absolute fitness - senecio7の日記

Anciaux Y, Chevin L-M, Ronce O & Martin G 2018 Evolutionary rescue over a fitness landscape. Genetics 209:265-279.

we will focus on the case where environmental stress causes a reduction of population mean fitness that is harsh enough to trigger a decline in abundance

discrete genetic models, and quantitative genetic models
discrete genetic models assume a narrow genetic basis for adaptation (and ER)
a single beneficial mutation can rescue an otherwise monomorphic population
quantitative genetics models of ER inherently address the influence of stress on the rate of adaptation by assuming that adaptation (and ER) is caused by evolution of a quantitative trait whose optimum changes with the environment
both the rate of population decline and the rate of adaptation under stress depend on the distance between the phenotypic optima in the past and present environments

we combine this FGM with population dynamic approaches that account for demographic and evolutionary stochasticity

our simulations below are performed for discrete generations with Poisson offspring distributions

in the SSWM regime at mutation-selection balance, most segregating phenotypes remain within a narrow neighborhood of the optimum
so the mutation-selection balance is well-approximated by assuming that all mutations originate from the optimum phenotype
this is essentially the House-of-Cards approximation (Turelli 1984) extended to the FGM of arbitrary dimensionality

we tracked the population size and genetic composition of a population across discrete, nonoverlapping generations
the size N_{t + 1} of population at generation t + 1 was drawn as a Poisson number N_{t + 1} ~ Poisson(N_t W), with W = e^r the mean multiplicative fitness (W = e^r) and N_t the population size, in the previous generation
the genotypes forming this new generation were then sampled with replacement from the previous one with weight W_i = e^r_i
this is faster and exactly equivalent to drawing independent Poisson reproductive outputs for each individual, or genotype

a population was considered rescued when it reached a population size N_t and mean growth rate r_t such that its ultimate extinction probability, if it were monomorphic, would lie below 10⁻¹²
exp(−2 N_t r_t) < 10⁻¹²