bios 5970: plant-herbivore interactionshomepages.wmich.edu/~malcolm/bios5970-plant-herbivore/... ·...
TRANSCRIPT
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm --- Week 2: Plant defenses and herbivore feeding Slide 1
BIOS 5970: PLANT-HERBIVORE INTERACTIONS
• B. PLANT DEFENSES AND HERBIVORE FEEDING • Week 2.
• 1. The world is green: • Darwin “noted that sheep of different breeds have
different susceptibilities to plant poisons.” • “It is no surprise to an evolutionary ecologist that insects
quickly evolve resistance to insecticides. Long evolutionary history has given insects the ability to detoxify a myriad of natural plant poisons, and the potential to evolve resistance to artificial toxins similar to those with which they can naturally cope.”
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm --- Week 2: Plant defenses and herbivore feeding Slide 2
2. Evolutionary trade-offs:
• Trade-off between defense and growth • For example:
• Allele differences at two loci determine whether clover (Trifolium repens) is cyanogenic and produces cyanide.
• Cyanogenic plants grow more slowly than acyanogenic plants
• But this cost is more than compensated for by effective defense against insect and snail herbivores.
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm --- Week 2: Plant defenses and herbivore feeding Slide 3
3a. Testing hypotheses to explain observations (patterns to processes): • Initial observation:
• Woodland ants carry seeds of violets (Fig. 1.1) and Dutchman's breeches (Fig. 2.1) - why?
• a) Comparative method: • Ants take seeds to nests (some eaten, some
survive). • Dicentra has seeds with nutrient-rich
elaiosomes. • Inconclusive.
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm --- Week 2: Plant defenses and herbivore feeding Slide 4
3b. Testing hypotheses to explain observations (patterns to processes): • b) Observation >> hypotheses:
• Initial observations plus library research suggested 3 alternative hypotheses:
• (i) Ants are seed predators. • (ii) Ants remove seeds for nutrient-rich elaiosomes
but are not effective dispersal agents. • (iii) Ants disperse seeds.
• Then see that ants keep Dicentra seeds in caches inside their nests.
• Seeds in ant nests are intact with elaiosomes chewed off. • However, ants abandon nests frequently.
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm --- Week 2: Plant defenses and herbivore feeding Slide 5
3c. Testing hypotheses to explain observations (patterns to processes): • c) Experimental method:
• Test whether seed survivorship (per capita) is higher for seeds taken by ants than seeds left alone.
• Need replicated and controlled experiments.
• Thus a combination of observational, comparative, and experimental evidence is most valuable to answer the original question.
• see Table 2-1 for the results of an experiment in which ants enhance seed survivorship during germination.
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm --- Week 2: Plant defenses and herbivore feeding Slide 6
4. Why is the Earth so green?
• Bottom-up (plant defense) versus top-down control (natural enemies).
• Adaptation and counteradaptation: • Plants use a variety of devices to protect roots,
stems, leaves, and seeds (flowers?). • For example:
• Cellulose roughage slows digestion. • Exotic amino acids interfere with protein formation.
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm --- Week 2: Plant defenses and herbivore feeding Slide 7
5. Herbivore counteradaptation to plant defenses:
• Herbivores counter-defend with ploys such as: • Behavioral avoidance.
• Digestive chemicals that dismantle lethal plant
molecules.
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm --- Week 2: Plant defenses and herbivore feeding Slide 8
6. Tactics versus strategies:
• Tactics can respond to particular interactions within strategic, evolutionary, phenotypic constraints.
• Strategies determine the operation range of various tactics. • Thus specialization is a feeding strategy, but
alkaloid detoxification is a tactic.
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm --- Week 2: Plant defenses and herbivore feeding Slide 9
7. Herbivory:
• Herbivory is not simply the consumption of plants by animals, it is a process that describes the interaction between plant defense and herbivore foraging (Fig.20.1 from Malcolm, 1992).
• 450 million years of evolution has produced huge diversity in both plants and herbivores.
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm --- Week 2: Plant defenses and herbivore feeding Slide 10
8. Interactions among 3 trophic levels:
• Tritrophic interactions: • Like herbivory,
predation is a process that describes the interaction between defense and foraging (Fig. 20.1: Malcolm, 1992)
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm --- Week 2: Plant defenses and herbivore feeding Slide 11
9a. Plant defenses:
• (1) Mechanical protection on the plant surface: • Includes spines, trichomes, glandular hairs (Fig. 3.2).
• (2) Complex polymers or silica crystals to reduce plant digestibility: • Digestibility Reducers (Table 3-1):
• Dose-dependent or quantitative, because the more that are present the less nutritional resource a herbivore receives.
