Sytsma Kenneth J, Schaal Barbara A
Department of Biology, Washington University, St. Louis, MO, 63130.
Evolution. 1985 May;39(3):594-608. doi: 10.1111/j.1558-5646.1985.tb00397.x.
The well-delimited and evolutionary interesting tropical shrub group, the Lisianthius skinneri (Gentianaceae) species complex, was analyzed for variation in nuclear ribosomal DNA and chloroplast DNA by restriction endonuclease fragment analysis. A most parsimonious tree using variations in both DNAs was constructed for seven populations in the group by including an appropriate outgroup. This phylogeny is significantly more compatible with the DNA data than most, but not all, less parsimonious phylogenies. At least two distinct lineages have independently evolved geographically restricted, cloud forest species from the putative ancestral, widespread, and lower elevation L. skinneri. Lisianthius skinneri itself is shown to be paraphyletic with populations derived separately from the two distinct lineages. Except for a switch in the placement of two populations, this DNA-based phylogeny is congruent with an isozyme-based Wagner network depicting relationships in the species complex. Relative rates of divergence, in terms of nuclear ribosomal DNA, chloroplast DNA, isozymes, and morphology, differ markedly within and between lineages. The non-transcribed spacer region of ribosomal DNA is shown to evolve in a manner that is not in accord with a molecular clock hypothesis. Small population sizes, restricted and isolated nature of populations, and probable founder events are suggested as instrumental in causing this lack of concerted divergence within and between lineages of the L. skinneri species complex.
对界限分明且具有进化研究意义的热带灌木类群——斯氏萼距花（龙胆科）物种复合体，通过限制性内切酶片段分析研究了其核糖体DNA和叶绿体DNA的变异情况。通过纳入合适的外类群，利用这两种DNA的变异构建了该类群中七个种群的最简系统树。与大多数（但并非全部）更复杂的系统发育树相比，这个系统发育树与DNA数据的兼容性明显更高。至少有两个不同的谱系独立地从假定的祖先、分布广泛且海拔较低的斯氏萼距花进化出了地理分布受限的云雾林物种。研究表明，斯氏萼距花本身是并系的，其种群分别源自两个不同的谱系。除了两个种群的位置发生了互换外，这个基于DNA的系统发育树与描绘该物种复合体关系的基于同工酶的瓦格纳网络是一致的。在谱系内部和谱系之间，核糖体DNA、叶绿体DNA、同工酶和形态学方面的相对分化速率存在显著差异。核糖体DNA的非转录间隔区的进化方式不符合分子钟假说。种群规模小、种群的受限和隔离性质以及可能的奠基者事件被认为是导致斯氏萼距花物种复合体谱系内部和之间缺乏协同分化的重要因素。
