New Host – parasite coevolutiongow/biol418/pdf/8a_Host... · 2008. 3. 18. · Optimal virulence:...
Transcript of New Host – parasite coevolutiongow/biol418/pdf/8a_Host... · 2008. 3. 18. · Optimal virulence:...
Host –
parasite coevolution
Host-parasite relationship:
Host-parasite coevolutionBiol 418: Evolutionary EcologyHost-parasite coevolution
Jennifer Gow
Examples: a broad church
Diverse interactions and consequences between species:
Host-parasite coevolutionBiol 418: Evolutionary EcologyHost-parasite coevolution
Jennifer Gow
Biol 418: Evolutionary EcologyHost-parasite coevolution
Jennifer Gow
Host: Wood louse, Armadillidium vulgare
Parasite:Wolbachia bacterium
Examples: a broad churchIntracellular symbionts
Host-parasite coevolution
Host: Hypolimnas bolina
Overview
Parasite’s perspective: Optimal virulence
Host’s perspective: Trade-offs in resistance/defence
The host-parasite interaction: Arms races
Host-parasite coevolutionBiol 418: Evolutionary EcologyHost-parasite coevolution
Jennifer Gow
Overview
Parasite’s perspective: Optimal virulence•Myxoma virus
•Transmission mode
•Direct versus vector borne
•Water borne
•Horizontal versus vertical
Host-parasite coevolutionBiol 418: Evolutionary EcologyHost-parasite coevolution
Jennifer Gow
Optimal virulence
Virulence = the damage that a parasite does to its host
Many commensalisms and mutualisms began as host-parasite interactions
Disease outbreaks where virulence reduced
=> host-parasite interactions become commensal or mutualistic?
Biol 418: Evolutionary EcologyHost-parasite coevolution
Jennifer Gow
Host-parasite coevolution
Optimal virulence:Myxoma virus
Transmission mode
Direct versus vector borne
Water borne
Horizontal versus vertical
Rabbit Oryctolagus cuniculus
Optimal virulence:Myxoma virus
Biol 418: Evolutionary EcologyHost-parasite coevolution
Jennifer Gow
Host-parasite coevolution
Optimal virulence:Myxoma virus
Transmission mode
Direct versus vector borne
Water borne
Horizontal versus vertical
Optimal virulence: myxoma virus
Biol 418: Evolutionary EcologyHost-parasite coevolution
Jennifer Gow
Host-parasite coevolution
Fenner (1983) Proc. Roy. Soc. B 218: 259-285.
Virulence class (fatality rate)I II III IV V
(>99% <50%)
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1953
1950
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1961
1965
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Relat
ive fr
eque
ncy
Australia
Optimal virulence:Myxoma virus
Transmission mode
Direct versus vector borne
Water borne
Horizontal versus vertical
Optimal virulence: myxoma virus
Biol 418: Evolutionary EcologyHost-parasite coevolution
Jennifer Gow
Host-parasite coevolution
Fenner (1983) Proc. Roy. Soc. B 218: 259-285.
Skin titre of virus increases with virulence class
I II III IV V0Mo
squit
o tra
nsmi
ssion
eff
icien
cy
Optimal virulence:Myxoma virus
Transmission mode
Direct versus vector borne
Water borne
Horizontal versus vertical
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100
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100
France1953
1962
1968
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Britain1953
1962
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Optimal virulence: myxoma virus
Biol 418: Evolutionary EcologyHost-parasite coevolution
Jennifer Gow
Host-parasite coevolution
Fenner (1983) Proc. Roy. Soc. B 218: 259-285.
Virulence classI II III IV V(>99% <50%) Virulence class
I II III IV V(>99% <50%)
Optimal virulence:Myxoma virus
Transmission mode
Direct versus vector borne
Water borne
Horizontal versus vertical
Optimal virulence: transmission mode
Biol 418: Evolutionary EcologyHost-parasite coevolution
Jennifer Gow
Host-parasite coevolution
Hypothesis: for internal parasites, probability of transmission to new hosts may be increased if pathogen multiplies rapidly within an infected host even while it causes the host to become very ill.
Therefore, virulence should evolve according to mode and probability of transmission.
Optimal virulence:Myxoma virus
Transmission mode
Direct versus vector borne
Water borne
Horizontal versus vertical
Optimal virulence: transmission mode
Biol 418: Evolutionary EcologyHost-parasite coevolution
Jennifer Gow
Host-parasite coevolution
Optimal virulence:Myxoma virus
Transmission mode
Direct versus vector borne
Water borne
Horizontal versus vertical
Ewald (1993) Sci. Am. 268 (April): 86-93.
