Neotropical Pharmacy

1. Neotropical Pharmacy • Very few leaves have insect damage. Why? • Blackrivers are black. Why? • Leaves are constantly exposed to dangers, whatever the source

2. Neotropical Pharmacy • In one study, it was estimated that the Amazon rainforest produced 900 metric tons per ha. • The mass of all animals was estimated to be a mere 0.2 ha (0.02% of plant biomass)

3. Neotropical Pharmacy • Very few secondary consumers (herbivores - 7%) • Compare this to 19% eating living or dead wood (termites) • 50% ate only dead vegetation • 24% some sort of carnivore • Why so few herbivores??

4. Neotropical Pharmacyplant defense compounds • Drugs, drugs, drugs • Leaves of both tropical and temperate zone plants are abundantly full of noxious chemicals • “the world is not colored green to the herbivore’s eyes, but rather is painted morphine, L-DOPA, calcium oxalate, cannabinol, caffeine, mustard oil, strychnine, rotenone, etc” Janzen

5. Neotropical Pharmacyplant defense compounds • Most of these chemicals are termed ‘secondary compounds’ because most seem to lack a direct metabolic function, such as those in photosynthesis (also called allelochemics for defense at large)

6. Neotropical Pharmacyplant defense compounds • Their origin may have been by chance, with each combination potentially providing a little better defense • As a result, most plants don’t just have a single compound…Why? • Most have several, primarily to protect against herbivores, bacteria and/or fungi

7. Neotropical Pharmacyplant defense compounds • Alkaloids are among the most familiar and addictive drugs known • Such drugs as cocaine (from coca), morphine (opium poppy), cannabidiol (hemp), caffeine (teas and coffees), and nicotine (tobacco) There are over 4,000 known alkaloids from >300 families and >7,500 sp • About 20% of temperate sp contain them

8. Neotropical Pharmacyplant defense compounds • Alkaloids have a bitter taste (to mammals) and tend to disrupt liver and cell membrane function • May also cause cessation of lactation, abortion, or birth defects • Clearly many are addictive!!

9. Neotropical Pharmacyplant defense compounds • For example, caffeine has been shown to discourage insect feeding • So is it a stimulant to us, an insecticide!

10. Neotropical Pharmacyplant defense compounds • Phenolic compounds are often abundant in plants • One group adds the pungency to many of well-known spices and tannins provide the basic compounds used in tanning leather • Particularly abundant in oaks and mangroves

11. Neotropical Pharmacyplant defense compounds • Work on Cecropia indicate young trees have high levels but older plants have less • Plants in shade had less…so what? • In field experiments, plants with low levels suffered 2x the herbivory • More leaves, less toxin per leaf…so what

12. Neotropical Pharmacyplant defense compounds • Phenolics are small proteins stored in cell vacuoles that are broken when an insect or other herbivore bites the leaf • Upon release, the phenols combine with various proteins, including those enzymes necessary for splitting polypeptides (parts of proteins) in digestion, perhaps making it more difficult for a herbivore to digest protein

13. Neotropical Pharmacy plant defense compounds • It is thought leaf damage by insects or pathogens may stimulate production of phenolics • However, not all insects are bothered by these compounds (e.g. leafcutting ants) • They may be more valuable against microbes and/or pathogens

14. Neotropical Pharmacy plant defense compounds • Saponins are soaplike compounds that are relatively common in tropical plants and act to destroy the fatty component of the cell membrane. Some indigenous people utilize saponins to poison and capture fish, interfering with respiration

15. Neotropical Pharmacy plant defense compounds • Cyanogenic Glycosides (cyanide + sugar) • When the sugar is digested, the sugar is released leaving the hydrogen cyanide • Consequently, these plants are avoided by many species of herbivore

16. Neotropical Pharmacy plant defense compounds • Passionflowers, fed upon by caterpillars of Heliconius butterflies, have a relatively high load • Each species can detoxify one or two cyanogenic glycosides, and thus specialize on these species

