The Bio- and Phylogeography of Sympatric Speciation in Rhagoletis

Rhagoletis同域物种形成的生物和系统发育地理学

• 批准号: 0445353
• 负责人: Jeffrey Feder
• 金额: $ 45.83万
• 依托单位: University of Notre Dame
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2005
• 资助国家: 美国
• 起止时间: 2005-03-01 至 2009-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0445353&HistoricalAwards=false
• 关键词: Bio; Phylogeography; Sympatric; Speciation; Rhagoletis

The intellectual and scientific focus of the research centers on how new species of Rhagoletis pomonella fruit flies form. Speciation occurs as genetic barriers to gene flow evolve between populations that cause them to become reproductively isolated from one another. Traditionally, speciation has been thought to require that populations be completely geographically isolated by physical barriers to movement (e.g., mountain ranges, large rivers, oceans). By precluding individuals from moving between populations, geographic isolation results in genetic changes occurring independently between populations which, over time, can accumulate to the point that the populations evolve into reproductively isolated species. The apple maggot fly, Rhagoletis pomonella, has been argued to be a possible exception, however. As early as 1864, Benjamin Walsh hypothesized that certain insects that specialize on attacking specific plants could speciate without geographic isolation ("in sympatry") in the process of them shifting and ecologically adapting to new host plants. In particular, Walsh cited the shift of Rhagoletis pomonella from its native host plant hawthorn (Crataegus) to introduced, domesticated apple trees in the United States - an event that occurred in the 1850's - as a real time example of his idea of sympatric speciation in action. Subsequent genetic studies have confirmed Walsh's hypothesis that the apple and hawthorn-infesting forms of Rhagoletis pomonella are partially reproductively isolated "host races", potentially in the first stages of diverging into new species. An important factor responsible for the divergence of the apple and hawthorn flies is that apple and hawthorn trees fruit at different times of the year, resulting in the one-generation per year life cycles of apple and hawthorn flies having to be offset in order for them to be able to attack apple vs. hawthorn trees. Recently, an interesting twist to the Rhagoletis story has been discovered. Some of the genes responsible for the difference in the life history of apple and hawthorn flies in the United States may have originated over a million years ago in an isolated population of hawthorn-infesting flies in Mexico. These genes were introduced into the U.S. in the distant past during a period when the Mexican and US hawthorn-fly populations came into contact (perhaps 500,000 years ago), and very recently these genes helped facilitate the shift to domesticated apple following the planting of apples in the US by European colonists. Thus, geographic isolation and gene flow may act in conjunction with ecological specialization to help trigger "sympatric" speciation events (i.e., the introduction of apples into the U.S. provided hawthorn flies with a new ecological niche - a temporal resource island - that they were able to take advantage of, in part, because of the genetic variation they possessed due to past gene flow from Mexico). The current grant proposal will test this biogeographic hypothesis thorough an extensive analysis of DNA sequences of genes located throughout the genome of Rhagoletis flies. The research will involve a survey of flies collected throughout Mexico to determine the extent of the geographic range of Rhagoletis flies in the country and pinpoint possible sources of gene flow into the U.S. in the past. In addition, the genetic analysis will indicated whether certain genes and genomic regions have characteristics that made them more or less prone to have moved into the US fly population (e.g., whether or not the genes reside within inversions - stretches of chromosomes that have different linear orders of genes along them - that have been hypothesized to retard gene flow between species). In this manner, the research will resolve the genetic history underlying the recent shift and formation of the new form of apple-infesting Rhagoletis pomonella. The broader impacts and societal benefits of the research are multifaceted. The project will integrate science training and educational activities at the local, community, University, and international levels. The study will involve the participation of a Post-Doctoral associate and graduate, undergraduate, and high school students in various aspects of the work ranging from field and laboratory research to class modules designed to give high school students and educators hands on experience with molecular genetic techniques and analysis. The funding provided by the current proposal will also expand and strengthen the Population Biology program at the University of Notre Dame at a critical stage of its development. In addition, the proposed research represents an international collaboration between researchers at Notre Dame and two distinguished Mexican colleagues, Dr. Martin Aluja and Dr. Juan Rull, at the Ecological Institute in Xalapa, Veracruz. Drs. Aluja and Rull have received parallel support from CONACyT to fund the collaboration. Finally, the proposed Rhagoletis research has significant applied, as well as basic, scientific implications. Rhagoletis pomonella is a major economic pest of apples, and related species attack cherries, blueberries, and several other crops. The question of the extent and host range of Rhagoletis pomonella in Mexico has important implications concerning the import and export of fruit between the two countries, as well as how new populations of pest species form and can be controlled. The impact of the proposed research is therefore ranges from new basic and applied scientific findings, to educational and societal benefits.

