SG: Eco-evolution in a concrete jungle: how rapid urbanization affects host-parasite interactions in the Galapagos Islands

人类人口规模正在呈指数级增长，而城市环境又是少数几个迅速扩张的生态系统之一。最近一个城市化的例子是加拉帕戈斯群岛，那里是标志性的达尔文雀类的家园。加拉帕戈斯群岛目前每年接待游客22.5万人，永久居民超过2.13万人。因此，人类改变了自然栖息地，并在加拉帕戈斯群岛引入了寄生虫，例如一种寄生的巢蝇(Philorris Down Si)，它会导致幼雀大量死亡。然而，最近的研究表明，与非城市地区的雀类相比，城市地区的小地雀(Geospiza fuliginosa；达尔文雀类的一种)更健康，受寄生虫的影响更小，这表明城市地区的鸟类对寄生虫的防御能力更强。这项研究的目的是确定为什么达尔文生活在城市地区的雀类比非城市地区的雀类受寄生巢蝇的影响更小。这项研究将首先探索城市雀产生哪些特定的免疫反应来降低它们的寄生虫负担。然后，这项工作将确定这些增强的免疫反应是由以下因素驱动的：1)环境，例如通过城市食物补充，可以增加分配给免疫的能量，或者2)城市人口中免疫系统的可遗传基因变化。总体而言，这项研究试图通过确定在新环境中对一种新寄生虫免疫的潜在环境或进化基础，来了解鸟类与寄生虫在城市化过程中的相互作用。拟议的工作还将包括通过开展与该研究相关的课堂K-12活动、公开演示和在线视频，从当地到国际范围内的更广泛影响。研究将使用一系列实验场研究来确定达尔文雀类因城市化而可能发生的免疫学变化，以及这些变化是由环境条件还是适应性进化驱动的。首先，这项工作将通过实验操纵寄生虫，并表征不同地点的候补免疫基因的基因表达，来确定城市和非城市雀类之间的免疫机制的不同。其次，这项研究将通过在城市和非城市地区用以人为基础的食物来试验性地补充雀类，然后确定雀类免疫和寄生虫负担，从而确定城市地区环境因素，如食物可获得性的增加，是否正在推动雀类免疫的差异。最后，这项研究将通过一个普通的花园实验来确定城市雀类是否已经适应性地进化出对这种寄生虫的免疫力，通过这种实验，城市和非城市雀类的幼鸟将在他们原来的或新的区域交叉培育，然后他们的免疫力和寄生虫负担将被量化。加拉帕戈斯系统在解决城市生态进化中的基本问题方面是强大的，因为它已经建立了大量的基础工作，能够在实地进行实验，而且岛屿的城市化相对较新。该项目由环境生物学部门的进化过程集群和综合组织系统部门的共生、防御和自我识别计划共同资助。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。

Human population size is increasing exponentially and, in turn, the urban environment is one of the few ecosystems that is rapidly expanding. A recent example of urbanization is in the Galapagos Islands, which is home to the iconic Darwin’s finches. The Galapagos currently hosts 225,000 tourists each year and is home to over 21,300 permanent residents. Consequently, humans have altered the natural habitat and introduced parasites to the Galapagos, such as a parasitic nest fly (Philornis downsi), which causes significant mortality to baby finches. However, recent work shows that small ground finches (Geospiza fuliginosa; a species of Darwin’s finch) in urban areas are healthier and less affected by the parasite compared to finches in non-urban areas, which suggests that birds are better defended against the parasite in urban areas. The goal of the research is to determine why Darwin’s finches in urban areas are less affected by the parasitic nest fly than finches in non-urban areas. The research will first explore what specific immune responses are being produced by the urban finches to lower their parasite burden. The work will then determine whether these heightened immune responses are driven by: 1) the environment, such as through urban food supplementation that could increase allocated energy to immunity, or 2) heritable genetic changes to the immune system within the urban population. Overall, the research seeks to understand bird-parasite interactions in response to urbanization by identifying the potential environmental or evolutionary basis of immunity to a novel parasite in a novel environment. The proposed work will also include broader impacts from a local to international scale through the development of in-class K-12 activities, public presentations, and online videos related to the research.The research will use a series of experimental field studies to determine the immunological changes potentially occurring in Darwin’s finches in response to urbanization and whether these changes are driven by environmental conditions or adaptive evolution. First, the work will determine what mechanisms of immunity differ between urban and non-urban finches by experimentally manipulating the parasite and characterizing gene expression of candidate immune genes in the finches across locations. Second, the research will determine whether environmental factors, such as increased food availability, in the urban area are driving differences in finch immunity by experimentally supplementing urban and non-urban finches with human-based food, then determining finch immunity and parasite burden. Lastly, the research will determine whether urban finches have adaptively evolved immunity to the parasite using a common garden experiment, whereby urban and non-urban finch young will be cross fostered in their original or new area, then their immunity and parasite burden will be quantified. The Galapagos system is powerful to address fundamental questions in urban eco-evolution because of the significant amount of established groundwork, the ability to perform experiments in the field, and the relatively recent urbanization of the islands.This project is co-funded by the Evolutionary Processes cluster in the Division of Environmental Biology and the Symbiosis, Defense and Self-recognition Program in the Division of Integrative Organismal Systems.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.