17. Neotropical Pharmacy plant defense compounds • Some strains of manioc have high concentrations of cyanogenic glycoside in the root • To eat this, root must be washed thoroughly

18. Neotropical Pharmacy plant defense compounds • Cardiac Glycosides interfere with heart function. Digitalis, from the temperate zone plant foxglove and members of the milkweed family

19. Neotropical Pharmacy plant defense compounds • Terpenoids area a complex group of fat-soluble compounds that include monoterpenoids, diterpenoids, and sesquiterpenoids. Some are used in the synthesis of compounds that may mimic insect growth hormones or can be modified into cardiac glycosides • Some discourage both insects and fungi (especially those that ants culture)

20. Neotropical Pharmacy plant defense compounds • Toxic Amino Acids are common in the bean and pea families and interfere with normal protein synthesis • Some are strong hallucinogens (e.g. L_DOPA)

21. Neotropical Pharmacy plant defense compounds • Among the most familiar tropical plants are philodendrons in the arm family • In the US, we have skunk cabbage, and these plants contain crystals of Calcium Oxalate, a caustic substance that makes the delicate tissues of the mouth burn

22. Neotropical Pharmacyother defenses • Latex is another form of defense • For those species who have developed chemical defense, adhesion to mouth parts is a strong defense

23. Neotropical Pharmacyother defenses • Other species may be spiny or thorny or have leaves coated with diminutive ‘bed of nails’ called trichomes that sometimes impale caterpillars • Even serrated leaves can be an effective deterrent for some predators

24. Neotropical Pharmacyother defenses • Leaf toughness, nutrition value and fiber content also affect ability to resist herbivores • In general, young leaves are eaten more than older leaves, even when phenols were present suggesting other factors could be quite influential

25. Neotropical PharmacyLatitudinal Trends • Levin (1976) made a detailed study of the geographic distribution of alkaloid-containing plants • Groups of herb, shrub, and tree species each contained a significantly greater percentage of tropical species with alkaloids (27%-45%)

26. Neotropical PharmacyEcological Trends • Although defense compounds occur in species that occupy virtually all habitats, there are some trends • Tropical lowland forests, mangrove swamps, deserts, and mountain rain and cloud forests are all habitats where defense compounds are abundant • Alpine forests and grasslands, as well as disturbed areas have few such plants

27. Neotropical PharmacyEcological Trends • Defense compounds are abundant in lowland forest occurring on nutrient poor white, sandy soil forests, in the northern Amazon • Replacing leaves are expensive and consequently, are long-lived and have extremely high concentrations of defense compounds

28. Neotropical PharmacyEcological Trends • Ultimately, leaves must be leached of compounds so they can be broken down • What else do we find associated with this area?

29. Neotropical PharmacyEcological Trends • Areas undergoing ecological successin tend to have species that invest in defense compounds differently from those on poor soil • Most successional species are racing to maximize their rates of growth • They synthesize phenolics, cyanogenics and alkaloids, albeit in low concentrations, suggesting a low energy cost to do so

30. Neotropical PharmacyEcological Trends • Contrasting strategies may simply reflect the resource availability • E.g. on sites where are poor, “expensive”, long lasting defense compounds are favored and on rich sites, “cheaper”, shorter-lived defense compounds are favored because the tree is able both to devote sufficient energy to rapid growth and replace defense compounds as needed

31. Neotropical PharmacyEcological Trends • As a result, many early-successional species are subject to herbivore damage. • Janzen has estimated insect density may be 5-10x higher in successional areas

32. Neotropical PharmacyPlants vs. Monkeys • Most monkeys are vegetarians • However, they are surrounded by beautiful leaves, only of which a small subset are palatable

33. Neotropical PharmacyPlants vs. Monkeys • The serendipitous adventure of Kenneth Glander • He saw a mantled howler monkey fall 10m from a tree • What would your thoughts be?