这些研究的智力和科学焦点集中在新物种如何形成波蒙氏树冠果蝇上。物种形成是由于种群之间基因流动的遗传障碍的进化，导致种群之间在生殖上相互隔离。传统上，物种形成被认为要求种群在地理上被物理上的流动障碍(如山脉、大河、海洋)完全隔绝。通过阻止个体在种群之间流动，地理隔离导致种群之间独立发生的基因变化，随着时间的推移，这些变化可以累积到种群进化为繁殖隔离物种的程度。然而，苹果蝇(Rhagoltis Pomonella)可能是一个例外。早在1864年，本杰明·沃尔什就假设，某些专门攻击特定植物的昆虫在它们转移和生态适应新寄主植物的过程中，可以在不受地理隔离的情况下形成物种。特别是，沃尔什引用了波蒙氏树冠从原生寄主山楂(Crataegus)到美国引进驯化苹果树的转变-这一事件发生在19世纪50年代的S-作为他的共地物种形成思想在行动中的实时例子。随后的遗传学研究证实了沃尔什的假说，即苹果和山楂肆虐的波蒙氏树根霉是部分繁殖隔离的“寄主小种”，可能处于分化成新物种的第一阶段。苹果和山楂果蝇分化的一个重要原因是苹果树和山棘果树在一年中不同的时间结果，导致苹果和山棘果蝇一年一代的生活周期必须被抵消，以便它们能够攻击苹果和山楂树。最近，拉戈尔蒂斯的故事出现了一个有趣的转折。造成美国苹果和山棘果蝇生活史差异的一些基因，可能起源于100多万年前墨西哥一个孤立的山楂果蝇种群。这些基因是在遥远的过去墨西哥和美国山棘蝇种群接触的时期(大约在50万年前)引入美国的，最近这些基因帮助促进了欧洲殖民者在美国种植苹果后向驯化苹果的转变。因此，地理隔离和基因流动可能与生态专门化一起作用，以帮助触发“同域”物种形成事件(即，苹果被引入美国为山楂果蝇提供了一个新的生态位--一个暂时的资源岛--它们能够利用的部分原因是，由于过去来自墨西哥的基因流动，它们拥有遗传变异)。目前的拨款方案将通过对树头蝇基因组中所有基因的DNA序列的广泛分析来检验这一生物地理学假说。这项研究将涉及对墨西哥各地收集的苍蝇进行调查，以确定该国树头蝇的地理范围，并查明过去流入美国的可能基因来源。此外，遗传分析将指出某些基因和基因组区域是否具有使它们或多或少容易进入美国苍蝇种群的特征(例如，这些基因是否位于倒位内--一段具有不同线性顺序的基因的染色体--被假设为延缓了物种之间的基因流动)。通过这种方式，这项研究将解决最近苹果侵染的庞氏树冠杆菌新形式转变和形成背后的遗传史。这项研究的广泛影响和社会效益是多方面的。该项目将整合地方、社区、大学和国际各级的科学培训和教育活动。这项研究将包括一名博士后助理以及研究生、本科生和高中生参与这项工作的各个方面，从现场和实验室研究到课程模块，这些模块旨在为高中生和教育工作者提供分子基因技术和分析的实践经验。目前提案提供的资金还将扩大和加强圣母大学的人口生物学课程，该课程正处于发展的关键阶段。此外，这项拟议的研究代表着圣母大学的研究人员与韦拉克鲁斯哈拉帕生态研究所的两位杰出的墨西哥同事马丁·阿卢贾博士和胡安·鲁尔博士之间的国际合作。Aluja博士和Rull博士得到了CONACyT的平行支持，为合作提供资金。最后，拟议中的Rhagoltis研究具有重大的应用和基本的科学意义。苹果纹枯病是苹果的一种主要经济害虫，其近缘种危害樱桃、蓝莓和其他几种作物。波蒙氏菌在墨西哥的范围和寄主范围的问题对两国之间的水果进出口以及如何形成和控制新的害虫种群具有重要的意义。因此，拟议研究的影响范围从新的基础性和应用性科学发现到教育和社会效益。