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

人口规模呈指数级增长，反过来，城市环境是为数不多的快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的家园。加拉帕戈斯群岛目前每年接待22.5万名游客，拥有21300多名永久居民。因此，人类改变了自然栖息地，并将寄生虫引入加拉帕戈斯群岛，如寄生巢蝇（Philornis downsi），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，城市地区的小型地雀（Geospiza fuliginosa；达尔文雀的一种）更健康，受寄生虫的影响更小，这表明城市地区的鸟类能更好地抵御寄生虫。这项研究的目的是确定为什么城市地区的达尔文雀受寄生巢蝇的影响比非城市地区的雀要小。这项研究将首先探索城市雀类产生了哪些特定的免疫反应来降低它们的寄生虫负担。这项工作将确定这些增强的免疫反应是否由以下因素驱动：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2)城市人口免疫系统的遗传基因变化。总体而言，该研究旨在通过确定在新环境中对新寄生虫免疫的潜在环境或进化基础，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发与研究相关的K-12课堂活动、公开演讲和在线视频，从本地到国际范围的更广泛影响。这项研究将使用一系列的实地实验研究来确定达尔文雀在城市化过程中可能发生的免疫变化，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和表征候选免疫基因在不同地点的雀类中的基因表达来确定城市和非城市雀的免疫机制差异。其次，研究将通过实验确定城市和非城市雀类与人类食物的补充，从而确定雀类免疫力和寄生虫负担的差异，从而确定城市地区食物供应增加等环境因素是否驱动了雀类免疫力的差异。最后，采用普通园林实验的方法，将城市雀与非城市雀的幼鸟在原生境或新生境中交叉培养，确定城市雀对寄生虫的免疫是否具有适应性进化，并对其免疫和寄生虫负担进行量化。加拉帕戈斯群岛系统在解决城市生态进化的基本问题方面是强大的，因为它有大量已建立的基础，在实地进行实验的能力，以及该岛相对较新的城市化进程。该项目由环境生物学部的进化过程集群和综合生物系统学部的共生、防御和自我识别项目共同资助。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。

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.