九刺鱼小种群与大海域种群的重组率与连锁选择效率比较
Recombination rate and efficiency of linked selection in small and large stickleback populations
研究以九刺鱼（Pungitius pungitius）为对象，比较了4个小型淡水种群（平均N e ≈ 7,096）与4个大型海洋种群（平均N e = 376,828）的基因组重组率与连锁选择效率。除最小的淡水种群外，各群体核苷酸多样性（π）与重组率均呈正相关，提示连锁选择普遍存在，且在控制GC/CpG含量与基因密度变异后依然成立。淡水与海洋种群的平均重组率无差异，但N e 最小的淡水种群重组率显著升高。探索性GWAS提示重组率可能具有多基因基础。结果表明连锁选择在低重组区域降低π，尤其在大种群中作用明显，并支持小型淡水种群可能演化出高于其海洋祖先的重组率这一理论预测。
来源：PLOS Genetics · journals.plos.org
by Hongbo Wang, Chaowei Zhang, Kerry Reid, Juha Merilä
Population genetic theory predicts that natural selection will be more efficient in large than small populations because genetic drift reduces the efficiency of selection in small populations. Small populations adapting to new environments can also be expected to evolve higher recombination rates to facilitate adaptation as well as to dissociate and purge harmful mutations. We tested these hypotheses (1) by investigating differences in the strength of association between nucleotide diversity (π) and recombination rate across the genomes of nine-spined sticklebacks (Pungitius pungitius) from four small freshwater (mean Ne ≈ 7 096) and four large marine (mean Ne = 376 828) populations, as well as (2) by comparing recombination rates between small and large populations using population specific linkage maps. We found the predicted positive correlation of π with recombination rate from all but the smallest freshwater populations, suggesting prevalent linked selection even after accounting for variation in GC/CpG content, and gene density. Mean recombination rates did not differ between freshwater and marine populations, except that the smallest Ne freshwater population exhibited significantly elevated recombination rate. Exploratory GWAS analyses suggested a possible polygenic basis for recombination rate. These results suggest an important role for linked selection in reducing π in low recombination regions especially in large populations. Moreover, as predicted by theory, at least one of the small freshwater populations appears to have evolved a higher recombination rate than its marine ancestors.