Dissertation Research: The Role of Hybridization in the Evolution of Argyranthemum in Macaronesia

9902276詹森岛和格尔岑岛是研究进化过程的理想自然实验室。它们的孤立性、环境的可变性和容易确定的年龄，帮助了自达尔文以来的生物学家揭示进化变化背后的力量。自然杂交是植物和动物进化中潜在的主要力量，我们对自然杂交的理解已经通过对夏威夷和胡安费尔南德斯群岛物种的研究得到了很大的进展。在德克萨斯大学奥斯汀分校Robert K. Jansen博士的指导下，研究生Leslie Goertzen正在研究杂交在银菊属（菊科）植物进化中的作用。这一群只有在马卡罗西亚群岛（加那利群岛、马德拉群岛和萨瓦拉群岛）发现的24个物种是整个岛屿海拔带适应性辐射的一个壮观例子，它有许多特征，使它成为解决进化问题的模型系统。本研究将研究古渐渗的证据，以及当代物种接触的动态和后果。利用可变核DNA序列构建这些岛屿植物的系统发育框架，并将这些数据与母系遗传的叶绿体DNA进行统计比较。初步数据表明，两个数据集之间存在一些物种对的显著不一致，这提高了这些谱系在进化过程中出现渐渗杂交的可能性。当代杂交的具体情况将通过筛选自然和杂交群体的物种特异性核和叶绿体遗传标记进行检查。这将使种间基因流动的方向和程度（如果有的话）得以确定。来自不同海拔带的物种的潜在杂交是特别有趣的，以了解导致迁移到新栖息地的因素。此外，这些分析将为一些稀有物种的保护工作提供相关数据，并有助于理解在隔离条件下威胁许多生物的理论过程，通过杂交灭绝。

9902276Jansen and Goertzen Oceanic islands are ideal natural laboratories for studying evolutionary processes. Their isolation, environmental variability, and easily determined ages have aided biologists ever since Darwin in unraveling the forces behind evolutionary change. Our understanding of natural hybridization, a potentially major force in plant and animal evolution, has been advanced considerably by studies of species in the Hawaiian and Juan Fernandez islands in particular. Under the direction of Dr. Robert K. Jansen at the University of Texas at Austin, graduate student Leslie Goertzen is studying the role of hybridization in the evolution of the plant genus Argyranthemum (family Asteraceae). This group of 24 species found only in the Macaronesian archipelagos (Canaries, Madeira, and Salvage islands) is a spectacular example of adaptive radiation throughout the islands' elevational zones and has many characteristics which make it a model system for addressing evolutionary questions. This study will examine evidence for ancient introgression in the genus as well as the dynamics and consequences of contemporary species contact. A phylogenetic framework for these island plants will be constructed using variable nuclear DNA sequences, and a statistical comparison between these data and maternally inherited chloroplast DNA will be performed. Preliminary data suggest significant incongruence between the two data sets for several species pairs, raising the possibility of introgressive hybridization during the evolution of these lineages. Specific cases of contemporary hybridization will be examined by screeningnatural and hybrid populations for species-specific nuclear and chloroplast genetic markers. This will allow the direction and extent of interspecific gene flow, if any, to be determined. Potential hybrids of species from different elevational zones are of special interest, for understanding factors causing shifts into new habitats. In addition, the analyses will provide data of relevance to conservation efforts for several rare species and contribute to the understanding of a theoretical process which threatens many organisms in isolated conditions, extinction via hybridization.