Download C. Predation, Herbivory, and Parasitism

Coevolution
Coevolution
I.
Types of Interactions
A. Overview:
Effect on Species 2
Positive
Effect on species 1
Positive
Neutral
Negative
Neutral
Negative
Coevolution
I.
Types of Interactions
A. Overview:
Effect on Species 2
Positive
Neutral
Negative
Positive
mutualism
commensal
consumer
Neutral
commensal
-
amensal
Negative
consumer
amensal
competition
Effect on species 1
Co-evolution requires reciprocal evolutionary feedbacks… such that response by one species affects
the selective pressures on another that encourage further responses.
Coevolution
I.
Types of Interactions
A. Overview:
B. Competition:
- the nature of the interaction: scramble (for resource) or contest (access)
Coevolution
I.
Types of Interactions
A. Overview:
B. Competition:
- intraspecific competition:
- for food, mates, territories
Coevolution
I.
Types of Interactions
A. Overview:
B. Competition:
- interspecific competition:
- for food (nutrients), territories
Coevolution
I.
Types of Interactions
A. Overview:
B. Competition:
- outcomes:
1. reduction in growth, reproduction of
individuals or populations.
2. local extinction (competitive exclusion)
3. Resource Partitioning and Character Displacement
Coevolution
I.
Types of Interactions
A. Overview:
B. Competition:
- outcomes:
- not coevolution.
Once one species reduces the intensity of the interaction, selection
pressures on the second species are RELAXED, stimulating no further
change.
Competition
Coevolution
I.
Types of Interactions
A. Overview:
B. Competition:
C. Predation, Herbivory, and Parasitism:
Toxicity
Coevolution
I.
Mimicry
Types of Interactions
A. Overview:
B. Competition:
C. Predation, Herbivory, and Parasitism:
- selects for defense in prey
Resistance (encapsulate wasp egg)
Avoidance
crypsis
Coevolution
I.
Types of Interactions
A. Overview:
B. Competition:
C. Predation, Herbivory, and Parasitism:
- selects for defense in prey
- Response exerts a pressure on predator:
‘coevolution’ (arms race)
“you must keep running to stay in the same place”
The ‘Red Queen Hypothesis’
Predation
Coevolution
I.
Detection, and
capture
Types of Interactions
A. Overview:
B. Competition:
C. Predation, Herbivory, and Parasitism:
- selects for defense in prey
- Response exerts a pressure on predator:
‘coevolution’ (arms race)
- selects for:
‘resistance to ‘resistance’
Detoxification
C. Predation, Herbivory, and Parasitism:
- Results: Geographic variation in Relationships
‘Mosaic theory of coevolution'
Coevolution
I.
Types of Interactions
A. Overview:
B. Competition:
C. Predation, Herbivory, and Parasitism
Batesian Mimicry is an ‘arms race’
Toxic species gains protection from predators
‘aposematic coloration’
Selection favors harmless mimics that look like
toxic species.
This weakens the correlation between toxicity
and coloration, selecting for changes in toxic
species so it can be recognized as toxic.
Three toxic species
Papilio dardanus
C. Predation, Herbivory, and Parasitism:
- Results: Geographic variation in Relationships
C. Predation, Herbivory, and Parasitism:
- Results: Geographic variation in Relationships
C. Predation, Herbivory, and Parasitism:
- Results: Coevolutionary alternation
Cuckoo – parasitizes 4 bird
species in England. Lays eggs in
their nests.
Reed Warbler
Cuckoo chick
pushes other
eggs and
nestlings out
of the nest
Hard work
feedin the
cuckoo chick…
C. Predation, Herbivory, and Parasitism:
- Results: Coevolutionary alternation
Reed Warbler
(discriminates)
Pied Wagtail
(discriminates)
Cuckoo – parasitizes 4 bird
species in England. Lays eggs in
their nests.
Dunnock – no discrimination
C. Predation, Herbivory, and Parasitism:
- Results: Coevolutionary alternation
Reed Warbler
(discriminates)
Pied Wagtail
(discriminates)
Sp. 1
responds
Cuckoo – parasitizes 4 bird
species in England. Lays eggs in
their nests.
Dunnock – no discrimination
C. Predation, Herbivory, and Parasitism:
- Results: Coevolutionary alternation
Reed Warbler
(discriminates)
Pied Wagtail
(discriminates)
Sp. 1
responds
Cuckoo – parasitizes 4 bird
species in England. Lays eggs in
their nests.
Sp. 1
responds
Dunnock – no discrimination
C. Predation, Herbivory, and Parasitism:
- Costs: Defenses are expensive
Selected lines exposed to parasites encapsulate eggs
at a greater rate than naïve flies
When placed in competition with populations
unexposed to wasps, they lose when resources
become limiting (competition intense).
C. Predation, Herbivory, and Parasitism:
- Costs: Defenses are expensive
Relaxation of selection causes
reversion to asexual reproduction.
Wildtype outcrossing rates over time. Outcrossing rates in
wildtype populations were not manipulated and free to
evolve during the experiment. The wildtype populations
were exposed to three different treatments: control (no S.
marcescens; dotted line), evolution (fixed strain of S.
marcescens; dashed line), and coevolution (coevolving S.
marcescens; solid line) for thirty generations. Error bars
represent two standard errors of the mean (SE).
