Collaborative Research: Symbiosis as a fulcrum in a rapidly warming world

气候变化正在给地球居民带来前所未有的挑战。了解温度升高如何影响生物多样性和分布至关重要。然而，预测生物体对气候变化的反应是困难的，因为物种间的相互作用受到的影响不同于单个物种。此外，这些预测更加复杂，因为物种之间的相互作用通常涉及被称为共生体的“隐藏”微生物，它们似乎特别容易受到气候变化的影响。海洋珊瑚的光合作用共生体就是一个例子，它们在海洋变暖时被排出。关于气候对陆地系统中共生体介导的物种相互作用的影响知之甚少。独特的机会来研究这一现象发生使用易于处理的蚜虫模型与其良好的特点保护共生。蚜虫是食草昆虫和重要的农业害虫，它们携带细菌共生体，保护它们免受病原体和寄生虫的侵害。先前的工作表明，大多数广泛的抗寄生虫共生菌株在温暖的温度下无法保护蚜虫。但是这种共生体的其他菌株，以及来自第二种非必需共生体物种的菌株，在没有寄生虫的情况下为蚜虫提供了对高温的耐受性--这可能是通过拯救蚜虫生存所需的第三种共生体物种。将生物学实验与分子生物学、显微镜、基因组学和基因表达研究相结合，PI将研究温度介导的共生体失败的机制，以及共生体介导的气候适应能力的潜力。昆虫是最多样化的动物群体，大多数是共生的，因此蚜虫的发现很容易推广到大多数陆生动物。该奖项支持高中，本科，研究生研究人员的培训和专业发展，并包括社区外展活动。预测生物体对气候变化的反应是困难的，因为物种间的相互作用受到的影响不同于单个物种。更复杂的是，多细胞真核生物之间的相互作用往往是由微生物伴侣介导的，而微生物伴侣似乎特别容易受到热应激的影响。气候对微生物介导的物种相互作用的影响将使用一个高度听话的蚜虫模型系统进行研究，该系统具有在基因型和表型水平上得到良好表征的防御性共生体。先前的工作表明，大多数菌株广泛的抗寄生虫共生体，汉密尔顿，不能保护蚜虫在温暖的温度。使用来自自然种群的常见菌株，笼实验将测试以下假设：1）波动的温度维持汉密尔顿氏菌中的热相关遗传变异，而2）在没有寄生虫的情况下整体暴露于高温选择赋予热耐受性的菌株，以及3）用温暖的温度和寄生虫挑战选择提供热稳健保护的菌株。额外的分析将定义汉米尔顿功能的上限，以及另一种共生体沙雷氏菌是否在最热的地区取代汉米尔顿。为了了解共生体失败和恢复力的机制，将对相关基因组进行测序，并结合检测共生体滴度对热应激的反应、毒素的热不稳定性以及是否通过拯救专性营养共生体Buchnera而发生热耐受性的测定。该研究增强了人们对气候对昆虫普遍存在的遗传共生体的影响的理解，对所提供的许多有益服务的影响，以及对人类健康和农业的威胁。该奖项反映了NSF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。

Climate change is creating unprecedented challenges for Earth’s inhabitants. It is critical to understand how rising temperatures affect the diversity and distributions of organisms. However, predicting organismal responses to climate change is difficult, because species interactions are impacted differently than individual species. Moreover, these predictions are further complicated because species interactions often involve ‘hidden’ microbes called symbionts, which appear especially vulnerable to climate change. This is exemplified by the photosynthesizing symbionts of marine corals, which are expelled during ocean warming. Less is known about climate impacts on symbiont-mediated species interactions in terrestrial systems. Unique opportunities to study this phenomenon occur using tractable aphid models with their well-characterized protective symbioses. Aphids are plant-feeding insects and important agricultural pests, which carry bacterial symbionts that protect them against pathogens and parasites. Prior work showed that most strains of a widespread anti-parasite symbiosis failed to protect aphids at warmer temperatures. But other strains of this symbiont, and from a second non-essential symbiont species, provided aphids with tolerance to high temperatures in the absence of parasites– plausibly by rescuing a third symbiont species required for aphid survival. Combining biological experiments with molecular biology, microscopy, genomics and gene expression studies, the PIs will study mechanisms of temperature-mediated symbiont failure and, conversely, the potential for symbiont-mediated climate resilience. Insects are the most diverse animal group, and most are symbiotic, so findings from aphids readily generalize to most terrestrial animals. This award supports the training and professional development of high school, undergraduate, graduate researchers, and includes community outreach events. Predicting organismal responses to climate change is difficult because species interactions are impacted differently than individual species. A further complication is that interactions among multicellular eukaryotes are often mediated by microbial partners, which appear especially vulnerable to thermal stress. Climate impacts on microbe-mediated species interactions will be investigated using a highly-tractable aphid model system with defensive symbioses that have been well-characterized at genotypic and phenotypic levels. Prior work showed that most strains of a widespread anti-parasitoid symbiont, Hamiltonella, fail to protect aphids at warmer temperatures. Using common strains derived from natural populations, cage experiments will test hypotheses that 1) fluctuating temperatures maintain thermally-relevant genetic variation in Hamiltonella, while 2) monolithic exposure to hot temperatures without parasitoids selects for strains conferring thermal tolerance, and 3) challenge with both warm temperatures and parasitoids selects for strains providing thermally-robust protection. Additional assays will define the upper limits of Hamiltonella function, and whether another symbiont, Serratia, replaces Hamiltonella in the hottest locales. To understand mechanisms of symbiont failure and resilience, relevant genomes will be sequenced coupled with assays examining symbiont titers in response to thermal stress, heat lability of toxins, and whether thermal tolerance occurs via rescue of the obligate nutritional symbiont Buchnera. This research enhances understanding of climate impacts on the ubiquitous heritable symbioses of insects, with implications for the many beneficial services provided, and threats to human health and agriculture posed.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.