Transcript Summary of fifth lesson - College of Natural Resources, UC Berkeley

Summary of fifth lesson
• Disease as “disease triangle”, effect of humans, disease
as pant-microbe interaction
• Different types of disease of wild plants
• True effect of disease: fertility+mortality+indirect effect
on pollinators+unfair competitive advantage….but what
about the “ carry over effect”
• Density dependance
Disease and competition
• Competition normally is conducive to
increased rates of disease: limited
resources weaken hosts, contagion is
easier
• Pathogens can actually cryptically drive
competition, by disproportionally
affecting one species and favoring
another
Janzen-Connol
• Regeneration near parents more at risk of becoming
infected by disease because of proximity to mother
(Botryosphaeria, Phytophthora spp.). Maintains
spatial heterogeneity in tropical forests
• Effects are difficult to measure if there is little host
diversity, not enough host-specificity on the pathogen
side, and if periodic disturbances play an important
role in the life of the ecosystem
Diseases and succession
• Soil feedbacks; normally it’s negative. Plants
growing in their own soil repeatedly have
higher mortality rate. This is the main reason
for agricultural rotations and in natural
systems ensures a trajectory towards
maintaining diversity
• Phellinus weirii takes out Douglas fir and
hemlock leaving room for alder
The red queen hypothesis
• Coevolutionary arm race
• Dependent on:
– Generation time has a direct effect on rates of evolutionary
change
– Genetic variability available
– Rates of outcrossing (Hardy-weinberg equilibrium)
– Metapopulation structure
Diseases as strong forces in
plant evolution
• Selection pressure
• Co-evolutionary processes
– Conceptual: processes potentially leading
to a balance between different ecosystem
components
– How to measure it: parallel evolution of
host and pathogen
• Rapid generation time of pathogens. Reticulated
evolution very likely. Pathogens will be selected for
INCREASED virulence
• In the short/medium term with long lived trees a
pathogen is likely to increase its virulence
• In long term, selection pressure should result in
widespread resistance among the host
More details on:
• How to differentiate linear from
reticulate evolution: comparative studies
on topology of phylogenetic trees will
show potential for horizontal transfers.
Phylogenetic analysis neeeded to
confirm horizontal transmission
Phylogenetic
relationships
within the
Heterobasidion
complex
NJ
Het INSULARE
Fir-Spruce
True Fir EUROPE
Spruce EUROPE
True Fir NAMERICA
Pine Europe
Pine EUROPE
Pine N.Am.
Pine NAMERICA
0.05 substitutions/site
NJ
11.10 SISG CA
Geneaology of “S” DNA insertion into
P ISG confirms horizontal transfer.
2.42 SISG CA
BBd SISG WA
F2 SISG MEX
Time of “cross-over” uncertain
NA S
BBg SISG WA
14a2y SISG CA
15a5y M6 SISG CA
6.11 SISG CA
9.4 SISG CA
AWR400 SPISG CA
9b4y SISG CA
15a1x M6 PISG CA
1M PISG MEX
9b2x PISG CA
A152R FISG EU
A62R SISG EU
890 bp
CI>0.9
A90R SISG EU
EU S
A93R SISG EU
J113 FISG EU
J14 SISG EU
J27 SISG EU
J29 SISG EU
0.0005 substitutions/site
EU F
NA P
Complexity of forest diseases
• At the individual tree level: 3
dimensional
• At the landscape level” host diversity,
microclimates, etc.
• At the temporal level
Complexity of forest diseases
• Primary vs. secondary
• Introduced vs. native
• Air-dispersed vs. splash-dispersed, vs.
animal vectored
• Root disease vs. stem. vs. wilt, foliar
• Systemic or localized
Stem canker
on coast live oak
Progression of cankers
Older canker with dry seep
Hypoxylon, a secondary
sapwood decayer will appear
Root disease center in true fir caused by H. annosum
HOST-SPECIFICITY
•
•
•
•
•
Biological species
Reproductively isolated
Measurable differential: size of structures
Gene-for-gene defense model
Sympatric speciation: Heterobasidion,
Armillaria, Sphaeropsis, Phellinus, Fusarium
forma speciales
Phylogenetic
relationships
within the
Heterobasidion
complex
NJ
Het INSULARE
Fir-Spruce
True Fir EUROPE
Spruce EUROPE
True Fir NAMERICA
Pine Europe
Pine EUROPE
Pine N.Am.
Pine NAMERICA
0.05 substitutions/site
Recognition of self vs. non self
• Intersterility genes: maintain species
gene pool. Homogenic system
• Mating genes: recognition of “other” to
allow for recombination. Heterogenic
system
• Somatic compatibility: protection of the
individual.
INTERSTERILITY
• If a species has arisen, it must have some
adaptive advantages that should not be
watered down by mixing with other species
• Will allow mating to happen only if individuals
recognized as belonging to the same species
• Plus alleles at one of 5 loci (S P V1 V2 V3)
MATING
• Two haploids need to fuse to form n+n
• Sex needs to increase diversity: need
different alleles for mating to occur
• Selection for equal representation of
many different mating alleles
SEX
• Ability to recombine and adapt
• Definition of population and
metapopulation
• Different evolutionary model
• Why sex? Clonal reproductive approach
can be very effective among pathogens
Long branches in
between groups
suggests no sex is
occurring in between
groups
NJ
Het INSULARE
Fir-Spruce
True Fir EUROPE
Spruce EUROPE
True Fir NAMERICA
Pine Europe
Pine EUROPE
Pine N.Am.
Pine NAMERICA
0.05 substitutions/site
NJ
11.10 SISG CA
Small branches within a clade
indicate sexual reproduction is
ongoing within that group of
individuals
2.42 SISG CA
BBd SISG WA
F2 SISG MEX
NA S
BBg SISG WA
14a2y SISG CA
15a5y M6 SISG CA
6.11 SISG CA
9.4 SISG CA
AWR400 SPISG CA
9b4y SISG CA
15a1x M6 PISG CA
1M PISG MEX
9b2x PISG CA
A152R FISG EU
A62R SISG EU
A90R SISG EU
890 bp
CI>0.9
EU S
A93R SISG EU
J113 FISG EU
J14 SISG EU
J27 SISG EU
J29 SISG EU
0.0005 substitutions/site
EU F
NA P