DISSERTATION RESEARCH: Genetic Basis and Adaptive Significance of Key Developmental Traits Underlying Ecological Differences Between Sympatric Sister Species

大多数物种是在地理屏障将种群长期隔开的情况下形成的。为了使物种保持独特，一旦它们彼此接触，它们必须进化出生殖隔离，通常是通过生态分化。如果没有生殖隔离，刚开始的物种将杂交并融合回单一物种。如果没有生态分化，激烈的竞争往往会导致一个物种局部灭绝。目前共存的物种可能在物理上分开时进化出了生态差异，或者它们可能通过选择在同一地区进化出差异，以最大限度地减少杂交或竞争。人们对允许物种在同一地区共存的生态特征差异或导致物种之间生态差异的遗传位点知之甚少。这项研究将确定导致北美西部两个野生花卉物种共存的生态差异的特征和遗传位点。分布广泛的点滴虫及其相对稀有的姊妹种裸露水母在一些地区共存，但生活在不同的微生境中，这些微生境在夏季干旱开始时有所不同。裸腹水母生长在初春干燥的蛇形山坡上，而水母则栖息在短暂的溪流中，那里的干旱造成的死亡晚于裸露水母的栖息地。这种罕见的特有植物具有几个可能适应较早干旱的特征，包括诱导开花的临界光周期较短，导致较早产生开花枝(抽苔期)，以及比更常见的点滴草更早的开花时间。了解稀有特有物种是如何与更广泛的物种一起维持的，对于保护和保护生物多样性具有重要意义。确定实现物种共存的潜在遗传变化将有助于阐明有助于维持物种多样性的遗传、生态和进化过程之间的相互作用。该项目将保持和发展新的指导机会，针对初中、高中和本科生水平上代表不足的群体。拟议的研究结果将通过演讲和出版物向公众和科学界广泛传播。该项目将明确测试维持两个密切相关物种的空间、表型和遗传差异的生态和进化力量。共生物种之间的生态相似性可能导致竞争排斥。因此，生态分化是稳定共存的必要前提。常见的点滴草和稀有的地方性裸露点滴草之间的开花时间差异被假设为允许这些物种通过栖息在不同的微生境中而共处，而不同的微生境在夏季干旱开始时不同。三个数量性状基因座(QTL)已经被发现，它们深刻地影响着临界光周期和抽苔期的差异，并且已经进行了遗传定位，但我们不知道这些基因座在自然界中如何影响小生境分化和物种相互作用。本项目将利用QTL定位、相互移植和竞争实验来检验：(1)田间开花时间差异与实验室光周期和抽苔是否具有相同或不同的遗传基础；(2)光周期和抽苔基因座是否具有适应性，并通过促进生态位分化而实现共存；(3)生态或生殖性状移位是否导致这两个密切相关的共生物种的开花时间差异。

Most species are formed when geographic barriers physically separate populations for long periods of time. For species to remain distinct once they are in contact with one another they must evolve reproductive isolation often through ecological differentiation. Without reproductive isolation incipient species will hybridize and fuse back together into a single species. Without ecological differentiation intense competition will often cause one species to go locally extinct. Species that presently co-occur may have evolved ecological differences while physically separated, or they may have evolved differences in the same area through selection to minimize hybridization or competition. Little is known about the ecological trait differences that allow species to coexist in the same area or the genetic loci responsible for ecological differences between species. This study will identify the traits and genetic loci underlying ecological differences that enable coexistence between two western North American wildflower species. The broadly distributed Mimulus guttatus, and its relatively rare sister species Mimulus nudatus co-occur in some areas but live in distinct microhabitats that differ in the onset of summer drought. Mimulus nudatus grows on serpentine slopes that dry out early in the spring, while M. guttatus inhabits ephemeral streams where drought imposed death is later than in the M. nudatus habitat. The rare endemic possesses several traits that are likely adaptations to earlier drought, including a shorter critical photoperiod to induce flowering resulting in an earlier production of a flowering shoot (bolting) and an earlier flowering time than the more common M. guttatus. Understanding how rare endemic species are maintained with more widespread species has important implications for conservation and the preservation of biodiversity. Determining the underlying genetic changes to enable species coexistence will shed light on the interaction among genetic, ecological, and evolutionary processes that contribute to the maintenance of species biodiversity. This project will maintain and develop new mentoring opportunities targeting underrepresented groups at the middle school, high school, and undergraduate level. The results of the proposed research will be broadly disseminated though talks and publications to the public and scientific community.This project will explicitly test the ecological and evolutionary forces maintaining spatial, phenotypic and genetic differences between two closely related species of Mimulus. Ecological similarity between sympatric species may lead to competitive exclusion. Consequently, ecological divergence is a necessary prerequisite for stable coexistence. Differences in flowering time between the common M. guttatus and the rare endemic M. nudatus are hypothesized to allow these species to occur in sympatry by inhabiting distinct microhabitats that differ in the onset of summer drought. Three quantitative trait loci (QTL) have been identified that profoundly influence differences in critical photoperiod and bolting and have already been genetically mapped, yet we do not know how these loci contribute to microhabitat differentiation and species interactions in nature. This project will utilize QTL mapping, reciprocal transplant and competition experiments to test: (1) whether flowering time differences in the field have the same or different genetic basis from photoperiod and bolting in the lab, (2) whether photoperiod and bolting loci are adaptive and enable coexistence by contributing to niche differentiation, and (3) whether ecological or reproductive character displacement are responsible for flowering time differences in the two closely related sympatric species.