BIOL 4120: Principles of Ecology Lecture 14: Parasitism and Mutualism

1. BIOL 4120: Principles of Ecology Lecture 14: Parasitism and Mutualism Dafeng Hui Room: Harned Hall 320 Phone: 963-5777 Email: dhui@tnstate.edu

2. Outline (chapter 15) 15.1 Parasite draw resources from host organisms 15.2 Hosts provide diverse habitats for parasites 15.3 Direct transmission between host organisms 15.4 Multiple hosts and stages 15.5 Hosts respond to parasitic invasions 15.6 Parasite can impact host survival and reproduction 15.7 Parasites may regulate host population 15.8 Parasites can evolve into a positive relationship 15.9 Symbiotic mutualisms are involved in the transfer of nutrients 15.10 Some symbiotic mutualisms are defensive 15.11 Mutualisms may be nonsymbiotic 15.12 Mutualisms are often necessary for pollination, seed dispersal 15.13 Mutualism can influence population dynamics 15.14 A simple model

3. Parasitism: a relationship of two organisms living together (symbiosis) and one derives its nourishment at the expense of the other Parasite and host Parasitism has Negative effect on hosts But do not usually kill hosts Parasite consists of a wide range of organisms, including Virus, bacteria, protists, fungi, plants, and invertebrates (include arthropods) 15.1 Parasites draw resources from host organisms

4. According to size, parasites may be classified as Microparasites Small size and short generation time Viruses, bacteria, fungi, protozoa etc May cause disease Usually direct transmission from host to host: Air, water, etc Macroparastites Relatively large, have comparatively long generation time Liver flukes, lice, ticks, mistletoe (shrub), etc Do not complete an entire life history in one host, usually more than one host Both direct and indirect transmission, later involves a vector such as a mosquito for malaria Parasites draw resources from host organisms

5. Hosts are the habitats for parasites Depends on the places: Ectoparasites: live on the skin within the protective cover of feathers and hair Endoparasites: live within the host Examples: Fleas, ticks, are ectoparasites Live flukes, lung flukes, flatworms, are endoparasites 15.2 Hosts provide diverse habitats for parasites

6. Animal host: Ectoparasites: live on the legs, on the upper and lower body surfaces, and even on the mouthparts Endoparasites: live in the bloodstream, heart, brain, digestive tract, nasal tracts, lungs, gonads, bladder, pancreas, eyes, gills of fish, muscle tissue, or other sites Plant host: Ecotparasites: live on the roots and stems, flowers, pollen or fruit Endoparasites: penetrate the roots, bark to live in the woody tissue beneath, within leaves. For parasites to survive and multiply, parasites have to escape (when a host dies) and infect another host Process of transmission from one host to another can occur by either direct or indirect means and can involve adaptations by parasites to virtually all aspects of feeding, social and mating behaviors in host species. Hosts provide diverse habitats for parasites

7. Direct Transmission From host to host, no intermediate organism involved Most mircoparasites are transmitted directly Two approaches: Direct contact with a carrier (host) Smallpox virus and the variety of bacterial and viral parasites associated with sexually transmitted diseases (HIV) Indirect through the air, water, or other substrate Influenza (airborne) SARS (bird flu) 15.3 Direct transmission can occur between host organisms

8. Macroparasites of animal and plants can move from infected hosts to uninfected hosts by direct transmission Animals Ectoparasites Fleas, ticks on birds and mammals Endoparasites Roundworms in mammals (life cycle in textbook, page 313) Plants Holoparasites and hemiparasite squawroot (parasitizes the roots of oaks) and beechdrops (parasitizes the root of beech trees) Direct transmission can occur between host organisms

9. Host  vector (intermediate organism)  host Animal black-legged tick Lyme disease (major arthropod-borne disease in US) Caused by bacteria, Borrelia burgdorferi It lives in the blood-stream of vertebrates, from birds to deer and humans Depends on tick for transmission from one host to another. Mosquito Malaria (still kills 0.7 to 2.7 million people in Africa) Caused by 4 species of protozoan parasites (Plasmodium) Blood-stream Infected female mosquitoes 15.4 Indirect transmission involves an intermediate vector

