Summary of fifth lesson Disease as disease triangle

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 Fir-Spruce Pine Europe Pine N. Am.

Geneaology of “S” DNA insertion into P ISG confirms horizontal transfer. NA S Time of “cross-over” uncertain NA P 890 bp CI>0. 9 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 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 Fir-Spruce Pine Europe 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 V 1 V 2 V 3)

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 Fir-Spruce Pine Europe Pine N. Am.

Small branches within a clade indicate sexual reproduction is ongoing within that group of individuals NA S NA P 890 bp CI>0. 9 EU S EU F