DISSERTATION RESEARCH: Genetic basis of population level divergence in flower morph production induced by variable threshold environmental conditions

与许多动物不同，植物是固着的，无法逃离不利的环境，因此它们必须依靠发育的灵活性来科普环境中不可预测的变化。 众所周知，植物通过响应诸如温度和日照长度的季节性线索来实现这一目标，并使用这些线索来启动主要的生活史转变，例如在一年中的适当时间从营养生长到开花。最引人注目的形态转换之一是同一植物上不同花型之间的转换。这类物种可以从一朵相对较大的花，吸引传粉者，促进个体植物之间的交配，变成一朵相对较小的花，部分原因是它不需要吸引动物来繁殖，因为它能够与自己交配。这种发展转变被认为是当环境线索达到阈值时触发的。然而，每种花的繁殖都有不同的结果;小的自花授粉花产生的近交后代与个体之间交配产生的后代相比，往往会受到活力降低的影响。研究人员将发现这些途径的遗传成分，这些遗传成分导致种群表现出不同的阈值，用于使用Mimulus douglasii（一种能够进行花形态转换的新兴模式植物）进行可变环境反应。他们将研究在自然田间条件下负责花形态转变的基因座的选择优势。一个预测是，生活在水和营养有限的恶劣环境中的种群将被选择降低阈值，并产生更多的自花授粉花朵，以节省资源，尽管近亲繁殖后可能会降低活力。这项研究的结果可用于增强对农业物种如何感知和响应环境的理解，并可用于修改作物，使其能够在新的环境下生长。植物适应新栖息地的方式将与达勒姆地区的小学、初中和高中学生分享。此外，研究人员将在实验室和现场指导杜克大学的本科生。 本研究将（1）通过检查阈值反应差异的分子遗传基础来确定多型环境反应阈值偏移如何发生，（2）评估这些遗传位点在自然田间条件下的适应性后果，以了解阈值偏移发生的原因。为了实现这些目标，两个种群的M。在极端环境反应下出现的douglasii将杂交形成F2个体。首先，将进行遗传作图实验，以找到与长日照光周期下产生特定花形态的阈值变化相关的基因组位点。从这一目标定位的基因座将形成第二行调查的基础：F3杂交个体将在两个领域共同的花园。相关的健身，将被测量包括发芽，花数，花的类型，和总种子产量每株植物。这些适合度测量将与为花形态产生阈值绘制的基因组位点相关。为了获得更深入的了解，研究人员获得了M. douglasii及其姊妹种M. kellogelae和一个近亲M. guttatus，其中后两个物种只表现出一种花形态。总的来说，这些数据将有助于理解影响生活史策略进化的阈值反应作用的遗传基础。

Unlike many animals, plants are sessile and unable to escape from unfavorable environments, so they must rely on developmental flexibility to cope with unpredictable changes in their environment. It is well known that plants accomplish this goal by responding to seasonal cues such as temperature and day length, and use these cues to initiate major life history transitions such as, from vegetative growth to flowering at the appropriate time of year. One of the most striking morphological switches is the shift between different flower forms on the same plant. Such species can shift from a flower that is relatively large and attracts pollinators that promotes mating between individual plants to a flower that is relatively much smaller, in part because it does not need to attract an animal to visit it to reproduce, because it is capable of mating with itself. This developmental shift is thought to be triggered when an environmental cue reaches a threshold. However, reproduction by each flower type comes with different consequences; small self-pollinating flowers produce inbred offspring that often suffer from a reduction in vigor compared to progeny produced from matings between individuals. The researchers will uncover genetic components of the pathways that result in populations exhibiting different thresholds for variable environmental responses using Mimulus douglasii, an emerging model plant that is capable of floral morph switching. They will examine the selective advantage of the loci responsible for floral morph shifts under natural field conditions. One prediction is that populations living in harsh environments with limited water and nutrients will be selected to lower their threshold and produce more self-pollinating flowers to save resources despite the potential reduction in vigor following inbreeding. The results of the proposed study could be used to enhance understanding of how agricultural species sense and respond to the environment, and could be used to modify crops to allow them to grow under novel environments. The ways in which plants can adjust to novel habitats will be shared with elementary, middle school, and high school students in the Durham area. Additionally the researchers will mentor Duke undergraduate students in the lab and the field. This study will (1) determine how a polyphenic environmental response threshold shift can occur, by examining the molecular genetic basis of the difference in threshold responsiveness and (2) assess the fitness consequences of these genetic loci under natural field conditions to understand why the shift in threshold occurred. To accomplish these goals two populations of M. douglasii that occur at the extremes of environmental responsiveness will be hybridized to form F2 individuals. First, a genetic mapping experiment will be done to find the genomic loci that correlate with a change in threshold for the production of particular floral morphs under long-day photoperiods. Mapped loci from this objective will form the basis for the second line of investigation: F3 hybrid individuals will be grown in two field common gardens. Correlates to fitness that will be measured include germination, flower number, flower type, and total seed production per plant. These fitness measurements will be correlated with the genomic loci mapped for floral morph production thresholds. To gain greater insights the researchers have the whole genome sequence data for M. douglasii, its sister species M. kelloggii, and an assembled and roughly annotated genome of a close relative, M. guttatus, where the latter two species exhibit only one flower morph. Collectively these data will aid in the understanding of the genetic basis of the role of threshold responses influencing the evolution of life history strategies.