Wilson A B, Noack-Kunnmann K, Meyer A
Department of Biology, University of Konstanz, 78457 Konstanz, Germany.
Proc Biol Sci. 2000 Nov 7;267(1458):2133-41. doi: 10.1098/rspb.2000.1260.
The growing body of empirical evidence for sympatric speciation has been complemented by recent theoretical treatments that have identified evolutionary conditions conducive to speciation in sympatry. The Neotropical Midas cichlid (Amphilophus citrinellum) fits both of the key characteristics of these models, with strong assortative mating on the basis of a colour polymorphism coupled with trophic and ecological differentiation derived from a polymorphism in their pharyngeal jaws. We used microsatellite markers and a 480 bp fragment of the mitochondrial DNA control region to study four polymorphic populations of the Midas cichlid from three crater lakes and one large lake in Nicaragua in an investigation of incipient sympatric speciation. All populations were strongly genetically differentiated on the basis of geography. We identified strong genetic separation based on colour polymorphism for populations from Lake Nicaragua and one crater lake (Lake Apoyo), but failed to find significant genetic structuring based on trophic differences and ecological niche separation in any of the four populations studied. These data support the idea that sexual selection through assortative mating contributes more strongly or earlier during speciation in sympatry than ecological separation in these cichlids. The long-term persistence of divergent cichlid ecotypes (as measured by the percentage sequence divergence between populations) in Central American crater lakes, despite a lack of fixed genetic differentiation, differs strikingly from the patterns of extremely rapid speciation in the cichlids in Africa, including its crater lakes. It is unclear whether extrinsic environmental factors or intrinsic biological differences, e.g. in the degree of phenotypic plasticity, promote different mechanisms and thereby rates of speciation of cichlid fishes from the Old and New Worlds.
关于同域物种形成的实证证据越来越多，最近的理论研究也对其进行了补充，这些研究确定了有利于同域物种形成的进化条件。新热带地区的迈达斯丽鱼（Amphilophus citrinellum）符合这些模型的两个关键特征，即基于颜色多态性的强烈选型交配，以及源于咽颌多态性的营养和生态分化。我们使用微卫星标记和线粒体DNA控制区的一个480 bp片段，对来自尼加拉瓜三个火山口湖和一个大湖的四个多态性迈达斯丽鱼种群进行了研究，以调查初始同域物种形成。所有种群在地理基础上都有很强的遗传分化。我们发现，尼加拉瓜湖和一个火山口湖（阿波约湖）的种群基于颜色多态性存在强烈的遗传分离，但在所研究的四个种群中，均未发现基于营养差异和生态位分离的显著遗传结构。这些数据支持了这样一种观点，即在这些丽鱼的同域物种形成过程中，通过选型交配进行的性选择比生态隔离发挥了更强烈或更早的作用。尽管缺乏固定的遗传分化，但中美洲火山口湖中的不同丽鱼生态型（以种群间的序列差异百分比衡量）长期存在，这与非洲丽鱼（包括其火山口湖中的丽鱼）极其快速的物种形成模式形成了鲜明对比。目前尚不清楚外部环境因素或内在生物学差异，例如表型可塑性的程度，是否促进了不同的机制，从而导致了新旧世界丽鱼科鱼类不同的物种形成速率。
