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应对环境中不可预测的变化。众所周知，植物通过对季节信号(如温度和日长)的反应来实现这一目标，并利用这些信号来启动重大的生活史转变，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。这类物种可以从相对较大、吸引授粉者促进植物间交配的花朵转变为相对较小的花朵，部分原因是它不需要吸引动物造访它来繁殖，因为它能够与自己交配。这种发育变化被认为是当环境线索达到阈值时触发的。然而，每种花类型的繁殖都会带来不同的后果；小的自花授粉产生的近亲繁殖的后代，与个体之间交配产生的后代相比，往往活力下降。研究人员将使用Dimulus doutarsii揭示导致种群对不同环境反应表现出不同阈值的途径的遗传成分，Mimulus doutarsii是一种能够进行花形态转换的新兴模式植物。他们将研究在自然条件下负责花形态变化的基因座的选择优势。一种预测是，生活在水分和营养有限的恶劣环境中的种群将被选择降低门槛，生产更多的自花授粉，以节省资源，尽管近亲繁殖后活力可能会降低。拟议的研究结果可以用来加强对农业物种如何感知和响应环境的理解，并可以用来修改作物，使它们能够在新的环境下生长。达勒姆地区的小学生、初中生和高中生将分享植物适应新生境的方式。此外，研究人员还将在实验室和现场指导杜克大学的本科生。这项研究将(1)通过检查阈值响应差异的分子遗传学基础来确定多酚环境响应阈值漂移的发生方式，以及(2)评估这些遗传基因座在自然条件下的适合性结果，以了解阈值漂移发生的原因。为了实现这些目标，出现在环境反应极端的两个种群将杂交形成F2个体。首先，将进行一项遗传图谱实验，以找出与长日光周期下特定花形态产生阈值变化相关的基因组位置。根据这一目标绘制的基因座将构成第二线调查的基础：F3杂交个体将在两个田间普通花园中种植。要测量的适合度的相关因素包括发芽、花数、花型和每株种子总产量。这些适合度测量将与绘制的花形态生产阈值的基因组座位相关联。为了获得更深入的了解，研究人员拥有道格尔西支原体及其姊妹种凯洛吉支原体的全部基因组序列数据，以及近亲古特特斯支原体的组装和粗略注释的基因组，后两个物种只表现出一种花的形态。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.