Читать книгу Recent Advances in Polyphenol Research - Группа авторов - Страница 48

An evolutionary relationship between plants and mammals has conditioned the unique physiological/biomedical effects of wild plants (Wynn and Fougere 2007). Traditional ecological knowledge (as held in indigenous tribal communities) asserts that at least some animals instinctively know how to treat their own injuries or ills and self‐medicate using herbs growing in the wild. Consequently, traditional herbalists routinely use judicious observations of the behavior of sick or distressed wild animals to locate new potential human remedies derived from wild plants (Engel 2007; Wynn and Fougere 2007). Native Americans, as well as tribal groups throughout the world, have observed animal feeding behavior and used these clues to guide their own use of polyphenol‐rich plants as medicines for specific ailments. For animals, is it assumed that nutritional wisdom or use of plant resources for healing is a combination of post‐ingestive hedonic feedback and individual learning. Animals can use hedonic feedback to find ways of removing the unpleasant sensations of disease and injury. Some research has asserted that there is a purgative effect on the animal’s intestines that helps alleviate parasitic infections (see details below), whereas other theories maintain that the natural antimicrobial/wound‐healing effects provided by plant polyphenols are impetus for a wild animal’s tendency to seek berries or other polyphenolic resources, especially after they’ve incurred defensive wounds.

Zoopharmacognosy is defined as the use of plant medicines/medicinally active herbs by animals—specifically when an animal seeks out a plant that is not normally part of its diet (and may have no nutritive value) in order to cure injury or disease (Moerman 1996). Mammals and even birds and insects are able to self‐medicate using plant resources for both physical and psychological treatments. Native Americans revered the bear as one of the most advanced animals in terms of self‐medication, as they use their clawed paws to dig for medicinal root crops (Densmore 1974).

Native American traditional ecological knowledge observed that animals tend to “self‐regulate” tannin content via the diet (Moerman 1996; Engel 2007). Feeding deterrents (like tannins) are deliberately sought out by animals when the bioactive benefits outweigh the adverse tastes. For example, wild deer deliberately select plants not with very low tannin content, but those with moderate tannin content, as an adaptive taste preference, presumably because of the impact of the tannins on intestinal parasites. Repeated evidence suggests that animals attempt to self‐regulate tannin consumption to optimal levels. Similarly, the Asiatic two‐horned rhinoceros periodically will consume copious amounts of mangrove bark (tannin‐rich) to the point where their urine turns orange, to self‐medicate against endemic dysentery, just as a common medication for human dysentery (clioquinol) has a 50% tannin content (Engel 2007). During the coevolution of plants and animals, animals developed receptors for plant‐produced bioactive chemicals (benzodiazepine, opioid, and vanilloid), which had direct effects on the sensations of pain or of consciousness; the animal‐to‐plant relationships provided a template by which herbalists could treat human patients for seizures, anxiety, and pain.

Natural selection has streamlined a variety of animal behavioral health maintenance strategies. These innate behavioral strategies are well documented for wild animals and although the capacity is partially lost in domesticated animals, the latter have also been observed to self‐medicate. It has been noted that Native Americans who depended on their domesticated animals and observed their behaviors (e.g. Plains tribes and horses) had greater knowledge of plant medicine than other tribes (Stowe 1976). Farmers in New Zealand have noted that when captive deer grazed on forage containing tannin‐rich plants such as chicory, there was significantly less need to administer chemical de‐wormer. Parasitized deer and lambs selectively choose bitter and astringent chicory, which reduces their parasite loads. Consumption of condensed tannins increases sheep lactation, wool growth, and live weight gain by reducing the burden of internal parasites (Wynn and Fougere 2007).

Enthusiastic consumption of other polyphenol‐rich plants, including wild berries, is a typical behavior for dogs (Sueda et al. 2008). Anecdotal evidence suggests that dogs will mimic humans when foraging for berries and harvesting from gardens. Dogs apparently love all types of berries—blueberries, strawberries, blackberries, and raspberries have all been scavenged, often to the chagrin of their owners, as well as peas, fallen apples, and corn on the cob from gardens. Sled dogs routinely accompany their owners during wild berry harvesting in Alaska, as a safeguard to keep foraging bears at bay, and these dogs routinely scavenge the berries from the lower branches in a berry stand. In a formal study on the antioxidant status of sled dogs fed wild blueberries, berries were initially mixed into the kibble and fed to the treated animals; however, it soon became apparent that the dogs preferred the berries and if placed on top of the kibble, they’d eat the berries first (Dunlap et al. 2006).

While it has been suggested that domesticated dogs are more omnivorous than wild animals, scat analysis has shown that wolves consume plants as well (Engel 2007) (Figure 3.1). As facultative carnivores, dogs and wolves do not have a physiological requirement for plant carbohydrates, but plants in the canine diet can play a role in health maintenance. Fruits are a vitamin and mineral source for the animals as well as a fiber source. While canines lack salivary amylase (to break down plant carbohydrates) they do produce the enzyme through the pancreas and small intestine. Scat analysis and anecdotal observations of hunters and trappers indicate that fox, coyote, moose, and wolf typically have plant fiber hulls and berry seeds/skins in their feces. Fiber, both soluble and insoluble, may be a primary benefit to the animal of plant consumption, and is an important additive in commercial companion‐animal feed. Plant‐eating behavior is coincident with meat consumption, and does not occur only in the absence of animal prey.

Figure 3.1 Wild wolf feeding on Alaskan salmonberries.

Source: Illustration by Ginger Dunlap.

Grizzly and black bears in Alaska are also notorious for copious consumption of wild berries, necessitating that Alaska Native and aboriginal Canadian berry harvesters must carry firearms for protection (as well as their domesticated sled dogs). Hunters have reported that during berry ripening season, grizzly bears actually have blue coloration from the berries interlaced in their fat deposits, and the meat acquires a sweeter flavor (Dr. Arleigh J. Reynold, DVM, PhD, University of Alaska Fairbanks, 2018, personal communication, 10 August).

Nonhuman primates frequently make use of plants and other natural resources to self‐medicate. The most frequent observations are ingestion of natural products to purge intestinal parasites. Chimpanzees in Tanzania have been observed to fold, and then swallow, whole Aspilia spp. leaves without mastication; there is no known nutritional value but the undigested rough textured leaves help to expel parasitic worms into the feces. Similar cases where monkeys have ingested certain plants to dislodge parasites have been recorded. Primate behavior of this kind has helped to guide scientists to previously unscreened plant material that may have antimicrobial or antiparasitic properties. One very intriguing recent discovery with primates involves lemurs in Madagascar who deliberately chew on and vigorously rub millipedes, causing them to release secreted toxins in defense. Only then, once the toxins containing benzoquinones are released, the lemurs eat the crushed insects and rub them on their genitalia in order to kill parasitic worms (Bittel 2018).