Coevolution Flashcards
(24 cards)
What is the fitness of a trait determined by?
Genotype and abiotic environmet
Genotype x environment interaction
What about the biotic environment?
The abiotic environment changes but doesn’t evolve.
Now fitness is determined by:
genotype x genotype x environment
Describe coevolution
evolutionary change in a trait […] in one population in response
to a trait […] of a second population, followed by an evolutionary
response by the second population to the first.
Evolution of the biotic environment
Describe the types of species level coevolution
Mutualism-antagonism
Mutualistic coevolution: adaptation in one species increases
fitness of the other species - mutualistic interactions
Antagonistic coevolution: adaptation in one species reduces
fitness of other species, e.g host and parasites, prey and
predators
e.g. plasmid pQBR103 allows pseudomonas to detoxify mercury. In the absence of mercury, significant cost if carrying the plasmid. Where interactions sit is environment dependent
Plant-pollinator coevolution
Orchid fly and orchid
Proboscis and thorax of the fly and flower corolla depths and widths were measured
Flower corolla tube length remained a significant predicto of fly proboscis length while fly proboscis length significantly predicted flower corolla length
Predator prey
Garter snake and poisoous newt: perpetual battle for higher prey toxicity and better predator resistance
Host parasite system
e.g. rabbits and myxoma: perpetual battle for better host resistance and higher virus virulence
The red queen hypothesis
Originally used to study macroevolution extinction
probabilities
Species must continually evolve adaptations and counter
adaptations in response to evolutionary changes in other
organisms to avoid extinction
van valen
What are the two types of red queen dynamics?
Directional (escalatory): both antagonists are under selection to exceed the trait of the other species. Selective sweeps
Fluctuating: fluctuating selection drives allele frequency oscillations in both parties
Host parasite coevolution
the collection of hosts a parasite can successfully reproduce on
Specialist parasite can only utilize one or a few hosts
Generalist parasites utilize a wide range of hosts
Bacteriophage life cycle
The burst size can range from just a dozan to thousands
Coevolution leading to changes in parasite host ranges
Phage Ox2 uses two different receptors of E.Coli
Shift from protein to carbohydrate. Host range shifts in T4 coliphages. Multivvalent adsorption of phage phi92. Lambda phage evolves to use a new EColi receptor
Host shifts of bacteriphages
Glucose as a carbon source. λ phage attaches to LamB (maltodextrin). LamB repressed. λ phage to OmpF
What are characteristics patterns determined by?
The genetic mechanism of host-parasite interaction.
Interact in lock and key fashion with receptors and tail fibres
Mutations changing the shape of the bacterial receptors confer resistance
Mutations in the phage lead to the phage tail fibre matching new receptor (but not old one!)
One diallelic locus mediating infection and resistance traits
Effect of bacterial alleles
a Receptor shape a, allows attachment of phage tail fibre a, but
not of tail fibre A
A Receptor shape A, allows attachment of phage tail fibre A, but
not of tail fibre a
Effect of phage alleles
a Phage tail fibre a, allows attachment to bacterial receptor a
A Phage tail fibre A, allows attachment to bacterial receptor A
Resulting host ranges = all phages are specialists
Matching alleles mechanism with coevolutionary dynamics
Common host alleles are targeted by phages resulting in
fluctuating selection
Gene for gene mechanism: T3 phage attaches to LPS chains on E.Coli cells
Mutations truncating LPS chains confer resistance
Mutations in T3 allow binding to truncated LPS
Successive LPS truncations and phage tail fibre mutations = more resistant bacteria and more infective phages
Evolved phages become more and more specialist. New phage matches new AND old receptor
One diallelic locus mediating infection and resistance traits in gene for gene
Effect of bacterial alleles
a LPS chain of length 2, allows attachment of long and short
phage tail fibres
A LPS chain of length 1, allows attachment of short phage tail
fibres
Effect of phage alleles
a Long phage tail fibre
A Short phage tail fibre
Result?
Phages can be specialist (long tail) or generalists (short)
There is a cost for carrying the generalist allele
E Coli and Salmonella model system
Two phages: λ (specialist) and X174 (generalist)
E. has the higher growth rate. E coli is the more profitabe host, with greater burst sizes (lower burst size for generalist)
High density and low density environment
Do high or low host densities favour the generalist or specialist?
Optimal foraging theory
Infecting host cell and completeing the life cycle takes time
Infecting different hosts yields different payoffs
Host densities are fixed. No ecological feedback fm phage attack on host population size
If hosts are abundant: avoid wasting time on low quality
If scarce: take every host you can get
Predictions: low productivity environments should favour generalists. Specialists win at high.
Empirical data of optimal foraging theory?
Host densities are naturally at the lower end of the spectrum, yet specalists are prevalent. Mismatch? optimal foraging theory does not include ecological interactions
Predictions of the eco-evo model?
Low productivity environments with few hosts favour
specialist
Generalist win at high host densities
S. typhimurium can only persist in high productivity
environments where its resistance against λ phage
outweighs its lower growth rate
Thus, at low productivity the specialist phage
outcompetes the costly generalist phage genotpye for
the more profitable host E. coli
At high productivity E. coli goes extinct due to the
combined infection pressure by the two phages
Thus, at high productivity only the generalist phage
ΦX174 can persist on its exclusive host S. typhimurium
Conclusions fo eco-evo model?
Opposite of optimal foraging theory predictions
At bacterial densities closer to natural densities
Coexistence of specialists and generalists is possible
