School of Biological Sciences, University of Bristol, Bristol, United Kingdom.
Mol Biol Evol. 2012 Jan;29(1):195-206. doi: 10.1093/molbev/msr183. Epub 2011 Nov 22.
Does hybridization play a broad innovative role in evolution? Many studies have shown hybrid origins of individual species, particularly in major adaptive radiations, but this may be a consequence, rather than a cause, of the existence of many closely related species. Cases of hybridization in the early stages of major adaptive radiations are comparatively rare. Here, we report phylogenetic evidence for ancient introgression between distinct lineages of the species-rich Lake Malawi haplochromine cichlid fishes. Mitochondrial DNA (mtDNA) sequences indicated surprisingly close relationships between the shallow-water rocky habitat "Mbuna" species and a group of dark-adapted "Deep-Benthic" species specialized for feeding in low-light conditions (dawn/dusk, under overhangs, and deep water). By contrast, analyses of nuclear amplified fragment length polymorphism data demonstrated that these Deep-Benthic cichlids were more closely related to shallow water "Shallow-Benthic" soft-sediment feeders, a group that shares similar head and body morphology. A coalescent-based computer simulation indicated that the mtDNA similarity of rocky habitat Mbuna species and dark-adapted Deep-Benthic species was due to hybridization rather than incomplete lineage sorting. Comparisons of morphology indicated that some Deep-Benthic species possessed novel morphology not present in other Lake Malawi species groups. Thus, these analyses support the hypothesis that ancient hybridization occurred within the Lake Malawi cichlid radiation, that the event occurred before the radiation of a species group adapted to low-light benthic habitats, and that this group went on to dominate the deep-water regions of Lake Malawi. The results of this study contribute to a growing literature consistent with a creative role of hybridization in the evolution of species diversity and adaptive radiations.
杂交在进化中是否发挥了广泛的创新性作用？许多研究表明，杂交是个别物种的起源，特别是在主要的适应性辐射中，但这可能是存在许多密切相关物种的结果，而不是原因。在主要适应性辐射的早期阶段，杂交的情况相对较少。在这里，我们报告了在物种丰富的马拉维湖哈普洛林慈鲷鱼类的不同谱系之间存在古老的基因渗入的系统发育证据。线粒体 DNA（mtDNA）序列表明，浅水区的岩石生境“Mbuna”物种与一组适应低光条件（黎明/黄昏、悬垂下和深水）觅食的深色适应“深底栖”物种之间存在惊人的密切关系。相比之下，对核扩增片段长度多态性数据的分析表明，这些深底栖慈鲷与浅水区的“浅底栖”软底食者更为密切相关，这一组具有相似的头部和身体形态。基于合并的计算机模拟表明，岩石生境 Mbuna 物种和深色适应深底栖物种的 mtDNA 相似性是由于杂交而不是不完全谱系分选造成的。形态比较表明，一些深底栖物种具有其他马拉维湖物种组中不存在的新形态。因此，这些分析支持了以下假说：古老的杂交发生在马拉维湖慈鲷辐射内，该事件发生在适应低光底栖生境的物种组辐射之前，并且该组继续主导马拉维湖的深水区域。本研究的结果有助于越来越多的文献一致认为杂交在物种多样性和适应性辐射的进化中发挥了创造性作用。
