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

9701008乌鸦研究生Simon Malcombep在密苏里州植物园的Peter Raven博士的指导下，正在研究东半球热带灌木Gairtnera(茜草科，茜草科)的几个物种的授粉和花特征的进化。与几个相关的属一起，这些植物的祖先被认为具有两种不同花柱长度的两性花(据说是茎)，这种情况被认为是为了促进近亲繁殖。在该属内，有几个物种已转变为雌雄异株状态，在不同的植物上有单独的雄花(花粉)和雌花(胚珠或种子)，这是一种强制进行异株繁殖的条件。传粉者效率(花是昆虫授粉的)和遗传近亲繁殖抑制的相对作用一直不可能分开，试图确定是什么生态或遗传因素推动了雌雄异株的进化。本项目的一个主要目标是通过将广泛的形态研究与从所有物种产生的新DNA序列数据相结合来实现该项目的一个主要目标，即建立一个得到充分支持的盖尔特纳属约48种的系统发育。然后，基于田间的授粉和结实研究可以针对存在相反的茎和雌雄异株条件的物种对或群体。东半球热带的野外采集和对传粉者和结实的观察工作将为分析加尔特纳灌木物种之间的系统发育关系提供必要的材料，从而改进这些植物的分类，并为鉴定提供可靠的标记。此外，还将对不同物种对和种群中传粉者的有效性和结实的生态条件进行测试，以评估促进植物雌雄异株进化的因素。

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.