Hollocher H, Hatcher J L, Dyreson E G
Department of Ecology and Evolutionary Biology, Princeton University, New Jersey 08544, USA.
Evolution. 2000 Dec;54(6):2046-56. doi: 10.1111/j.0014-3820.2000.tb01248.x.
The Drosophila dunni subgroup displays a nearly perfect latitudinal cline in abdominal pigmentation that likely resulted from selective forces acting in the habitat of each species during speciation. Here we characterize the nature of this clinal variation by developing a quantitative measure to assess variation in abdominal pigmentation within and between the D. dunni subgroup species. Using discriminant analysis, we confirm the existence of a cline and find that our quantitative measure of pigmentation distinguishes each of the species with singular efficacy. We then combine our quantitative phenotypic analysis of pigmentation with the phylogeny of the D. dunni subgroup species and map the species relationships into the three-dimensional morphological space defined by our pigmentation measures. In this manner, we can visualize how the species have traversed the morphological pigmentation space during the course of speciation. Our analysis reveals that natural selection has caused overall intensity of pigmentation among the northernmost species of the cline to converge. Along with this convergence in phenotype has been a relaxation in expression of sexual dimorphism in these species, indicating a possible shift in the relative intensity of natural and sexual selection. Our analysis indicates an accelerated rate of change in pigmentation for the darkest species in addition to this species evolving a novel abdominal pigmentation trait.
果蝇邓氏亚组在腹部色素沉着方面呈现出近乎完美的纬度渐变群，这可能是物种形成过程中作用于每个物种栖息地的选择力所致。在此，我们通过开发一种定量方法来评估邓氏果蝇亚组物种内部和之间腹部色素沉着的变化，从而描述这种渐变变异的本质。通过判别分析，我们证实了渐变群的存在，并发现我们对色素沉着的定量测量能以独特的效力区分每个物种。然后，我们将色素沉着的定量表型分析与邓氏果蝇亚组物种的系统发育相结合，并将物种关系映射到由我们的色素沉着测量所定义的三维形态空间中。通过这种方式，我们可以直观地看到物种在物种形成过程中是如何穿越形态色素沉着空间的。我们的分析表明，自然选择导致渐变群最北部物种的色素沉着总体强度趋同。伴随着这种表型趋同，这些物种的性二态性表达有所放松，这表明自然选择和性选择的相对强度可能发生了转变。我们的分析表明，除了该物种进化出一种新的腹部色素沉着特征外，最黑的物种在色素沉着方面的变化速度加快。