10. Plant Elm bark beetles Fungi Cause devastating Dutch elm disease from tree to tree Birds (through seed dispersal) Mistletoes (Phoradendron spp.) Hemiparasites (can do photosynthesis, but draw water and nutrients from host) Birds feed on the mistletoe fruits, seeds pass through digestive system, are deposited on trees. Sticky seeds attach to limbs and send out rootlets that embrace the limb and enter the sapwood. Indirect transmission involves an intermediate vector

11. Birds and mistletoe

12. Life history of an organism involves several stages Growth and reproduction or juvenile (prereproduction), reproduction, and postreproduction Some parasites can’t complete their entire life cycle in a single host species Definitive host: host species in which the parasite becomes an adult and reaches maturity (where adults reproduce) Intermediate host: other hosts which harbor some developmental phase of parasites (where juveniles grow) Intermediate hosts can be one, two or even three 15.5 Transmission can involve multiple hosts and stages

13. Transmission can involve multiple hosts and stages Deer picked infected snails. In stomach, larvae leave the snail, enter abdominal membranes, travel via spinal cord to brain. Mate and lay eggs, larvae and eggs pass through the bloodstream to lung, cough, swallow, and passed out through feces. Picked up by snails. The life history of a macroparasite, the meningeal worm Parelaphostrongylus tenuis. White-tailed deer, moose, and elk. Transmission is indirect, involving snails as intermediate host.

14. Adaptations of host species to minimize the impact of parasite Reduce parasitic invasion Combat parasitic infection once it has occurred Host response to parasite Avoidance Birds and mammals, grooming Birds, preening Deer seek dense and shaded places to avoid deerflies Inflammatory response in animals Stimulate secretion of histamines (chemical alarm signals), induce increased blood flow to site, resulting inflammatory Gall formation in plants Abnormal growth structure Cut off contact of fungus with health tissue 15.6 Host respond to parasitic invasions

15. Host response to parasite (cont.) Avoidance Inflammatory response in animals Gall formation in plants Immune response in animals When a foreign object such as a virus and bacteria (antigen), enter bloodstream, elicits an immune response White cells produce antibodies Antibodies target antigens present on the parasite’s surface, helping to counter their effect Host respond to parasitic invasions

16. Immune response in animals Antibodies expensive to produce Immune system has a remarkable “memory” Vaccination Sometimes, immune system does not work HIV and AIDS as an example HIV (human immunodeficiency virus), the causal agent of AIDS Transmitted sexually or through the use of shared needle, or by infected donor blood. Host respond to parasitic invasions

17. 15.7 Parasites affect host survival and reproduction • Parasites affect host survival and reproduction • Malaria in humans • Malaria on western fence lizard • Clutch size is 20% smaller • Can also reduce reproductive success of males • Secondary sex characteristics such as bright and ornate plumage of male birds • Infection influence the attraction • Parasites can increase mortality that can result from indirect consequences of infection

18. Infection of the California killfish

19. Parasites can be major regulators of population Plants Chestnut blight, nearly exterminated the American chestnut Dutch elm disease, nearly removed American elm from North America Humans Black Death in14th century Smallpox in 18th century Cholera in 19th century 15.7 Parasites may regulate host populations Parasites may act as a selective agent of mortality, infecting only a subset of the population.

20. Parasites may regulate host populations • Black Death in14th century • Needs lots of rats and some concentration of human population • Not a major problem to Romans or Chinese civilizations due to good urban planning • Smallpox in 18th century • Needs even high human population due to direct transmission • Halted by human evolution • Vaccination • Cholera in 19th century • Needs even higher density and water/food transmitted • Halted by human evolution • Clean water supply and bacteriology • AIDS in 21st century • Needs even higher population density • Never a problem in low density central African origin except to some villages • Sexual transmission requires large number of contact, cf syphilis in 19th century • Major effect on population once infection rate reaches 2%-5% • Exponential growth in southern Africa • Affects human productivity directly • Halted by • Change in human behavior? • Science?

