Limits to the rate of adaptive substitution in sexual populations.
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Heritable variance v in log fitness due to unlinked loci reduces Λ by e⁻⁴(v) under polygamy and e⁻⁸ (v) under monogamy.We also consider the effect of sweeps on neutral diversity and show that, while even occasional sweeps can greatly reduce neutral diversity, this effect saturates as sweeps become more common-diversity can be maintained even in populations experiencing very strong interference.Our results indicate that for some organisms the rate of adaptive substitution may be primarily recombination-limited, depending only weakly on the mutation supply and the strength of selection.
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Affiliation: Institute of Science and Technology Austria, Klosterneuburg, Austria. dbw@ist.ac.at
ABSTRACT In large populations, many beneficial mutations may be simultaneously available and may compete with one another, slowing adaptation. By finding the probability of fixation of a favorable allele in a simple model of a haploid sexual population, we find limits to the rate of adaptive substitution, Λ, that depend on simple parameter combinations. When variance in fitness is low and linkage is loose, the baseline rate of substitution is Λ₀ = 2NU Related in: MedlinePlus |
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Mentions: Figure 8 shows that alleles with small selective advantages are much more affected by interference than those with large selective advantages. To understand this, consider the probability of fixation of an allele with advantage , , given the distribution of mutational effects. (For the exponential distribution we consider here, .) If the effects of multiple interfering sweeps are additive, then following the argument given in Text S4 , we can write the probability of fixation as(10)where the factor depends only on the ratio of the selective coefficients. Eq. (10) approaches 0 at some ; alleles with selection coefficients are nearly unaffected by interference, while those with lower are strongly affected. (Obviously, the Eq. (10) only applies to values of above this cutoff ; we discuss weakly-selected alleles below.) can be understood as the rate at which the focal allele is knocked back by interfering sweeps [79]. |
View Article: PubMed Central - PubMed
Affiliation: Institute of Science and Technology Austria, Klosterneuburg, Austria. dbw@ist.ac.at