evolutionary rescue - senecio7の日記

Wilson BA, Pennings PS & Petrov DA 2017 Soft selective sweeps in evolutionary rescue. Genetics 205:1573-1586.

(Wilson et al. 2014)
we had assumed that demography was independent of the allelic state at the locus under selection
an assumption that is valid only under models where fitness advantages are relative and density independent
(e.g., the standard Wright–Fisher model with selection or the Moran model)
in this article, we allow adaptation to influence demography
fitness advantages are absolute and density dependent within the context of an evolutionary rescue scenario

when rescue is likely to occur, it is more likely to occur via soft selective sweeps than hard selective sweeps
this result follows intuitively from the observation that the higher the time-averaged input of adaptive mutations, the greater the probability of evolutionary rescue as well as the probability of soft selective sweeps
our results highlight a key correlation between genetic diversity following evolutionary rescue and the likelihood of evolutionary rescue

the wild-type population size can be deterministically approximated by w(t) = w₀exp(−αt)
α = d_w − b_w
Orr and Unckless (2008) found the probability of evolutionary rescue to be approximately twofold higher for wild-type populations that experience logistic population regulation rather than the strictly exponential decline
we will focus strictly on the case of exponential decline for model simplicity

the decline in the wild-type population means that adaptation will eventually be mutation limited in all cases

the hallmark of a soft selective sweep is that multiple lineages are preserved after selection
selection need not remove all genetic diversity in a population following evolutionary rescue, especially when rescue is expected to be common

adaptive mutants are absent at the onset of an environmental shift
they are strongly deleterious in the prior environment, as can be the case in resistance evolution

when rescue is likely, more adaptive mutants are expected to be involved
we expect soft sweeps to be a general feature of evolutionary rescue in situations where it is most likely to occur
in cases where extinction is likely, evolutionary rescue (should it occur) will occur via hard selective sweeps

we have not considered any neutral loci in the genome, whether linked to the selected locus or not
whether a selective sweep in a rescued population can be detected is a question that deserves separate treatment
selective sweeps will be very hard to detect if the population as a whole goes through a severe bottleneck
in rescued populations, hard sweeps may be harder to detect than soft sweeps
hard sweeps tend to occur when the population bottleneck is more severe