Experimental speciation: reinforcement in Drosophila melanogaster

当种群进化出繁殖障碍时，物种形成就发生了。理解这些障碍是如何形成的是进化生物学中一项长期的挑战。这是因为预计反复的移徙会消除人口之间出现的任何差异。完成物种形成的一种方式是通过一个叫做强化的过程。当杂交后代不太适合时，自然选择倾向于避免杂交，强化就会发生。这个项目使用实验进化——研究进化过程中的变化——来追踪种群间长期的繁殖障碍。这项工作将研究种群之间相对较弱的繁殖障碍是随着时间的推移而加强还是减弱。利用这些数据，研究人员将确定可能发生强化的情况。作为该项目的一部分，高中生、本科生和研究生将接受科学教育和培训。在当地一所中学和童子军开展的一项拓展计划将增加对遗传学的了解，并促进弱势群体对科学的兴趣。支持和反对强化生殖隔离进化的证据主要来自自然种群的比较方法和快照研究。然而，当试图将生殖隔离模式归因于特定的进化力量时，这些方法往往遇到困难。这个项目将直接检验强化选择可以压倒基因流的均质化力量的假设。为了验证这一假设，这项工作将跟踪显示出某种程度的初始生殖隔离的黑腹果蝇种群的生殖隔离的进化。一些实验种群将保持异域生存，而另一些将经历基因流动。在这些种群中，对杂交的选择强度将被操纵。对这些种群进行竞争性和非竞争性生殖隔离的一系列措施将揭示三个问题的答案。首先，强化能够加强生殖隔离的频率和持续程度如何？第二，对抗杂交的选择要有多强才会发生这种情况？第三，交配前（性）或交配后-合子前（配子）隔离在进化上更不稳定？该项目由进化过程和促进竞争研究的既定计划（EPSCoR）共同资助。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Speciation occurs when populations evolve barriers to reproduction. Understanding how these barriers form is a longstanding challenge in evolutionary biology. This is because recurrent migration is expected to erase any emerging differences between populations. One way to complete speciation is through a process called reinforcement. Reinforcement occurs where natural selection favors the avoidance of hybridization when hybrid offsprings are less fit. This project uses experimental evolution—studying evolutionary change as it occurs—to track reproductive barriers between populations over time. The work will examine whether relatively weak barriers to reproduction between populations are strengthened or decay over time. Using these data, the researchers will determine the scenarios under which reinforcement can occur. As part of this project, high school, undergraduate, and graduate-level students will receive science education and training. An outreach program operating at a local middle school and scout troop will increase exposure to genetics and promote interest in science amongst underrepresented groups. Evidence for and against the evolution of reproductive isolation by reinforcement comes largely from comparative approaches and snapshot studies in natural populations. However, these methods often encounter difficulties when trying to ascribe patterns of reproductive isolation to specific evolutionary forces. This project will directly test the hypothesis that reinforcing selection can overwhelm the homogenizing force of gene flow. To test this hypothesis, the work will follow the evolution of reproductive isolation in populations of Drosophila melanogaster that show some degree of initial reproductive isolation. Some experimental populations will remain allopatric, while others will experience gene flow. In these populations, the strength of selection against hybridization will be manipulated. A time series of measures of both competitive and non-competitive reproductive isolation from these populations will reveal the answers to three questions. First, how often and how consistently is reinforcement able to strengthen reproductive isolation? Second, how strong must selection against hybrids be for this to occur? Third, is pre-mating (sexual) or postmating-prezygotic (gametic) isolation more evolutionarily labile?This project is jointly funded by Evolutionary Processes and the Established Program to Stimulate Competitive Research (EPSCoR).This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.