Transcript Lecture 14

BIOL 4120: Principles of Ecology
Lecture 14: Parasitism and
Mutualism
Dafeng Hui
Room: Harned Hall 320
Phone: 963-5777
Email: [email protected]
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
15.1 Parasites draw resources from host
organisms
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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)
Parasites draw resources from host
organisms
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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
15.2 Hosts provide diverse habitats for
parasites
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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
Hosts provide diverse habitats for
parasites
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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.
15.3 Direct transmission can occur
between host organisms
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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)
Direct transmission can occur between
host organisms
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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)
15.4 Indirect transmission involves an
intermediate vector
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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.
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Mosquito
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•
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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
Indirect transmission involves an
intermediate vector
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Plant
Elm bark beetles
• Fungi
• Cause devastating Dutch elm disease from tree to tree
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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.
Birds and mistletoe
15.5 Transmission can involve multiple
hosts and stages
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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
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.
15.6 Host respond to parasitic invasions
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Adaptations of host species to minimize the impact
of parasite
• Reduce parasitic invasion
• Combat parasitic infection once it has occurred
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Host response to parasite
• Avoidance
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Birds and mammals, grooming
Birds, preening
Deer seek dense and shaded places to avoid deerflies
• Inflammatory response in animals
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Stimulate secretion of histamines (chemical alarm
signals), induce increased blood flow to site, resulting
inflammatory
• Gall formation in plants
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Abnormal growth structure
Cut off contact of fungus with health tissue
Host respond to parasitic invasions
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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
• Immune response in animals
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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.
15.7 Parasites affect host survival and
reproduction
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Parasites affect host survival and reproduction
• Malaria in humans
• Malaria on western fence lizard
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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
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Parasites can increase mortality that can result
from indirect consequences of infection
Infection of the California killfish
15.7 Parasites may regulate host
populations
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Parasites can be major
regulators of population
• Plants
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Chestnut blight, nearly
exterminated the American
chestnut
Dutch elm disease, nearly
removed American elm from
North America
• Humans
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Black Death in14th century
Smallpox in 18th century
Cholera in 19th century
Parasites may act as a selective agent of
mortality, infecting only a subset of the
population.
Parasites may regulate host populations
• Black Death in14th century
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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
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Needs even high human population due to direct transmission
Halted by human evolution
• Vaccination
• Cholera in 19th century
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Needs even higher density and water/food transmitted
Halted by human evolution
• Clean water supply and bacteriology
• AIDS in 21st century
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Needs even higher population density
• Never a problem in low density central African origin except to some
villages
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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
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Halted by
• Change in human behavior?
• Science?
15.9 Parasitism can evolve into a positive
relationship
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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
Commensalism
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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
Commensalism between cattle (as food
beaters) and cattle egrets (three white
birds, one sitting on cow) in Jamaica
Mutualism
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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.
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Lichens: symbiotic association
A fungus and an alga combined to form a
spongy body (thallus).
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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
Mutualism – more examples
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Plants and
pollinators
Plant and
mycorrhizal fungi
• Ash tree and
mycorrhizal fungi
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Corals and
zooxanthellae
Phainopepla and
mistletoe
15.10 Symbiotic mutualisms are involved
in the transfer of nutrients
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)
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)
15.11 Some symbiotic mutualisms are
defensive
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
Moray eel
Red-billed
oxpecker
15.12 Mutualisms may be nonsymbiotic
Not necessary to be symbiotic
Example:
plant-pollinator relationship (insects, birds)
Seed dispersal (birds, ants)
wasp and orchid
bleeding heart and elaiosome
cedar waxwing
15.13 Mutualism can influence population
dynamics
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Symbiotic mutualism: depends on each other
remove one, another can’t grow well or die
Nonsymbiotic mutalism
• Difficult to study
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Example: pollination, could result extinction, but most of cases,
subtle effects
Mutualism can involve multiple species and affect the
community
• Oaks
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Truffles
Voles
Pigs (search truffles)
Humans (eat truffles)
15.14 A simple model of mutualistic
interactions
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Lotka-Voltrra mutualism model
species 1
species 2
dN1
K1  N1   21 N 2
 r1 N1 (
)
dt
K1
dN 2
K 2  N 2  12 N1
 r2 N 2 (
)
dt
K2
• Very similar to two species competition model
• Alphas are positive interaction coefficients
A model of mutualistic interactions
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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
Population trajectories
When projected, it is
showed that carrying
capacity of each
species is increased by
the presence of another
mutualist.
End
Mutualisms can be classified ecologically:
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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