Dissertation Research: Breeding Systems in Gaertnera (Rubiaceae): A Phylogenetic Approach to the Evolution of Dioecy from Distyly

小行星9701008 研究生Simon Malcombep在密苏里州植物园Peter Raven博士的指导下，正在研究旧大陆热带灌木Gaertnera（茜草科，Rubiaceae）的几个物种的授粉和花特征的进化。沿着与几个相关的属，这些植物被认为是祖先拥有两性花与两个不同的风格长度（说是二型），假设条件，以促进远系繁殖。在该属内，有几个物种已经变成雌雄异株的状态，在不同的植物上有不同的雄性（花粉）和雌性（胚珠或种子）花，这种状态强制执行远系繁殖。在试图确定是什么生态或遗传因素驱动了向雌雄异株进化的过程中，传粉者的有效性（花是昆虫授粉的）和遗传近交衰退的相对作用是不可能解开的。该项目的一个主要目标是将广泛的形态学研究与从所有物种产生的新DNA序列数据相结合，为48种左右的Gaertnera物种提供一个良好的支持。然后，基于实地的授粉和结实的研究可以有针对性的物种对或群体，对比雌雄异株和雌雄异株的条件共存。 在旧大陆热带地区的实地收集和传粉者和种子集的观测工作将提供必要的材料的形态和分子分析的Gaertnera灌木物种之间的系统发育关系，导致这些植物的分类和可靠的标记识别。此外，还将对不同物种对和群体中与传粉者有效性和种子结实有关的生态条件进行测试，以评估促进植物中异育性进化的因素。

9701008 Raven Graduate student Simon Malcombep, under the direction of Dr. Peter Raven at the Missouri Botanical Garden, is studying the several species of the Old World tropical shrub Gaertnera (madder family, Rubiaceae) for the evolution of pollination and floral features. Along with several related genera, these plants are considered ancestrally to possess hermaphroditic flowers with two different style lengths (said to be distylous), a condition hypothesized to promote outbreeding. Within the genus, several species have changed to the dioecious condition, with separate male (pollen) and female (ovule or seed) flowers on separate plants, a condition obligately enforcing outbreeding. The relative roles of pollinator effectiveness (the flowers are insect pollinated) and genetic inbreeding depression have been impossible to disentangle, in trying to determine what ecological or genetic factors drive the evolution toward dioecy. A well supported phylogeny for the 48 or so species of Gaertnera is one major goal of this project, to be reached by combining extensive morphological studies with new DNA sequence data generated from all the species. Then, field-based studies of pollination and seed set can be targeted to species pairs or groups where contrasting distylous and dioecious conditions coexist. Field collecting in the Old World tropics and observational work on pollinators and seed set will provide necessary materials for morphological and molecular analyses of the phylogenetic relationships among the species of Gaertnera shrubs, leading to improved classification of these plants and reliable markers for identification. In addition, tests will be made of ecological conditions pertaining to pollinator effectiveness and seed set in various species pairs and groups, to assess factors that promote the evolution of dioecy in plants.