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