Genetics of hybrid male sterility among strains and species in the Drosophila pseudoobscura species group

Taxa in the early stages of speciation may bear intraspecific allelic variation at loci conferring barrier traits in hybrids such as hybrid sterility. Additionally, hybridization may spread alleles that confer barrier traits to other taxa. Historically, few studies examine within- and between-species variation at loci conferring reproductive isolation. Here, we test for allelic variation within Drosophila persimilis and within the Bogota subspecies of D. pseudoobscura at regions previously shown to contribute to hybrid male sterility. We also test whether D. persimilis and the USA subspecies of D. pseudoobscura share an allele conferring hybrid sterility in a D. pseudoobscura bogotana genetic background. All loci conferred similar hybrid sterility effects across all strains studied, though we detected some statistically significant quantitative effect variation among D. persimilis alleles of some hybrid incompatibility QTLs. We also detected allelism between D. persimilis and D. pseudoobscura USA at a 2nd chromosome hybrid sterility QTL. We hypothesize that either the QTL is ancestral in D. persimilis and D. pseudoobscura USA and lost in D. pseudoobscura bogotana, or gene flow transferred the QTL from D. persimilis to D. pseudoobscura USA. We discuss our findings in the context of population features that may contribute to variation in hybrid incompatibilities.

处于物种形成早期阶段的类群，其携带可导致杂种（如雄性杂种不育）相关生殖障碍性状的基因位点上，可能存在种内等位基因变异。此外，杂交作用可将携带障碍性状的等位基因扩散至其他类群。长期以来，针对与生殖隔离相关的基因位点开展种内与种间变异分析的研究相对较少。本研究针对此前已被证实可引发雄性杂种不育的基因组区域，分别检测了拟暗果蝇（Drosophila persimilis）以及伪暗果蝇（D. pseudoobscura）波哥大亚种内部的等位基因变异情况。同时，我们还检验了拟暗果蝇与伪暗果蝇美国亚种，在伪暗果蝇波哥大亚种的遗传背景下，是否共享可导致杂种不育的等位基因。尽管我们在部分杂种不相容性数量性状位点（Quantitative Trait Locus, QTL）的拟暗果蝇等位基因间，检测到了具有统计学显著性的数量效应差异，但所有被测菌株对应的基因位点均表现出相似的杂种不育效应。此外，我们在2号染色体的杂种不育QTL区域，检测到拟暗果蝇与伪暗果蝇美国亚种共享同一等位基因。我们提出两种假说：其一，该QTL在拟暗果蝇与伪暗果蝇美国亚种中均为祖先型等位基因，而在伪暗果蝇波哥大亚种中发生了丢失；其二，存在基因流将该QTL从拟暗果蝇转移至伪暗果蝇美国亚种。最后，我们结合可能影响杂种不相容性变异的种群特征，对本研究的发现展开了讨论。