Some consequences of demographic stochasticity in population genetics.
Much of population genetics is based on the diffusion limit of the Wright-Fisher model, which assumes a fixed population size. This assumption is violated in most natural populations, particularly for microbes. Here we study a more realistic model that decouples birth and death events and allows for a stochastically varying population size. Under this model, classical quantities such as the probability of and time before fixation of a mutant allele can differ dramatically from their Wright-Fisher expectations. Moreover, inferences about natural selection based on Wright-Fisher assumptions can yield erroneous and even contradictory conclusions: at small population densities one allele will appear superior, whereas at large densities the other allele will dominate. Consequently, competition assays in laboratory conditions may not reflect the outcome of long-term evolution in the field. These results highlight the importance of incorporating demographic stochasticity into basic models of population genetics.
Parsons
Todd L
TL
Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
Quince
Christopher
C
Plotkin
Joshua B
JB
D000483:Alleles; D000818:Animals; D005787:Gene Frequency; D005828:Genetics, Population / Q000379:methods* / Q000706:statistics & numerical data; D006801:Humans; D008957:Models, Genetic; D009010:Monte Carlo Method; D009154:Mutation; D011156:Population Density; D011157:Population Dynamics; D012641:Selection, Genetic; D013269:Stochastic Processes
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