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.解析杂交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，外在因素与合子前因素可影响部分生殖兼容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）为模型，量化杂交雄性存活率对外在培养温度与发育时序的敏感性，并检验线粒体-核不相容性（mito-nuclear incompatibility）是否为其遗传成因之一。我们证实，杂交雄性致死性几乎完全表现为胚胎阻滞而非幼虫阻滞，且在最低培养温度下致死效应最强，表明杂交致死存在内在-外在交互作用。利用携带相互渐渗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-核不相容性并非合子后生殖隔离的主要驱动因素，亦未在该体系中介导霍尔丹法则。杂交实验还揭示，携带X染色体的精子的竞争优势，是交配后合子前因素加剧杂交雄性稀有性的一种全新机制。本研究结果凸显了配子、发育与外在因素在调控霍尔丹法则表现形式中的重要作用。