• Includes cellulose, hemicellulose, and pectin as complex polysaccharides (Fig. 3-3) that can be 80-90% of plant dry weight.
• As well as lignins, tannins and silica.
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm --- Week 2: Plant defenses and herbivore feeding Slide 12
9b. Plant defenses:
• Omnivores & carnivores cannot digest nutrients in the presence of digestibility reducers.
• So many herbivores require symbiotic microbes associated with digestive modifications. • Also lignins (complex phenolic polymers) bind to
polysaccharides; waxes or cutins and tannins (also polyphenols but not bound to polysaccharides).
• Condensed tannins bind to protein and reduce digestion by: • (i) Blocking the action of digestive enzymes, or, • (ii) Binding to proteins being digested, or • (iii) Interfering with protein activity in the gut wall.
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm --- Week 2: Plant defenses and herbivore feeding Slide 13
9c. Plant defenses:
• (3) Toxins that kill or repel herbivores at low concentrations:
• Secondary compounds with a defensive rather than a metabolic function
• Secondary metabolites or allelochemicals (see Fig. 3-4 for metabolic sources).
• Qualitative toxins are poisonous and are very diverse (Table 3-1 and Fig. 3-5).
• Include alkaloids, terpenoids and HCN (Fig. 3-6 common in almonds and cherries etc.) which blocks cytochrome oxidase and hence cellular respiration.
• See Table 9-2 for evolution of toxic chemicals in plants.
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm --- Week 2: Plant defenses and herbivore feeding Slide 14
10. Constitutive versus Inducible defenses
• Constitutive: • Permanent protection always present:
• e.g. spines and trichomes as well as many chemicals that reduce digestibility and also function as structural support.
• They could also include some toxins.
• Inducible: • Responses by individual plants to tissue damage:
• e.g. very widespread proteinase inhibitors: • Polypeptides and proteins that block catalytic activity of proteolytic
enzymes by binding to the active site of the enzyme molecule.
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm --- Week 2: Plant defenses and herbivore feeding Slide 15
11. Herbivore Foraging:
• Scale: size range from aphids to elephants! • Dan Janzen: “the plant world is not colored green;
it is colored morphine, caffeine, tannin, phenol, terpene, canavanine, latex, phytohemagglutinin, oxalic acid, saponin, and L-dopa.” • Sensory modality for signal reception. • “Why do different herbivores eat different
plants?” (page 40). • Herbivores have mechanical, biochemical,
physiological, and behavioral countermeasures to plant defenses (Table 3-2).
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm --- Week 2: Plant defenses and herbivore feeding Slide 16
12. Mechanical breakdown of plant food
• To break open cells: • Mammals use teeth:
• low-crowned and high-crowned (Figs. 3-8 & 9-8).
• Birds use beaks (cardinal) or gravel-filled gizzards (turkey, dodo).
• Insects use chewing or sucking mouthparts (Fig. 3-9).
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm --- Week 2: Plant defenses and herbivore feeding Slide 17
13. Microbial symbionts
• Many herbivores have bacteria, flagellates and protozoans that can synthesize necessary vitamins, break down plant material, and detoxify allelochemicals through anaerobic fermentation.
• Structural modifications to the gut: • Foregut (sheep) and hindgut (horse) fermentors
(Table 3-3). • Ruminants (Fig 3-10):
• 4-chambered stomach: rumen (+reticulum), omasum, and abomasum.
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm --- Week 2: Plant defenses and herbivore feeding Slide 18
14. Herbivore gut ecosystems:
• 1 ml of sheep rumen fluid includes: • 16,100 x 106 bacteria, 106 flagellates and 3.3 x 105
ciliated protozoans. • Whole sheep rumen holds 6L ! • Digestion efficiency (Table 3-4):
• Depends on volume, retention time and proportion of indigestible material in plant food.
• Larger herbivores (bison at 450-1,350 kg take 80 hours to process fiber at about 70% efficiency) hold food longer than smaller herbivores.
• White-tailed deer at 48-100 kg take 45 hours to process food at 56% efficiency.
• Humans at 60 kg digest only 9% of alfalfa fiber eaten.
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm --- Week 2: Plant defenses and herbivore feeding Slide 19
15. Figure 3-12: Digestibilities of different forages to mule deer.
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm --- Week 2: Plant defenses and herbivore feeding Slide 20
16. Insect herbivores:
• Cannot use large gut volumes and high retention times, so they specialize more and have a variety of ways to use symbiotic microbes (Table 3-5).
• Insects often have: • Long guts or elaborate cecae (Fig. 3-13), or, • Intracellular symbionts in mycetocytes together as
mycetomes (Fig. 3-14), or, • Fungal symbionts that are cultivated outside their bodies
(like leaf cutter ants and bark beetles).
