Brisson Jennifer A, Wilder Jason, Hollocher Hope
Department of Biology, Washington University, St. Louis, Missouri 63130, USA.
Evolution. 2006 Jun;60(6):1228-41.
Phenotypic variability is the engine that drives future diversification with the expectation that polymorphic ancestors give rise to descendants harboring a subset of the ancestral variation. Here we examine evolutionary transitions from polymorphism to monomorphism in a visually striking New World radiation of fruit flies, the Drosophila cardini group. This group is distributed across the Americas and the Caribbean islands and exhibits a wide spectrum of abdominal pigmentation variation. Specifically, the D. dunni subgroup consists of Caribbean island endemics, each of which is monomorphic for its pigmentation pattern, with an interspecific cline of pigmentation across the islands. The D. cardini subgroup consists of American continental species with wide-ranging distributions and intraspecifically variable abdominal pigmentation. We determined the phylogeny of 18 species and subspecies using three nuclear and three mitochondrial regions analyzed with maximum parsimony, maximum likelihood, and Bayesian methods. The topology produced from a combined dataset exhibited high support values at all nodes, and differed from earlier phylogenetic hypotheses based on polytene chromosome inversion patterns and isozyme data. We find that the D. dunni subgroup species, with the exception of D. belladunni, are derived from a single source not of direct South American origin and their dispersal across the islands of the Caribbean does not follow a simple stepping-stone model. Morphological changes in pigmentation across the island species are incongruent with the colonization history of the group indicating that natural selection may have played a role in the determination of this character. Finally, we demonstrate that monomorphic species have arisen independently from polymorphic ancestors two to three times.
表型变异性是推动未来多样化的引擎，预期多态性祖先会产生携带部分祖先变异的后代。在这里，我们研究了果蝇卡迪尼组（Drosophila cardini group）这一在视觉上引人注目的新大陆果蝇辐射中从多态性到单态性的进化转变。该组分布于美洲和加勒比群岛，呈现出广泛的腹部色素沉着变异。具体而言，邓氏果蝇亚组（D. dunni subgroup）由加勒比群岛特有种组成，每个特有种的色素沉着模式都是单态的，且各岛屿间存在色素沉着的种间渐变群。卡迪尼果蝇亚组（D. cardini subgroup）由分布广泛且种内腹部色素沉着可变的美洲大陆物种组成。我们使用三个核区域和三个线粒体区域，通过最大简约法、最大似然法和贝叶斯方法分析，确定了18个物种和亚种的系统发育。由合并数据集产生的拓扑结构在所有节点处都表现出高支持值，并且与基于多线染色体倒位模式和同工酶数据的早期系统发育假设不同。我们发现，除贝拉邓氏果蝇（D. belladunni）外，邓氏果蝇亚组的物种都源自单一来源，并非直接来自南美洲，它们在加勒比群岛的扩散并不遵循简单的踏脚石模型。各岛屿物种色素沉着的形态变化与该组的殖民历史不一致，这表明自然选择可能在这一性状的决定中发挥了作用。最后，我们证明单态物种已从多态祖先独立出现了两到三次。