34. Neotropical PharmacyPlants vs. Monkeys • She was eating from the madera negra tree, which local use to obtain rotenone • He spent 5,000 hrs watching howlers and maked 1,699 trees to see what they were eating

35. Neotropical PharmacyPlants vs. Monkeys • Not surprisingly, monkeys are extremely selective in their feeding • Of the 149 madera negra trees in the study area, the troop only fed on 3 trees! • Not surprisingly, these three trees were found to have leaves free of alkaloids and cardiac glycosides, which are normally very high in this species

36. Neotropical PharmacyPlants vs. Monkeys • Glander found that mantled howlers tended to favor young leaves that are relatively high in nutritional value but have not yet become loaded with defense compounds • But when given little choice, they eat a few mature leaves and move to another tree. Why?

37. Neotropical PharmacyPlants vs. Monkeys • Milton, studying on BCI, suggested that it was the relative amounts of protein ad fiber content, not secondary compounds • These individuals tended to favor leaves that had a higher protein to fiber ratio

38. Neotropical PharmacyPlants vs. Insects • How do those little herbivorous insects cope with all the compounds?? • One approach is to become highly specialized on just a few kinds of plants • Being so small, most insects, including temperate species, can afford to become dietary specialists

39. Neotropical PharmacyPlants vs. Insects • E.g. heliconius caterpillars feed exclusively on the vines of passionflowers • The author discusses the complete defoliation of a single tree while all surrounding plants remained untouched

40. Neotropical PharmacyPlants vs. Insects • Imagine if an insect were able to detoxify defense compounds (or sequester them), they could focus on that particular species and do quite well • Also, if other species can’t detoxify the species in question, you may have a potential monopoly on this species

41. Neotropical PharmacyPlants vs. Insects • Of course, there are generalists as well • How do these guys get away with being generalists?

42. Neotropical PharmacyPlants vs. Insects • Brachid Beetles provide examples of both feeding specialization and adaptation to host defenses • Bruchids are seed predators, especially on legumes • Females lay eggs on seed pods or directly in seeds and larvae enter pods upon hatching and feed on seeds before pupating

43. Neotropical PharmacyPlants vs. Insects • In a survey of Bruchidae, Curclionidae, and Cerambycidae, about 75% of the species fed on a single plant species • Only about 12% fed on 3 or more sp • Bruchids are widespread and encounter a variety of potential hosts • However, there are local races adapted to a particular species

44. Neotropical PharmacyPlants vs. Insects • Consider the Arms race with Bruchids • Some hosts evolve toxic seeds, bruchids either avoid them or become resistent • Some seed pods produce sticky gum following penetration of bruchid larvae • Bruchids arrest development until seeds mature and it is too late for pods to produce gum

45. Neotropical PharmacyPlants vs. Insects • Some seed pods flake, removing eggs • Bruchids oviposit beneath the flaking • Some pods fragment or explode • Bruchids oviposit directly on the seed • Some seeds remain very small, then grow quickly just prior to dispersal • Bruchids enter and eat immature seeds or delay development, eating the bigger, mature seeds

46. Neotropical PharmacyPlants vs. Insects • Both temperate and tropical butterflies are known for their affinities for feeding on specific plant families • Caterpillars are usually much more selective than adults, who are feeding on nectar and aiding in pollen dispersal • Furthermore, adults and juveniles have very different relationships with plants

47. Neotropical PharmacyPlants vs. Insects • Heliconid Butterflies and Passionflowers • A relatively exclusive relationship • Passionflowers contain various cyanogenic glycosides and cyanohydrins, probably a response to strong herbivory by heliconids • In addition, many species of passionflower have recruited ants

48. Neotropical PharmacyPlants vs. Insects • Additional adaptations…

49. Neotropical PharmacyPlants vs. Insects • One species of passionflower is winning as it is covered by minute hooked spines called trichomes • As a result, caterpillars become impaled • What should they do? • E.g. Mechantis isthmia and tomatoes

50. Neotropical PharmacyEthnobotany & Ethnozoology • Native peoples (locals) in te tropics have much experience dealing with some of the toxins of the tropics • Consider manioc; it grows well in poor soil, but also concentrates defenses like other plants growing in poor soils (specifically cyanogenic glycosides) • Must grate it, soak it, and dry it