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm --- Week 2: Plant defenses and herbivore feeding Slide 21
17. Digestive enzymes:
• Both general and specific enzyme systems are used.
• The best known are: • Mixed-function oxidases (MFOs).
• These are membrane-bound enzymes that detoxify a wide range of poisons.
• Vertebrates: • Highest activity in the microsomes of the endoplasmic
reticulum of liver cells.
• Insects: • Mostly in fat bodies or midgut.
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm --- Week 2: Plant defenses and herbivore feeding Slide 22
18. Characteristics of MFO systems:
• (1) Catalyze oxidative reactions. • (2) Nonspecific. • (3) Easily induced by exposure to novel toxins.
• They detoxify (Fig. 3-15) by: • (1) Primary degradation to make water soluble
• e.g. adding hydroxyl (-OH) groups) • (2) Conjugation with sugars, amino acids, sulfates, phosphates, or
other molecules headed for excretion. • This makes toxins soluble and excretable. • There is generally more MFO activity in insects with
broader diets than those with narrower diets and generalists are better adapted for degrading novel toxins.
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm --- Week 2: Plant defenses and herbivore feeding Slide 23
19. Choice and Avoidance:
• Diet breadth spectrum: • Polyphagous - many food species • Oligophagous - few food species • Monophagous - single food species
• Variable diet breadth poses different sets of problems: • Most mammals have to be polyphagous, or at
least oligophagous, because they are large. • But most insects are small and less mobile and
need to be oligophagous or monophagous.
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm --- Week 2: Plant defenses and herbivore feeding Slide 24
Figure 1.1: Formica podzolica ant holding violet seed by its elaiosome
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm --- Week 2: Plant defenses and herbivore feeding Slide 25
Figure 2.1: Flowers of Dutchman’s breeches (Dicentra cucullaria) and seed with elaiosome
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm --- Week 2: Plant defenses and herbivore feeding Slide 26
Table 2.1: Seedling emergence of violets in different treatments
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm --- Week 2: Plant defenses and herbivore feeding Slide 27
Figure 3.2:
External protection of plants: (a) cactus spines; (b) hooked bean trichomes; (c) potato glandular hairs
a
bc
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm --- Week 2: Plant defenses and herbivore feeding Slide 28
Table 3.1:
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm --- Week 2: Plant defenses and herbivore feeding Slide 29
Figure 3.3:
Digestibility reducers in plants.
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm --- Week 2: Plant defenses and herbivore feeding Slide 30
Figure 3.4: Biosynthetic origins of primary and secondary plant products
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm --- Week 2: Plant defenses and herbivore feeding Slide 31
Figure 3.5:
Some toxic secondary compounds in plants: caffeine from coffee beans (Coffea), strychnine from Strychnos fruits, and the terpenes, pyrethrin from Chrysanthemum and glaucolide A from a sunflower.
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm --- Week 2: Plant defenses and herbivore feeding Slide 32
Figure 3.6: Cyanide production by damaged cherry leaves (Prunus).
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm --- Week 2: Plant defenses and herbivore feeding Slide 33
Table 9.2:
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm --- Week 2: Plant defenses and herbivore feeding Slide 34
Table 3.2:
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm --- Week 2: Plant defenses and herbivore feeding Slide 35
Figure 3.8: Low crowned tooth of omnivorous browsing mammal and high-crowned tooth of grazing mammal
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm --- Week 2: Plant defenses and herbivore feeding Slide 36
Figure 9.8: Diversity of grazing and browsing Miocene horse genera of North America.
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm --- Week 2: Plant defenses and herbivore feeding Slide 37
Figure 3.9: Insect mouthparts (a) chewing grasshopper, (b) seed-sucking milkweed bug.
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm --- Week 2: Plant defenses and herbivore feeding Slide 38
Table 3.3:
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm --- Week 2: Plant defenses and herbivore feeding Slide 39
Figure 3.10: Mammalian digestive tracts: fore & hind-gut fermentors and a carnivore
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm --- Week 2: Plant defenses and herbivore feeding Slide 40
Table 3.4:
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm --- Week 2: Plant defenses and herbivore feeding Slide 41
Table 3.5:
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm --- Week 2: Plant defenses and herbivore feeding Slide 42
Figure 3.13: Grasshopper gut with expanded volumes and ceca for microflora
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm --- Week 2: Plant defenses and herbivore feeding Slide 43
Figure 3.14: Mycetocytes in the midgut of a chrysomelid beetle
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm --- Week 2: Plant defenses and herbivore feeding Slide 44
Figure 3.15: Mixed function oxidase (MFO) degradations of toxins: (a) hydrolysis of DDT, (b) N-oxidation of nicotine.