Samples from subdivided populations yield biased estimates of effective size that overestimate the rate of loss of genetic variation.
Bottom Line: Many empirical studies estimating effective population size apply the temporal method that provides an estimate of the variance effective size through the amount of temporal allele frequency change under the assumption that the study population is completely isolated.We studied how gene flow affects estimates of effective size obtained by the temporal method when sampling from a population system and provide analytical expressions for the expected estimate under an island model of migration.This phenomenon might partially explain the frequently reported unexpectedly low effective population sizes of marine populations that have raised concern regarding the genetic vulnerability of even exceptionally large populations.
Affiliation: Division of Population Genetics, Department of Zoology, Stockholm University, SE-106 91, Stockholm, Sweden.Show MeSH
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Mentions: The difficulties associated with obtaining a reasonably unbiased estimate of global effective size (Fig.1b) have implications for assessments of genetic vulnerability and loss of genetic variation. Under an island model, the rate of loss of heterozygosity in a local subpopulation is determined by the effective size of the global population rather than that of the local one. The expected change of heterozygosity in a local subpopulation (HS) and in the global one as a whole (HT) can be obtained directly from recursion equations for gene identity (Nei 1975; Li 1976; Ryman & Leimar 2008). As an example, Fig.5 depicts the expected change of GST (equivalent to FST), HS and HT over the first t = 500 generations for a population system similar to that in Fig.2 with s = 10 partially isolated subpopulations of effective size N = 50 and a migration rate of m = 0.01 in the absence of mutation (the figure was produced using eqn 2–3 of Ryman & Leimar 2008).
Affiliation: Division of Population Genetics, Department of Zoology, Stockholm University, SE-106 91, Stockholm, Sweden.