C. Predation, Herbivory, and Parasitism:
- Parasitism is a bit different
Predators want to kill prey ASAP – to reduce period of interaction
Parasites that kill their host before dispersal are selected against.
Why are pathogens virulent?
C. Predation, Herbivory, and Parasitism:
- Parasitism is a bit different
Why are pathogens virulent?
- coincidental evolution hypothesis: Some are deadly
by chance. They don't mean to kill you, it just
happens. The soil bacterium Clostridium tetani
produce a potent neurontoxin as a secondary
metabolite (just as a consequence of their
metabolism). This metabolite is a strong neurotoxin
that kills human hosts. But, C. tetani does not
normally live in humans. The evolution of this toxin
was probably NOT a response to the dynamic
relationship between humans and the bacterium.
Perhaps it is to kill soil nematodes - a major
competitor in the soil microfauna.
C. Predation, Herbivory, and Parasitism:
- Parasitism is a bit different
Why are pathogens virulent?
- short-sighted evolution hypothesis: the
pathogen may go through several generations inside
the host, and selection will favor within-host fitness
over traits which might increase the probability of
host survival. So, a strain might cripple it's host as it is
selected for within that host (over other strains that
are nor as damaging).
Organismal Selection overriding Group Selection.
C. Predation, Herbivory, and Parasitism:
- Parasitism is a bit different
Why are pathogens virulent?
- trade-off hypothesis: virulence and
transmission are intimately related. Virulence can
increase if transmission increases or stays high. But,
if population density of hosts decline, then
transmission will probably decline and natural
selection will favor strains that do not kill their host.
Living hosts are more likely to encounter new hosts
and transmit the pathogen than dead hosts...
(except that cultural practices become important....
handling and burying the dead, or eating tissue from
dead bodies, can increase transmission regardless of
density and maintain virulence, as well.)
Deadly pathogens (Ebola) have to be highly
contagious to survive.
Myxoma and rabbits in Australia
C. Predation, Herbivory, and Parasitism:
- Parasitism is a bit different
Why are pathogens virulent?
How do they overwhelm host immunity? – MUTATION RATE
- HIV - The reverse transcriptases that make the DNA from RNA are error-prone HIV has the highest mutation rate of any virus or organism measured - over 1/2 of
the reverse transcriptases made have a new mutation.
- AZT - reverse transcription inhibitor - it is a base analog that, when incorporated,
stops transcription because it has a N-group instead of a 3' OH group. Other reverse
transcriptase inhibitors lock up the active site.
Thus, there is rapid selection for rt'ases that fail to bind AZT - rendering this
treatment ineffective in 6 months. But, these new variants do not replicate as
quickly; so when AZT treatment is stopped, there is reverse selection for original
variant that reproduces more rapidly, and AZT is again effective.
Trade-offs
C. Predation, Herbivory, and Parasitism:
- Parasitism is a bit different
Why are pathogens virulent?
How do they overwhelm host immunity? – MUTATION RATE
- HIV - The reverse transcriptases that make the DNA from RNA are errorprone - HIV has the highest mutation rate of any virus or organism measured over 1/2 of the reverse transcriptases made have a new mutation. Thus, there
is rapid selection for rt'ases that fail to bind AZT - rendering this treatment
ineffective in 6 months. But, these new variants do not replicate as quickly; so
when AZT treatment is stopped, there is reverse selection for original variant
that reproduces more rapidly, and AZT is again effective.
• HIV variants exist that are not as virulent. However, neither are they as
transmissible. So, they are rare in the population.
Trade-offs
C. Predation, Herbivory, and Parasitism:
- Parasitism is a bit different
Why are pathogens virulent?
How do they overwhelm host immunity? – MUTATION RATE
- HIV - There are also resistant people, who have a mutant
coreceptor protein with a 32 base deletion. THis is called 'delta-32".
Viruses attacking these people can't bind the coreceptor, and thus
can't infect the cells. The frequency of this variant varies across
human populations, up to 9% in some northern European countries.
(Non-existent in Africa or Asia). It may be high because it conferred
advantages to previous plagues like smallpox or even bubonic
plague (bacterial).
C. Predation, Herbivory, and Parasitism:
- Parasitism is a bit different
Why are pathogens virulent?
How do they overwhelm host immunity? – VIRAL TRANSDUCTION INCREASING VARIANCE
FLU
•Hemagluttinin is a surface protein. New viral strains evolve that have new AA sequences
in these surface proteins that are not bound by existing antibodies; requiring a novel
immune response.
• Some sites are antigenic sites that the antibodies respond to.
• Over 20 years, the flu has evolved and the surviving strain is the one with the greatest
frequency of mutations in the antigenic sites. Selection by the human immune system
has favored amino acid changes in the antigenic sites.
• Over the last eleven outbreaks, nine occurred with the strain from the previous year
that had the greatest number of changes in the 18 codons of the antigenic sites.... gives
some predictive ability
• If a radical new sequence evolved, it could crate a pandemic. This is possible, because
infection with multiple virions allow for recombination of the eight chromosomes in the
new viruses. Sometimes, cross infection of non humans by human influenza and pig or
avian flu creates new genetic combinations that can reinfect humans and have entirely
different antigenic sites. (Bird flu, swine flu, etc...)