DISSERTATION RESEARCH: Geographic Variation in Pollinators, Outcrossing, and the Incipient Evolution of Dioecy in Echinocereus coccineus (Cactaceae)

生物学中的一个基本问题是：为什么有不同的性别？分开的两性避免了最糟糕的近亲繁殖：自交受精。在动物传粉的植物中，假设在某些地区（如山顶、沙漠）进化出不同的性别，因为那里不太专门的传粉者主要是给这些植物自花授粉。另一种假设是两性分离的进化，因为性功能所需的资源（如水）是稀缺的，如果两性分离，可以更有效地分配。红杯仙人掌提供了一个独特的机会来同时测试这两种假设，因为它们同时拥有两性同体（两性在一起）和雌雄异株（两性分开）的种群。这个物种是由雌雄异株种群及其周围的不太专业的蜜蜂授粉的，这支持了近亲繁殖避免假说。然而，雌雄异株种群也倾向于发生在干旱地区。这支持了资源分配假说。对植物、种群和景观尺度的遗传分析将决定蜜蜂产生的自花受精率是否足以产生雌雄异株。利用结构方程模型分析了传粉媒介、降雨等环境因子对雌雄异株进化的直接和间接影响。这项研究的资金将首次在自然种群中对近亲繁殖避免假说进行检验。为这个项目开发仙人掌的第一个微卫星标记导致了三个机构之间的合作，并对少数民族本科生进行了现代遗传技术的培训。

One of the fundamental questions in biology is: Why have separate sexes? Having separate sexes avoids the worst type of inbreeding: self-fertilization. In animal-pollinated plants it is hypothesized that separate sexes evolve in certain areas (e.g., mountain-tops, deserts) because the less specialized pollinators there predominantly self-fertilize these plants. An alternative hypothesis is separate sexes evolve because resources (e.g., water) needed for sexual function are scarce, and can be allocated more efficiently if the sexes are separated. Claret-cup cacti present a unique opportunity to concurrently test these two hypotheses because they possess both hermaphroditic (sexes together) and dioecious (sexes separated) populations. This species is pollinated by less-specialized bees in and around dioecious populations, which supports the inbreeding-avoidance hypothesis. However, dioecious populations also tend to occur in arid areas. This supports the resource-allocation hypothesis. Genetic analyses at the plant, population and landscape scale will determine if the rate of self-fertilization produced by bees is sufficient to produce dioecy. The direct and indirect effects of pollinators, rainfall and other environmental factors on the evolution of dioecy will be assessed using Structural Equation Modeling. Funding of this research will provide the first test of the inbreeding-avoidance hypothesis in natural populations. Developing the first microsatellite markers for cacti for this project has led to collaborations across three institutions and training of minority undergraduates in modern genetic techniques.