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

大多数物种都是在地理屏障将种群长时间隔离时形成的。为了使物种在彼此接触后保持独特性，它们必须经常通过生态分化来进化生殖隔离。如果没有生殖隔离，早期的物种将杂交并融合在一起成为一个单一的物种。如果没有生态分化，激烈的竞争往往会导致一个物种在当地灭绝。目前共存的物种可能在物理上分离时进化出生态差异，或者它们可能通过选择在同一地区进化出差异，以尽量减少杂交或竞争。人们对使物种在同一地区共存的生态性状差异或导致物种间生态差异的遗传位点知之甚少。这项研究将确定的特征和遗传位点的生态差异，使两个北美西部野花物种之间的共存。广泛分布的Mimulus guttatus及其相对罕见的姊妹种Mimulus nudatus在某些地区共存，但生活在不同的微生境中，这些微生境在夏季干旱的开始时有所不同。 Mimulusnudatus生长在蜿蜒的斜坡上，这些斜坡在早春干燥，而M。guttatus栖息在短暂的溪流，干旱造成的死亡比M。裸水母栖息地罕见的地方性有几个特点，可能是适应早期干旱，包括较短的临界光周期，以诱导开花，导致较早的生产开花枝条（抽薹）和较早的开花时间比更常见的M。点滴了解稀有特有物种如何与分布更广的物种共存，对养护和维护生物多样性具有重要意义。确定潜在的遗传变化，使物种共存将揭示遗传，生态和进化过程之间的相互作用，有助于维持物种的生物多样性。该项目将保持和发展针对初中、高中和本科阶段代表性不足群体的新的辅导机会。拟议的研究结果将通过讲座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的Mimulus物种之间空间，表型和遗传差异的生态和进化力量。同域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。在开花时间的差异之间的常见M。guttatus和罕见的特有M.据推测，裸石使这些物种能够同域生存，因为它们栖息在不同的微生境中，而这些微生境在夏季干旱开始时是不同的。三个数量性状基因座（QTL）已被确定，深刻影响的关键光周期和抽薹的差异，并已被遗传作图，但我们不知道这些基因座如何有助于微生境分化和物种的相互作用在自然界中。本项目将利用QTL作图、互作移植和竞争实验来检验：（1）田间开花时间的差异是否与实验室中的光周期和抽薹具有相同或不同的遗传基础，（2）光周期和抽薹位点是否是适应性的，是否通过促进生态位分化而能够共存，以及（3）生态或生殖性状的置换是否是导致两个密切相关的同域种开花时间差异的原因。

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.