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

密苏里植物园的研究生Simon Malcombep在Peter Raven博士的指导下，正在研究旧大陆热带灌木Gaertnera（菊科，Rubiaceae）的几种传粉和花特征的进化。与几个相关属一起，这些植物被认为祖先具有两种不同花柱长度的雌雄同体花（据说是二花），这种情况被假设为促进近亲繁殖。在本属中，一些物种已经转变为雌雄异株的状态，在不同的植物上有单独的雄花（花粉）和雌花（胚珠或种子），这种情况强制了近亲繁殖。在试图确定是什么生态或遗传因素推动雌雄异株进化的过程中，传粉者的有效性（花是昆虫授粉的）和遗传近交抑制的相对作用是不可能解开的。该项目的一个主要目标是，通过将广泛的形态学研究与所有物种产生的新的DNA序列数据相结合，为大约48个Gaertnera物种提供一个得到充分支持的系统发育。然后，基于实地的授粉和结实率研究可以针对不同的双花和雌雄异株共存的物种对或群体。在旧大陆热带地区的野外采集和传粉媒介和结实率的观测工作，将为狐苔属灌木种间系统发育关系的形态学和分子分析提供必要的资料，从而改进其分类和可靠的鉴定标记。此外，还将测试与传粉者有效性和不同物种对和群体的种子结实率有关的生态条件，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.