Transcript DISEASES AND TREES - UC Berkeley College of Natural Resources

Summary of previous lesson
• Janzen-Connol hypothesis; explanation of why diseases lead
to spatial heterogeneity
• Diseases also lead to heterogeneity or changes through time
– Driving succession
– The Red Queen Hypothesis: selection pressure will increase number of
resistant plant genotypes
• Co-evolution: pathogen increase virulence in short term, but
in long term balance between host and pathogen
• 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
NJ
Phylogenetic relationships
within the Heterobasidion
complex
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
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Biological species
Reproductively isolated
Measurable differential: size of structures
Gene-for-gene defense model
Sympatric speciation: Heterobasidion,
Armillaria, Sphaeropsis, Phellinus,
Fusarium forma speciales
NJ
Phylogenetic relationships
within the Heterobasidion
complex
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.
Recognition of self vs. non self
• What are the chances two different
individuals will have the same set of VC
alleles?
• Probability calculation (multiply frequency
of each allele)
• More powerful the larger the number of loci
• …and the larger the number of alleles per
locus
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