Recombination rate and efficiency of linked selection in small and large stickleback populations.

Recombination rate is positively correlated with nucleotide diversity (π) across nine-spined stickleback genomes, indicating prevalent linked selection, with the smallest freshwater population showing significantly elevated recombination.

• Why it matters: Theory predicts selection is less efficient in small populations due to drift, and adaptation may be aided by higher recombination; linked selection should shape diversity especially in low-recombination regions.
• What they did: The study compared π–recombination associations across genomes of Pungitius pungitius from four small freshwater (mean Ne ≈ 7 096) and four large marine (mean Ne = 376 828) populations, and used population-specific linkage maps to contrast recombination rates.
• The result: Mean recombination rates did not differ between freshwater and marine populations except in the smallest freshwater population, and results suggest linked selection reduces π in low-recombination regions, with at least one small freshwater population evolving higher recombination than marine ancestors.