Adaptive dynamics theory Flashcards
(19 cards)
What are the limitations of R0 maximisation?
R0 is not necessarily always maximised by evolution
If N1 has spread and substantial parts of the population have become infected the success of a new strain is no longer determined by its performance in the initial environment
In the case of pathogen evolution, what if the host also evolves?
No general optimisation principle can predict adequately the evolutionary outcome of all possible arms races.
We need to consider the potential for the invasion of a variant pathogen or host type into the environment jointly created by the current prevalent pathogen and host types.
Describe environmental feedback in evolution
Whenever an ecological system adapts, its affects its environment
Adaptive change depends on the environmental conditions which in turn are altered by adaptive change.
Describe environmental feedback in evolution using Rabbits and myxoma
Once the virus had evolved a lower virulence, the density of rabbits increased.
This change in the virus’s environment in turn affected the way the virus spread.
By the time rabbits had evolved higher resistance, the proportion of rabbits carrying the virus had changed.
This change influenced the likelihood that a rabbit would become infected, and thus the demography of the rabbit population.
Describe the theory of adaptive dynamics
Closes the environmental feedback loop
Studies the dynamics of longterm phenotypic evolution. The fitness of organisms can only be evaluated relative to the environment in which they live.
What are the assumptions of the adaptive dynamics theory?
Individuals reproduce asexually and the offspring is phenotypically identical to the parent.
Phenotype under consideration can vary continuously (one dimensional trait space).
Mutations are random but have small phenotypic effect.
Mutations occur sufficiently infrequently so that the population has reached its ecological steady state before a new mutant comes along.
Describe pairwise invasibility plot
A graphic way of determining which mutant can invade which resident populations
mutant’s trait > resident’s trait
mutant’s fitness < 0
mutant becomes extinct
Describe PIP identification and evolutionary outcomes
Evolutionary stability
Convergence stability
Invasion potential
Mutual invasibility
PIP clearly idenfity potential evolutionary endpoints at which selection pressures vanish. These potential endpoints are called evolutionary singular strategies and are characterised by the properties above
Evolutionary stability
Is an evolutionary singular strategy immune to invasion by neighbouring phenotypes?
Yes = ESS
The vertical line lies completely where mutants fitness < 0
Convergence stability
When starting from neighbouring phenotypes, do successful invaders lie closer to the evolutionary single strategy?
Yes = convergence
Mutant fitness > 0 above the diagonal on the left of the singularity and below on the diagonal on the right
Invasion potential
Is the evolutionary singular strategy able to invade populations of neighbouring phenotypes?
Horizontal line through the singularity lies completely in the region where mutants fitness > 0
Mutual invasibility
If a pair of neighbouring phenotypes lie on either side of the evolutionary singular strategy, can they invade each other?
Secondary diagonal lies in teh region where mutants fitness > 0
Evolutionary stability and convergence stability
Continuously stable strategy
Evolutionary stability without convergence stability
Although the evolutionary singular strategy is resistant against invasions from all nearby phenotypes, it cannot be reached by small mutational steps - Garden of Eden
Convergence stability without evolutionary stability
In the absence of evolutionary stability, selection becomes disruptive near a convergence-stable singularity. Two phenotypically distinct subpopulations can then diverge from around the singularity in a process called evolutionary branching
Describe evolutionary branching
According to the adaptive dynamicists, studies of evolutionary branching have opened up new avenues for understanding the origin of new species, the composition of ecological communities, and the formation of biodiversity.
Testing the adaptive dynamics theory
E.Coli is grown into an environment containing two resources: glucose and acetate
Converge, then diversify into two specialists
Describe the “war”
Population genetics does not mention adaptive dynamics theory
Population genetics vs adaptive dynamics
Population genetics:
does not take ecology and environment into consideration
genotypes have fixed fitnesses
Adaptive dynamics:
does not take into account genetic detail
fitness is not fixed but depends on the environment
