Collaborative Research: Adaptive and nonadaptive mechanisms of phenotypic evolution in response to urbanization

世界上一半以上的人口生活在城市，而城市地区是地球上增长最快的生态系统之一。城市化导致了巨大的环境变化，从自然区到建筑和道路的转变，到空气、水、光和噪音污染的增加。城市化通常会减少生物多样性，但它也会影响生物进化的方式。在城市中茁壮成长的生物通常在形态、行为和生理上与农村地区相同物种的种群不同。这些差异是如何产生的？这个项目的焦点是在美国和国外的城市中最常见和最明显的动物之一：灰松鼠。灰松鼠为探索城市化影响进化的不同方式提供了一个理想的模型系统。灰松鼠有两种常见的毛色--灰色和黑色--这是由单个基因决定的。这种阴郁的形式过去在美国东北部的大部分地区很常见，但今天它主要在城市中盛行。为什么忧郁的松鼠在乡村森林里衰落了，但在城市里坚持了下来？该项目的结果将阐明城市化如何影响生物体进化方式的根本问题，即城市和周围农村地区的进化变化在多大程度上是由于自然选择、机会或两者的结合。该项目将吸引数以千计的公民科学家和学生记录对松鼠毛色的观察，并在他们的后院集体测量城市化如何塑造进化。这项研究将专门解决长期存在的关于城市进化和更广泛的进化生物学的问题，并帮助指导加强城市生物多样性和人类福祉的努力。研究将整合10个重复城市的人口统计学和基因组方法，以了解黑社会如何随着城市化而进化。首先，黑化病的空间差异将在每个城市进行表征，以测试黑化病是否从城市核心持续下降到乡村森林。其次，基因组学工具将被用来调查适应性自然选择与非适应性过程在多大程度上推动了黑化病从城市到农村地区的变化，包括随机引入和在城市环境中的传播。第三，将进行实验以了解自然选择的原因，测试城市化改变城市和农村森林中不同物种对不同死亡来源的脆弱性的想法。公民科学家将参与一项在线实验，以测量城市和农村环境中每一种变形的可见度，并比较每种环境中对这些变形的捕食率。这一奖项反映了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。

Over half of the world’s population lives in cities, and urban areas are among the fastest growing ecosystems on Earth. Urbanization causes dramatic environmental change, from the conversion of natural areas to buildings and roads, to increased air, water, light, and noise pollution. Urbanization often reduces biodiversity, but it can also affect the way organisms evolve. Organisms that thrive in cities commonly differ in their morphology, behavior, and physiology from populations of the same species in rural areas. How do these differences arise? This project’s focus is one of the most common and visible animals in cities in the United States and abroad: gray squirrels. Gray squirrels provide an ideal model system for exploring the different ways urbanization affects evolution. Gray squirrels have two common coat colors – gray and melanic – that are determined by a single gene. The melanic form used to be common in much of the northeastern United States, but today it is abundant primarily in cities. Why did melanic squirrels decline in rural forests but persist in cities? Results from this project will shed light on fundamental questions about how urbanization affects the way organisms evolve, that is, the degree to which evolutionary change in cities and surrounding rural areas is due to natural selection, chance, or a combination of both. The project will engage thousands of citizen scientists and students in recording observations of squirrel coat colors and collectively measuring in their backyards how evolution is shaped by urbanization. The research will address longstanding questions about urban evolution specifically and evolutionary biology more generally and help guide efforts to enhance biodiversity and human well-being in cities.The research will integrate demographic and genomic approaches across 10 replicate cities to understand how melanism evolved in response to urbanization. First, spatial variation in melanism will be characterized in each city to test whether melanism consistently declines from the urban core into rural forests. Second, genomic tools will be used to investigate the degree to which changes in melanism from urban to rural areas are driven by adaptive natural selection versus nonadaptive processes, including chance introductions and dispersal through the urban environment. Third, experiments will be conducted to understand the causes of natural selection, testing the idea that urbanization alters vulnerability of different morphs to different sources of mortality in cities and rural forests. Citizen scientists will be engaged in an online experiment to measure the visibility of each morph in urban and rural environments, and predation rates on the morphs will be compared in each environment.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.