Recombination rate variation shapes barriers to introgression across butterfly genomes

Hybridisation and introgression can dramatically alter the relationships among groups of species, leading to phylogenetic discordance across the genome and between populations. Introgression can also erode species differences over time, but selection against introgression at certain loci acts to maintain post-mating species barriers. Theory predicts that species barriers made up of many loci throughout the genome should lead to a broad correlation between introgression and recombination rate, which determines the extent to which selection on deleterious foreign alleles will affect neutral alleles at physically linked loci. Here we describe the variation in genealogical relationships across the genome among three species of Heliconius butterflies: H. melpomene, H. cydno and H. timareta, using whole genomes of 92 individuals, and ask whether this variation can be explained by heterogeneous barriers to introgression. We find that species relationships vary predictably at the chromosomal s...杂交与基因渐渗（introgression）可显著改变物种类群间的演化关系，引发全基因组乃至种群间的系统发育冲突（phylogenetic discordance）。基因渐渗还会随时间推移逐步削弱物种间的分化差异，但特定基因座上针对渐渗的选择作用，得以维持交配后物种屏障（post-mating species barriers）。理论预测，由基因组内众多基因座构成的物种屏障，应会使基因渐渗与重组率（recombination rate）之间呈现广泛的相关性：重组率决定了针对有害外来等位基因（deleterious foreign alleles）的选择，能够在多大程度上影响物理连锁位点（physically linked loci）上的中性等位基因（neutral alleles）。本研究依托92个个体的全基因组（whole genomes）数据，解析了3种袖蝶属（Heliconius）蝴蝶——H. melpomene、H. cydno与H. timareta——的全基因组系谱关系变异，并探究该变异是否可由异质性的渐渗屏障加以解释。研究发现，物种间的演化关系在染色体水平上呈现可预测的差异……