Adaptive radiations have proven important for understanding the mechanisms and processes underlying biological diversity. The convergence of form and function, as well as admixture and adaptive introgression, are common in adaptive radiations. However, distinguishing between these two scenarios remains a challenge for evolutionary research. The Midas cichlid species complex (Amphilophus spp.) is a prime example of adaptive radiation, with phenotypic diversification occurring at various stages of genetic differentiation. One species, A. labiatus, has large fleshy lips, is associated with rocky lake substrates, and occurs patchily within Lakes Nicaragua and Managua. By contrast, the similar, but thin-lipped, congener, A. citrinellus, is more common and widespread. We investigated the evolutionary history of the large-lipped form, specifically regarding whether the trait has evolved independently in both lakes from ancestral thin-lipped populations, or via dispersal and/or admixture events. We collected samples from distinct locations in both lakes, and assessed differences in morphology and ecology. Using RAD-seq, we genotyped thousands of SNPs to measure population structure and divergence, demographic history, and admixture. We found significant between-species differences in ecology and morphology, local intraspecific differences in body shape and trophic traits, but only limited intraspecific variation in lip shape. Despite clear ecological differences, our genomic approach uncovered pervasive admixture between the species and low genomic differentiation, with species within lakes being genetically more similar than species between lakes. Taken together, our results suggest a single origin of large-lips, followed by pervasive admixture and adaptive introgression, with morphology being driven by local ecological opportunities, despite ongoing gene-flow.

中文翻译：

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普遍的混合物和大唇形式在慈鲷鱼辐射中的传播

适应性辐射已被证明对于理解生物多样性的机制和过程很重要。形式和功能的融合，以及混合和适应性基因渗入，在适应性辐射中很常见。然而，区分这两种情况仍然是进化研究的挑战。Midas cichlid 物种复合体 ( Amphilophus spp.) 是适应性辐射的一个典型例子，其表型多样化发生在遗传分化的不同阶段。一种，A . labiatus有大的肉质嘴唇，与岩石湖泊基质有关，并在尼加拉瓜湖和马那瓜湖中零星分布。相比之下，相似但薄唇的同源物A。黄鳝, 更为普遍和普遍。我们调查了大唇型的进化历史，特别是关于该特征是否在两个湖泊中独立于祖先的薄唇种群进化，或通过扩散和/或混合事件。我们从两个湖泊的不同位置收集样本，并评估了形态和生态学的差异。使用 RAD-seq，我们对数千个 SNP 进行基因分型，以测量种群结构和差异、人口统计历史和混合。我们发现生态学和形态学存在显着的种间差异，体型和营养性状的局部种内差异，但唇形的种内差异有限。尽管存在明显的生态差异，但我们的基因组方法揭示了物种之间普遍存在的混合物和低基因组分化，湖泊内的物种在遗传上比湖泊之间的物种更相似。总之，我们的结果表明大唇的单一起源，其次是普遍的混合和适应性渐渗，尽管基因流动正在进行，但形态受到当地生态机会的驱动。