Laboratory of Genetics, University of Wisconsin-Madison, Madison, WI 53706, United States.
Evolution. 2023 Jun 29;77(7):1550-1563. doi: 10.1093/evolut/qpad060.
Secondary contact between formerly isolated populations may result in hybrid breakdown, in which untested allelic combinations in hybrids are maladaptive and limit genetic exchange. Studying early-stage reproductive isolation may yield key insights into the genetic architectures and evolutionary forces underlying the first steps toward speciation. Here, we leverage the recent worldwide expansion of Drosophila melanogaster to test for hybrid breakdown between populations that diverged within the last 13,000 years. We found clear evidence for hybrid breakdown in male reproduction, but not female reproduction or viability, supporting the prediction that hybrid breakdown affects the heterogametic sex first. The frequency of non-reproducing F2 males varied among different crosses involving the same southern African and European populations, as did the qualitative effect of cross direction, implying a genetically variable basis of hybrid breakdown and a role for uniparentally inherited factors. The levels of breakdown observed in F2 males were not recapitulated in backcrossed individuals, consistent with the existence of incompatibilities with at least three partners. Thus, some of the very first steps toward reproductive isolation could involve incompatibilities with complex and variable genetic architectures. Collectively, our findings emphasize this system's potential for future studies on the genetic and organismal basis of early-stage reproductive isolation.
次级隔离可能导致杂种衰退，杂种中未经测试的等位基因组合是适应不良的，并限制遗传交换。研究早期生殖隔离可能会深入了解遗传结构和进化力量，这些力量是物种形成的第一步的基础。在这里，我们利用黑腹果蝇在最近的全球扩张，来检验过去 13000 年内分化的种群之间的杂种衰退。我们在雄性生殖方面发现了明显的杂种衰退证据，但在雌性生殖或活力方面没有发现，这支持了杂种衰退首先影响异配性别这一预测。涉及相同的南非和欧洲种群的不同杂交中，不繁殖的 F2 雄性的频率存在差异，交叉方向的定性影响也存在差异，这意味着杂种衰退的遗传基础存在可变性，并且与单亲遗传因素有关。在回交个体中没有重现 F2 雄性中观察到的衰退水平，这与与至少三个伴侣的不兼容性一致。因此，生殖隔离的最初步骤可能涉及与复杂和可变的遗传结构的不兼容性。总的来说，我们的研究结果强调了这个系统在未来研究早期生殖隔离的遗传和机体基础方面的潜力。
