Department of Fish Ecology and Evolution, Centre of Ecology, Evolution and Biogeochemistry, Eawag Swiss Federal Institute of Aquatic Science and Technology, Kastanienbaum, Switzerland.
Division of Aquatic Ecology and Evolution, Institute of Ecology and Evolution, University of Bern, Bern, Switzerland.
Evolution. 2024 Mar 26;78(4):652-664. doi: 10.1093/evolut/qpae007.
Intrinsic postzygotic hybrid incompatibilities are usually due to negative epistatic interactions between alleles from different parental genomes. While such incompatibilities are thought to be uncommon in speciation with gene flow, they may be important if such speciation results from a hybrid population. Here we aimed to test this idea in the endemic cichlid fishes of Lake Victoria. Hundreds of species have evolved within the lake in <15k years from hybrid progenitors. While the importance of prezygotic barriers to gene flow is well established in this system, the possible relevance of postzygotic genetic incompatibilities is unknown. We inferred the presence of negative epistatic interactions from systematic patterns of genotype ratio distortions in experimental crosses and wild samples. We then compared the positions of putative incompatibility loci to regions of high genetic differentiation between sympatric sister species and between members of clades that may have arisen in the early history of this radiation, and further determined if the loci showed fixed differences between the closest living relatives of the lineages ancestral to the hybrid progenitors. Overall, we find little evidence for a major role of intrinsic postzygotic incompatibilities in the Lake Victoria radiation. However, we find putative incompatibility loci significantly more often coinciding with islands of genetic differentiation between species that separated early in the radiation than between the younger sister species, consistent with the hypothesis that such variants segregated in the hybrid swarm and were sorted between species in the early speciation events.
内在的合子后杂种不亲和性通常是由于来自不同亲本体基因组的等位基因之间的负上位性相互作用。虽然在有基因流的物种形成中，这种不亲和性被认为不常见，但如果这种物种形成是由杂交种群引起的，它可能很重要。在这里，我们旨在检验这个想法在维多利亚湖的特有慈鲷鱼类中。在不到 15000 年的时间里，数百个物种从杂交后代中进化而来。虽然在这个系统中，前合子障碍对基因流的重要性已经得到很好的证实，但合子后遗传不兼容性的可能相关性尚不清楚。我们从实验杂交和野生样本中基因型比例扭曲的系统模式推断出负上位性相互作用的存在。然后，我们将假定的不兼容基因座的位置与近缘种之间的高遗传分化区域进行了比较，并进一步确定了这些基因座在与杂交祖先的最近亲缘关系之间是否存在固定差异。总的来说，我们几乎没有发现内在的合子后不兼容性在维多利亚湖辐射中起主要作用的证据。然而，我们发现假定的不兼容性基因座与辐射早期分离的物种之间的遗传分化岛屿的吻合程度显著高于与年轻近缘种之间的吻合程度，这与这样的变体在杂交群中分离并在早期的物种形成事件中在物种之间进行分类的假设是一致的。