21. Parasitism: Parasites gain benefits from hosts; hosts suffer. Commensalism: A relationship between two species in which one species benefits without significantly affecting the other Mutualism: A relationship between members of two species that benefit both. Individuals of both species enhance their survival, growth, or reproduction 15.9 Parasitism can evolve into a positive relationship

22. Commensalism • Defined as an ecological relationship in which one species benefits from other species, which is itself not affected one way or the other by the relationship • This is thus a “+, 0” relationship • Example: Spanish moss (epiphyte) on trees

23. Commensalism between cattle (as food beaters) and cattle egrets (three white birds, one sitting on cow) in Jamaica

24. Mutualism • Mutualism: Interactions between individuals of different species that benefit both partners. • Facultative Mutualism occurs when a species can live without its mutualistic partner. • Obligate Mutualism occurs when a species is dependent on a mutualistic relationship. • Lichens: symbiotic association • A fungus and an alga combined to form a spongy body (thallus).

25. Mutualism: Individuals of both species enhance their survival, growth, or reproduction can be symbiotic or nonsymbiotic At least one member of the pair becomes totally dependent on the other

26. Mutualism – more examples • Plants and pollinators • Plant and mycorrhizal fungi • Ash tree and mycorrhizal fungi • Corals and zooxanthellae • Phainopepla and mistletoe

27. Herbivores: Digestion system of cow Chamber of ruminant’s stomach contain large populations of bacteria and protozoa that carry out the process of fermentation. Anaerobic process Plants: Nitrogen fixation N-fixing bacteria: Rhizobium Legumes: clover, beans, peas Plants attract bacteria through the release of exudates and enzymes from the roots. Infection and form of root nodules Reduce N2 to ammonia (nitrogen fixation) 15.10 Symbiotic mutualisms are involved in the transfer of nutrients

28. Plant roots and mycorrhizal fungi Fungi assist the plant with the uptake of nutrient from the soil (extended water and nutrients absorption) Plant provides the fungi with carbon, a source of energy. Endomycorrhizae (a) And ectomycorrhizae (b)

29. Example one: Plant and fungi Plant provide food to fungi in the form of photosynthates Fungi defend the host plant against grazing by producing alkaloids compounds in the tissue of host grasses (tastes bitter, toxic). Example two: cleaning mutualism Cleaner-shrimp and cleaner-fish 15.11 Some symbiotic mutualisms are defensive Moray eel Red-billed oxpecker

30. Not necessary to be symbiotic Example: plant-pollinator relationship (insects, birds) Seed dispersal (birds, ants) 15.12 Mutualisms may be nonsymbiotic wasp and orchid bleeding heart and elaiosome cedar waxwing

31. 15.13 Mutualism can influence population dynamics • Symbiotic mutualism: depends on each other remove one, another can’t grow well or die • Nonsymbiotic mutalism • Difficult to study • Example: pollination, could result extinction, but most of cases, subtle effects • Mutualism can involve multiple species and affect the community • Oaks • Truffles • Voles • Pigs (search truffles) • Humans (eat truffles)

32. 15.14 A simple model of mutualistic interactions • Lotka-Voltrra mutualism model species 1 species 2 • Very similar to two species competition model • Alphas are positive interaction coefficients

33. A model of mutualistic interactions • Solve the equation (zero isolines) • dN1/dt=0, N2=(K1-N1)/(a2,1) • dN2/dt=0, N2=(k2+(a2,1)N1) r1=3.22, k1=1000,alpha12=0.5 r2=3.22, k2=100, alpha21=0.6 Stable co-existence With higher K values

34. Population trajectories When projected, it is showed that carrying capacity of each species is increased by the presence of another mutualist.

35. End

36. Mutualisms can be classified ecologically: • Trophic--specialized partnerships for obtaining energy and nutrients • Corals (algae & zoozanthellae) • Nitrogen-fixing bacteria (e.g., rhizobium & plant) • Ectotrophic mycorrhizae & plants • Lichens (fungus & alga) • Defensive--partnerships providing protection against herbivores, predators, or parasites • Cleaner fish • Ant-Acacia (ants protect against herbivores) • Dispersive--partnerships in which animals disperse pollen or seeds of plants, generally for food reward • Flower-pollinator • Fruit-seed disperser