BEE: Testing eco-evolutionary effects of genetic drift and gene flow in stressful environments

栖息地的丧失正在将世界上的动植物分裂成更小、更孤立的碎片。与此同时，许多生物还必须承受环境的快速和压力变化。这些因素加在一起，可能会增加物种灭绝的风险。一种可能的逃脱灭绝的方法是通过适应。然而，遗传多样性较低的小种群可能无法及时适应环境变化的步伐。有时用来增加遗传多样性的一种方法是将个体从一个地点转移到另一个地点。从理论上讲，这种方法可以通过增加适应的潜力和速度来防止物种灭绝。但是，目前还不清楚这种情况是如何发生的，或者它多久起作用一次。该项目将确定，与没有接受新基因的种群相比，接受新基因的小种群是否能够更快地适应紧张的环境并避免灭绝。该项目将重点研究户外水箱中的东方蚊子。这些鱼缸将具有不同数量和类型的遗传多样性，其中一些将被加热以使其环境紧张。研究人员将在几年内测量基因和每个鱼缸中鱼的数量的变化。在实验结束时，他们将确定加热水箱中的鱼是否比非加热水箱中的鱼具有更好的抗热能力。与高温适应有关的基因将被识别出来，研究人员将评估接收新鱼的水箱是否不太可能灭绝。这个项目将揭示导致适应和灭绝的遗传因素。重要的是，这项工作的结果将为管理决策提供信息，并改善生物多样性保护。更广泛的影响包括通过教师培训和学生夏令营活动扩大K-12教育。作为该项目的一部分，一名博士后研究员和几名研究生和本科生将接受培训。快速适应有可能拯救面临新的、有压力的环境的人群。然而，只有当种群能够在压力条件下生存，并且有足够的基因变异对选择做出反应时，这种情况才会发生。大多数进化挽救文献集中在局部站立变异或从头突变的作用上，很大程度上忽视了基因流和遗传漂移的有利或制约作用。最近的证据表明，基因流动可能是导致种群增长的重要变异来源，特别是在受体种群较小且近亲交配的情况下。然而，自然种群缺乏基因流动可以防止灭绝的直接证据，基因流动的长期好处，如增加适应潜力，几乎从未显示出来。这项拟议的研究将调查近期进化史上的差异(即遗传漂移和基因流)如何影响面对新压力时的适应性反应和持久性。该项目将产生具有不同近期进化史的东部蚊虫实验种群。研究人员将使用急性应激实验来测试进化史对初始和进化的热耐性的影响。一个多代中观实验将被用来测试与良性环境相比，进化史如何影响暴露在慢性新压力(接近致命的高温)下的种群的个体适应性、种群动态和灭绝概率。最后，研究人员将从野生种群和从中游种群收集的时间序列生成全基因组序列数据，以确定潜在的适应和人口统计学的基因组机制。该项目将为基因漂移和基因流动的生态进化作用提供一个独特的机械观点，并可能从根本上改变人们对基因流动在当代人口中的作用的普遍接受的预期。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Habitat loss is splitting the world’s plants and animals into smaller and more isolated fragments. At the same time, many organisms also have to withstand rapid and stressful changes to their environment. Combined, these factors can increase extinction risk. One possible escape from extinction is through adaptation. Yet, small populations with low genetic diversity may be unable to adapt in time to keep pace with environmental change. An approach sometimes used to increase genetic diversity is to move individuals from one site to another. In theory, this method could prevent extinction by increasing the potential and speed of adaptation. But, it is unknown how this occurs, or how often it works. This project will determine whether small populations that received new genes can adapt faster to a stressful environment and avoid extinction compared to those that have not. This project will focus on studying eastern mosquitofish in outdoor tanks. These fish tanks will have different amounts and types of genetic diversity, and some will be heated to make their environment stressful. The researchers will measure changes in genes and in the number of fish in each tank over several years. At the end of the experiment they will determine whether fish from heated tanks can resist heat better than fish from unheated tanks. Genes involved in adaptation to heat will be identified, and the researchers will assess whether tanks that received new fish were less likely to go extinct. This project will reveal the genetic factors that contribute to adaptation versus extinction. Importantly, outcomes from this work will inform management decisions and improve biodiversity conservation. Broader Impacts include K-12 outreach through teacher training and summer camp activities for students. A postdoctoral researcher and several graduate and undergraduate students will be trained as part of this project. Rapid adaptation has the potential to rescue populations facing novel, stressful environments. Yet, this will only happen if populations can survive under stressful conditions and also have sufficient genetic variation to respond to selection. Most of the evolutionary rescue literature focuses on the roles of local standing variation or de novo mutation, largely ignoring the beneficial or constraining roles of gene flow and genetic drift. Recent evidence suggests that gene flow may be an important source of variation that can result in increased population growth, especially when recipient populations are small and inbred. However, direct evidence that gene flow can prevent extinction is lacking from natural populations, and long-term benefits of gene flow such as increased adaptive potential have almost never been shown. The proposed research will investigate how differences in recent evolutionary history (i.e., genetic drift and gene flow) affect adaptive response and persistence in the face of novel stress. The project will generate experimental populations of eastern mosquitofish with different recent evolutionary histories. The researchers will use acute stress experiments to test the effects of evolutionary history on initial and evolved thermal tolerance. A multigenerational mesocosm experiment will be used to test how evolutionary history affects individual fitness, population dynamics, and extinction probability in populations exposed to chronic novel stress (near-lethal heat) compared to a benign environment. Finally, the researchers will generate whole genome sequence data from wild populations and from a time series collected from the mesocosm populations to identify genomic mechanisms underlying adaptation and demography. This project will provide a unique mechanistic view of the eco-evolutionary roles of genetic drift and gene flow and may fundamentally change generally accepted expectations about the role of gene flow in contemporary populations.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.