Experimental introgression in Drosophila: Asymmetric postzygotic isolation associated with chromosomal inversions and an incompatibility locus on the X chromosome

Interspecific gene flow (introgression) is an important source of new genetic variation, but selection against it can reinforce reproductive barriers between interbreeding species. We used an experimental approach to trace the role of chromosomal inversions and incompatibility genes in preventing introgression between two partly sympatric Drosophila virilis group species, D. flavomontana and D. montana. We backcrossed F1 hybrid females from a cross between D. flavomontana female and D. montana male with the males of the parental species for two generations and sequenced pools of parental strains and their reciprocal 2nd generation backcross (BC2mon and BC2fla) females. Contrasting the observed amount of introgression (mean hybrid index, HI) in BC2 female pools along the genome to simulations under different scenarios allowed us to identify chromosomal regions of restricted and increased introgression. We found no deviation from the HI expected under a neutral null model for any chromoso..., ,

种间基因流（introgression）是新遗传变异的重要来源，但针对其的选择可强化异种交配物种间的生殖隔离屏障。本研究采用实验方法，探究染色体倒位与不相容基因在阻止两种部分同域分布的维氏果蝇组（Drosophila virilis group）物种——黄山果蝇（D. flavomontana）与山果蝇（D. montana）——之间基因渐渗的作用。我们将黄山果蝇雌蝇与山果蝇雄蝇杂交获得的F1杂交雌蝇，与亲本物种的雄蝇进行两代回交，并对亲本菌株及其双向第二代回交（BC2mon与BC2fla）雌蝇的混合样本进行测序。将BC2雌蝇混合样本全基因组中观测到的渐渗量（平均杂交指数，HI）与不同场景下的模拟结果进行对比，我们得以鉴定出渐渗受限与渐渗增加的染色体区域。我们发现，在中性零模型下，任何染色体的平均杂交指数（HI）均未出现与预期值不符的偏差……