Introgression patterns between divergent lineages are often characterized by asymmetry in the direction and among-marker variation in the extent of gene flow, and therefore inform on the mechanisms involved in differentiation and speciation. In the present study, we test the hypothesis that unidirectional introgression between two phenotypically and genetically distinct lineages of the littoral, rock-dwelling cichlid fish Tropheus moorii across a wide sandy bay is linked to observed differences in mate preferences between the two lineages. This hypothesis predicts bi-directional nuclear gene flow and was rejected by congruent patterns of introgression in mtDNA, AFLP and microsatellite markers, with admixture confined to the populations west of the bay. This pattern can be explained on the basis of habitat changes in the course of lake level fluctuations, which first facilitated the development of a symmetric admixture zone including the area corresponding to the present sand bay and then shaped asymmetry by causing local extinctions and cessation of gene flow when this area became once more inhabitable. This conforms with previous assumptions that habitat dynamics are a primary determinant of population-level evolution in Tropheus. In this respect, Tropheus may be representative of species whose preferred habitat is subject to frequent re-structuring.

中文翻译：

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过去的湖岸动态解释了目前跨越栖息地屏障的单向渐渗模式

不同谱系之间的基因渗入模式通常以基因流动程度的方向不对称和标记间变异为特征，因此可以了解分化和物种形成所涉及的机制。在本研究中，我们检验了这样一个假设，即在广阔的沙湾中，生活在岩石上的滨海慈鲷鱼 Tropheus moorii 的两个表型和遗传上不同的谱系之间的单向渗入与观察到的两个谱系之间配偶偏好的差异有关。这一假设预测了双向核基因流动，但被 mtDNA、AFLP 和微卫星标记中一致的基因渗入模式拒绝，混合物仅限于海湾以西的种群。这种模式可以根据湖水位波动过程中栖息地的变化来解释，这首先促进了包括与现在沙湾相对应的区域在内的对称混合带的发展，然后通过导致局部灭绝和基因停止而形成不对称当这个区域再次变得适合居住时流动。这符合先前的假设，即栖息地动态是 Tropheus 种群水平进化的主要决定因素。在这方面，Tropheus 可能是其首选栖息地频繁重组的物种的代表。这首先促进了包括与当前沙湾相对应的区域在内的对称混合带的发展，然后当该区域再次变得可居住时，通过导致局部灭绝和基因流动停止而形成不对称。这符合先前的假设，即栖息地动态是 Tropheus 种群水平进化的主要决定因素。在这方面，Tropheus 可能是其首选栖息地频繁重组的物种的代表。这首先促进了包括与当前沙湾相对应的区域在内的对称混合带的发展，然后当该区域再次变得可居住时，通过导致局部灭绝和基因流动停止而形成不对称。这符合先前的假设，即栖息地动态是 Tropheus 种群水平进化的主要决定因素。在这方面，Tropheus 可能是其首选栖息地频繁重组的物种的代表。