Optimal virulence: transmission mode
Biol 418: Evolutionary EcologyHost-parasite coevolution
Jennifer Gow
Host-parasite coevolution
Ewald (1993) Sci. Am. 268 (April): 86-93.
Optimal virulence:Myxoma virus
Transmission mode
Direct versus vector borne
Water borne
Horizontal versus vertical
Optimal virulence: transmission mode
Biol 418: Evolutionary EcologyHost-parasite coevolution
Jennifer Gow
Host-parasite coevolution
Virulence should evolve according to mode and probability of transmission:
Increased opportunities for parasite transmission will permit the evolution of increased virulence.
Restricted opportunities for transmission promote less virulent parasite interactions.Optimal virulence:
Myxoma virus
Transmission mode
Direct versus vector borne
Water borne
Horizontal versus vertical
Optimal virulence: transmission mode
Biol 418: Evolutionary EcologyHost-parasite coevolution
Jennifer Gow
Host-parasite coevolution
Vertical transmission:
Horizontal transmission: Optimal virulence:
Myxoma virus
Transmission mode
Direct versus vector borne
Water borne
Horizontal versus vertical
Optimal virulence: transmission mode
Biol 418: Evolutionary EcologyHost-parasite coevolution
Jennifer Gow
Host-parasite coevolution
Virulence should evolve according to mode and probability of transmission:
Increased opportunities for parasite transmission will permit the evolution of increased virulence.
Restricted opportunities for transmission promote less virulent parasite interactions.
Optimal virulence:Myxoma virus
Transmission mode
Direct versus vector borne
Water borne
Horizontal versus vertical
Optimal virulence: transmission mode
Biol 418: Evolutionary EcologyHost-parasite coevolution
Jennifer Gow
Host-parasite coevolution
Species-specific nematodes parasitizing fig-pollinating wasps
Species specific relationships:• Wasps enter fig, lay eggs which grow and mate before dispersal.
• Nematode attach to young wasp which they parasitize before emerging in new fig to mate. Eggs hatch synchronously with wasp eggs.
Opportunities for transmission depend on how many foundresses per fig:
In some species, wasp broods tend to be from single foundresses
…in others, from multiple foundresses
Herre (1993) Science 259: 1442-5.
Optimal virulence:Myxoma virus
Transmission mode
Direct versus vector borne
Water borne
Horizontal versus vertical
Optimal virulence: transmission mode
Biol 418: Evolutionary EcologyHost-parasite coevolution
Jennifer Gow
Host-parasite coevolution
Herre (1993) Science 259: 1442-5.
Species-specific nematodes parasitizing fig-pollinating wasps
Dec
reas
ing
viru
lenc
e
Opportunity for (horizontal) transmission
Optimal virulence:Myxoma virus
Transmission mode
Direct versus vector borne
Water borne
Horizontal versus vertical
Optimal virulence: transmission mode
Biol 418: Evolutionary EcologyHost-parasite coevolution
Jennifer Gow
Host-parasite coevolution
Barley and barley stripe mosaic virus
Stewart et al. (2005) Evolution 59: 730-739.
Optimal virulence:Myxoma virus
Transmission mode
Direct versus vector borne
Water borne
Horizontal versus vertical
Virulence = % unviable seeds
Optimal virulence: transmission mode
Biol 418: Evolutionary EcologyHost-parasite coevolution
Jennifer Gow
Host-parasite coevolution
Stewart et al. (2005) Evolution 59: 730-739.
Barley and barley stripe mosaic virus
Optimal virulence:Myxoma virus
Transmission mode
Direct versus vector borne
Water borne
Horizontal versus vertical
Optimal virulence: transmission mode
Biol 418: Evolutionary EcologyHost-parasite coevolution
Jennifer Gow
Host-parasite coevolution
Stewart et al. (2005) Evolution 59: 730-739.
Barley and barley stripe mosaic virus
Optimal virulence:Myxoma virus
Transmission mode
Direct versus vector borne
Water borne
Horizontal versus vertical
Overview
Parasite’s perspective: Optimal virulence
Myxoma virus
Transmission mode
Direct versus vector borne
Water borne
Horizontal versus vertical
Host-parasite coevolutionBiol 418: Evolutionary EcologyHost-parasite coevolution
Jennifer Gow