered in a sugar-based syrup to groom her wounds and those of her infant.[41][42]

North American

Navajo Indians are said to have learned to use this root medicinally from the bear for treating stomach aches and infections.[28][43][44]

A range of primates rub

psychoactive, the behavior may also be a form of recreational drug use in animals.[48][49]

anting. The capuchins often combine anting with urinating into their hands and mixing the ants with the urine.[50]

Callicebus oenanthes have been observed rubbing leaves of Piper aduncum on their furs and abdominal areas. Since these leaves contain insecticides like dillapiole and phenylpropanoids, it is speculated that this fur-rubbing is an indication of a preventative measure to ward off insects.[51] Additionally, another species of titi monkeys, Plecturocebus cupreus, were seen rubbing their furs with the leaves of Psychotria, whose compounds have antiviral, antifungal, and analgesic properties.[10]

Birds

More than 200 species of song birds wipe ants, a behaviour known as

anting.[14] Birds either grasp ants in their bill and wipe them vigorously along the spine of each feather
down to the base, or sometimes roll in ant hills twisting and turning so the ants crawl through their feathers. Birds most commonly use ants that spray formic acid. In laboratory tests, this acid is harmful to feather lice. Its vapour alone can kill them.

Some birds select nesting material rich in anti-microbial agents that may protect themselves and their young from harmful infestations or infections.

neem tree (Azadirachta indica) but change to quinine-rich leaves of the Krishnachua tree (Caesalpinia pulcherrima) during an outbreak of malaria; quinine controls the symptoms of malaria.[28][53]

Social zoopharmacognosy

Wood ants incorporate resin into their nest to inhibit the growth of microorganisms.

Zoopharmacognosy is not always exhibited in a way that benefits the individual. Sometimes the target of the medication is the group or the colony.

Wood ants (

Metarhizium anisopliae in laboratory conditions, indicating the resin collection is prophylactic rather than therapeutic.[55]

Honey bees also incorporate plant-produced resins into their nest architecture, which can reduce chronic elevation of an individual bee's immune response. When colonies of honey bees are challenged with the fungal parasite (Ascophaera apis), the bees increase their resin foraging. Additionally, colonies experimentally enriched with resin have decreased infection intensities of the fungus.[56]

Transgenerational zoopharmacognosy

monarch butterflies
lay their eggs on toxic plants to reduce parasite growth and disease in their offspring.

Zoopharmacognosy can be classified depending on the target of the medication. Some animals lay their eggs in such a way that their offspring are the target of the medication.

Adult monarch butterflies preferentially lay their eggs on toxic plants such as milkweed which reduce parasite growth and disease in their offspring caterpillars.[57] This has been termed transgenerational therapeutic medication.[58]

When detecting

endoparasitoid wasps, fruit flies (Drosophila melanogaster) lay their eggs in leaves with high ethanol content as a means of protection for their offspring.[59] These wasps, especially those of the Leptopilina genus, will inject their eggs in approximately 80% of fruit fly larvae.[60] As these wasp eggs develop, they will consume extensively through the larvae. To combat this, the fruit fly larvae will consume a large amount of ethanol from the food source to medicate themselves after wasp infection. Specifically, as the wasps are consuming more of the larvae, they will unknowingly consume more ethanol, which promptly leads to their deaths. This has been termed transgenerational prophylaxis.[58]

Value to humans

Main article: Herbal medicine

In an interview with Neil Campbell, Eloy Rodriguez describes the importance of biodiversity to medicine:

Some of the compounds we've identified by zoopharmacognosy kill parasitic worms, and some of these chemicals may be useful against

tumors. There is no question that the templates for most drugs are in the natural world.[29]

Media

See also

References

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Further reading

  • Samorini, Giorgio (2002) Animals and Psychedelics: The Natural World And The Instinct To Alter Consciousness
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