Data from: Gametic selection, developmental trajectories, and extrinsic heterogeneity in Haldane's rule

Deciphering the genetic and developmental causes of the disproportionate rarity, inviability and sterility of hybrid males, Haldane's rule, is important for understanding the evolution of reproductive isolation between species. Moreover, extrinsic and pre-zygotic factors can contribute to the magnitude of intrinsic isolation experienced between species with partial reproductive compatibility. Here we use the nematodes Caenorhabditis briggsae and C. nigoni to quantify the sensitivity of hybrid male viability to extrinsic temperature and developmental timing, and test for a role of mito-nuclear incompatibility as a genetic cause. We demonstrate that hybrid male inviability manifests almost entirely as embryonic, not larval, arrest and is maximal at the lowest rearing temperatures, indicating an intrinsic-by-extrinsic interaction to hybrid inviability. Crosses using mitochondrial substitution strains that have reciprocally introgressed mitochondrial and nuclear genomes show that mito-nuclear incompatibility is not a dominant contributor to post-zygotic isolation and does not drive Haldane's rule in this system. Crosses also reveal that competitive superiority of X-bearing sperm provides a novel means by which post-mating pre-zygotic factors exacerbate the rarity of hybrid males. These findings highlight the important roles of gametic, developmental, and extrinsic factors in modulating the manifestation of Haldane's rule.

解析杂种雄性不成比例的稀有性、致死性与不育性的遗传与发育成因——即霍尔丹法则（Haldane's rule）——对于理解物种间生殖隔离的演化具有重要意义。此外，外源性与合子前因素可影响具有部分生殖兼容性的物种间所经历的内在隔离强度。本研究以布氏隐杆线虫（Caenorhabditis briggsae）与尼氏隐杆线虫（C. nigoni）为实验对象，量化杂种雄性生存力对外源温度与发育时序的敏感性，并检验线粒体-核基因组不兼容性（mito-nuclear incompatibility）作为遗传成因的作用。我们证实，杂种雄性致死性几乎完全表现为胚胎期而非幼虫期发育停滞，且在最低饲养温度下达到峰值，表明杂种致死存在内在-外源交互作用。使用相互导入线粒体与核基因组的线粒体替换菌株开展的杂交实验显示，线粒体-核基因组不兼容性并非合子后生殖隔离的主要贡献因素，也未在该系统中驱动霍尔丹法则。杂交实验还揭示，携带X染色体的精子的竞争优势，是一种全新途径，可通过交配后合子前因素加剧杂种雄性的稀有性。这些发现凸显了配子、发育与外源因素在调控霍尔丹法则表现形式中的重要作用。