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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 Phylogenetic relationships relationships within the within the HeterobasidionHeterobasidion complexcomplex
Het INSULARE
True Fir EUROPE
Spruce EUROPE
True Fir NAMERICA
Pine EUROPE
Pine NAMERICA
0.05 substitutions/site
NJ
Fir-SpruceFir-Spruce
Pine EuropePine Europe
Pine N.Am.Pine N.Am.
Geneaology of “S” DNA insertion into Geneaology of “S” DNA insertion into P ISG confirms horizontal transfer.P ISG confirms horizontal transfer.
Time of “cross-over” uncertainTime of “cross-over” uncertain
11.10 SISG CA
2.42 SISG CA
BBd SISG WA
F2 SISG MEX
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
A93R SISG EU
J113 FISG EU
J14 SISG EU
J27 SISG EU
J29 SISG EU
0.0005 substitutions/site
NJ
890 bpCI>0.9
NA S
NA P
EU S
EU F
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 cankerStem cankeron coast live oakon coast live oak
Progression of cankersProgression of cankers
Older canker with dry seepOlder canker with dry seep
HypoxylonHypoxylon, a secondary , a secondary sapwood decayer will appearsapwood decayer will appear
Root disease center in true fir caused by Root disease center in true fir caused by H. annosumH. 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 Phylogenetic relationships relationships within the within the HeterobasidionHeterobasidion complexcomplex
Het INSULARE
True Fir EUROPE
Spruce EUROPE
True Fir NAMERICA
Pine EUROPE
Pine NAMERICA
0.05 substitutions/site
NJ
Fir-SpruceFir-Spruce
Pine EuropePine Europe
Pine N.Am.Pine N.Am.
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 Long branches in between groups between groups suggests no sex is suggests no sex is occurring in between occurring in between groupsgroups
Het INSULARE
True Fir EUROPE
Spruce EUROPE
True Fir NAMERICA
Pine EUROPE
Pine NAMERICA
0.05 substitutions/site
NJ
Fir-SpruceFir-Spruce
Pine EuropePine Europe
Pine N.Am.Pine N.Am.
Small branches within a clade Small branches within a clade indicate sexual reproduction is indicate sexual reproduction is
ongoing within that group of ongoing within that group of individualsindividuals
11.10 SISG CA
2.42 SISG CA
BBd SISG WA
F2 SISG MEX
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
A93R SISG EU
J113 FISG EU
J14 SISG EU
J27 SISG EU
J29 SISG EU
0.0005 substitutions/site
NJ
890 bpCI>0.9
NA S
NA P
EU S
EU F
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