Genetic divergence of populations in the presence of gene flow is a central theme in speciation research. Theory predicts that divergence can happen with full range overlap – in sympatry – driven by ecological factors, but there are few empirical examples of how ecologically divergent selection can overcome gene flow and lead to reproductive isolation. In the marine midge Clunio marinus (Diptera: Chironomidae) reproduction is ecologically restricted to the time of the lowest tides, which is ensured through accurate control of development and adult emergence by circalunar and circadian clocks. As tidal regimes differ along the coastline, locally adapted timing strains of C. marinus are found in different sites across Europe. At the same time, ecologically suitable low tides occur at both full and new moon and twice a day, providing C. marinus with four nonoverlapping temporal niches at every geographic location. Along the coast of Brittany, which is characterized by a steep gradient in timing of the tides, we found an unusually large number of differentially adapted timing strains, and the first known instances of sympatric C. marinus strains occupying divergent temporal niches. Analysis of mitochondrial genotypes suggests that these timing strains originated from a single recent colonization event. Nuclear genotypes show strong gene flow, sympatric timing strains being the least differentiated. Even when sympatric strains exist in nonoverlapping temporal niches, timing adaptations do not result in genome‐wide genetic divergence, suggesting timing adaptations are maintained by permanent ecological selection. This constitutes a model case for incipient ecological divergence with gene flow.

中文翻译：

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海洋昆虫Clunio marinus的定时菌株发散并持续存在基因流

存在基因流时种群的遗传差异是物种研究的中心主题。理论预测，在生态学因素的驱动下，在共交点范围内，可能发生全范围重叠，但是在生态差异选择中如何克服基因流并导致生殖隔离的经验例子很少。在海洋mid中（Cluio marinus）（双翅目：Chironomidae）在生态上仅限于潮汐最低的时间，这可以通过生物钟和生物钟的精确控制发育和成虫的出现来确保。由于沿海岸线的潮汐机制不同，因此，当地适应的C. marinus时间株在整个欧洲的不同地点都可以找到。同时，在满月和新月以及每天两次，都出现了生态上合适的低潮，从而为C. marinus在每个地理位置提供了四个不重叠的时空ni。沿着布列塔尼海岸，其特征是潮汐的时间梯度陡峭，我们发现了大量异常适应时间差的应变，以及同胞C.marinus的第一个已知实例株占据了不同的时空壁ni。线粒体基因型的分析表明，这些定时菌株起源于最近的一次定殖事件。核基因型显示出强大的基因流，同胞时间株差异最小。即使同属菌株存在于不重叠的时空生态位中，时序适应也不会导致全基因组遗传差异，这表明时序适应通过永久的生态选择得以维持。这构成了具有基因流的初始生态差异的模型案例。