Data from: Fine‐scale geographic patterns of gene flow and reproductive character displacement in drosophila subquinaria and d. recens

When two species are incompletely isolated, strengthening premating isolation barriers in response to the production of low fitness hybrids may complete the speciation process. Here we use the sister species Drosophila subquinaria and D. recens to study the conditions under which this reinforcement of species boundaries occurs in natural populations. We first extend the region of known sympatry between these species, and then we conduct a fine-scale geographic survey of mate discrimination coupled with estimates of gene flow within and admixture between species. Within D. subquinaria reinforcement is extremely effective: we find variation in mate discrimination both against D. recens males as well as against conspecific allopatric males on the scale of a few kilometers and in the face of gene flow both from conspecific populations and introgression from D. recens. In D. recens we do not find evidence for increased mate discrimination in sympatry, even where D. recens is rare, consistent with substantial gene flow throughout the species’ range. Finally, we find that introgression between species is asymmetric, with more from D. recens into D. subquinaria than vice versa. Within each species admixture is highest in the geographic region where it is rare relative to the other species, suggesting that when hybrids are produced they are of low fitness. In sum, reinforcement within D. subquinaria is effective at maintaining species boundaries, but even when reinforcing selection is strong it may not always result in a pattern of strong reproductive character displacement due to variation in the frequency of hybridization and gene flow from neighboring populations.

当两个物种的生殖隔离不完全时，针对低适合度杂交后代的产生而强化交配前隔离（premating isolation）屏障，可推动物种形成过程的完成。本研究以姊妹种亚奎果蝇（Drosophila subquinaria）和莱茵果蝇（D. recens）为研究对象，探究自然种群中物种边界生殖强化（reinforcement）现象发生的条件。我们首先拓展了已知的两物种同域分布（sympatry）范围，随后开展了精细尺度地理调查，对配偶识别（mate discrimination）进行分析，并结合物种内部基因流（gene flow）与物种间基因混合（admixture）程度的估算。在亚奎果蝇种群中，物种边界生殖强化效果极为显著：我们观测到，即便面临来自同种种群的基因流以及莱茵果蝇的基因渗入（introgression），在数公里的尺度上，其针对莱茵果蝇雄性以及异域分布同种雄性的配偶识别均存在变异。而在莱茵果蝇种群中，我们未发现同域分布种群配偶识别增强的证据，即便在莱茵果蝇种群数量稀少的区域亦是如此，这与该物种整个分布范围内存在大量基因流的结论一致。最后，我们发现两物种间的基因渗入存在不对称性：莱茵果蝇向亚奎果蝇的基因渗入量远高于反向渗入。在每个物种中，当某一区域内该物种种群数量相对于另一物种较为稀少时，其基因混合程度最高，这表明当杂交后代产生时，其适合度较低。综上，亚奎果蝇体内的物种边界生殖强化可有效维持物种隔离，但即便强化选择作用强烈，由于杂交频率以及邻种群基因流的差异，该过程未必总能形成显著的生殖特征置换（reproductive character displacement）格局。