Why isn’t diversity proportional to population size?
Natural selection via hitchhiking and background selection constrains neutral diversity, especially in species with larger census sizes.
Source
Natural selection constrains neutral diversity across a wide range of species
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Why isn’t diversity proportional to population size?
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How do HH and BGS affect linked neutrals?
positive selection via HH and negative selection via BGS purge linked neutral mutations, the operation of natural selection affects patterns of neutral genetic variation at linked sites across the genome.
What pattern do larger-Nc species show?
species with larger Nc display a stronger correlation between neutral polymorphism and recombination rate, and that natural selection removes disproportionately more linked neutral variation from species with larger populations.
What they did
Compared polymorphism–recombination relationships across many species to test how selection shapes linked neutral diversity relative to census size (Nc).
What they found
Species with larger Nc show stronger correlation between neutral polymorphism and recombination rate, indicating a larger role for selection in shaping genome-wide diversity.
The limits
What it doesn't show
Cryptic population structure can still influence variation patterns; mechanisms are inferred comparatively.
Key terms
- Neutral diversity
- Genetic variation not directly under selection.
- Genetic hitchhiking (HH)
- Linked neutral variants swept with beneficial alleles.
- Background selection (BGS)
- Removal of linked neutrals by purifying selection.
- Recombination rate
- Frequency of crossing-over affecting linkage.
- Census size (Nc)
- Actual number of individuals in a species.
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Larger Nc species show:
Common questions
What purges linked neutrals?
Positive selection (HH) and negative selection (BGS).
Who shows stronger poly–recomb correlation?
Species with larger Nc.
Lewontin’s puzzle?
Diversity varies less than census size predicts.
Caveat?
Population structure can confound patterns.
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