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
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.
Flashcards
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Quiz yourself
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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