LTREB: COLLABORATIVE RESEARCH: Host-microbe symbiosis through the lens of stochastic demography

几乎所有的植物和动物都含有微生物，比如生活在它们上面或里面的细菌。了解这些微生物对寄主物种的影响可能会提高我们解决农业、野生动物疾病和人类健康问题的能力。在完全实现这些应用之前，生物学家首先需要更好地了解微生物何时以及如何影响宿主的适应性。这个项目将测试这样一个假设，即微生物对宿主的影响每年都会波动，在压力较大的年份(宿主需要帮助)是有益的，但在有利的年份是中性的或代价高昂的。因此，与没有微生物的宿主相比，有微生物的宿主的健康状况每年的波动可能会更小，这可能是容纳微生物的一个重要好处。这一假设将通过扩展对含有真菌微生物的草物种的长期田间试验的数据收集，在该试验中收集关于草的遗传学的新数据，并应用统计建模方法来检验。生活在植物内的真菌微生物广泛存在于牧草中，包括对牲畜很重要的饲草草，这项研究可能会有重要的农业应用。此外，该项目将为高中、本科生和研究生水平的学生提供研究培训。共生宿主中人口统计学差异减少的假设导致了两个新的预测，该项目旨在测试这两个预测。首先，通过缓冲宿主免受恶劣条件的影响，共生体可能会限制遗传漂移，并促进宿主种群中更高的遗传多样性。其次，有共生体和无共生体的宿主在其种群速率上可能表现出不同的时间波动模式，从而促进了储存效应，这一机制可以稳定共生和不共生宿主的竞争共存，并潜在地解释了在各种动植物共生体中广泛观察到的宿主类型的混合。该科学团队将使用德克萨斯州和印第安纳州的长期田间实验来验证这些预测，在这些实验中，草种群被建立在有或没有真菌内生菌的情况下。基于九年的人口统计数据并利用分层贝叶斯分析框架，该团队将通过减少方差和对平均性能的影响来量化和比较共生对宿主适应性的影响，并测试储存效应对有无共生的宿主共存的贡献。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。

Nearly all plants and animals harbor microbes such as bacteria that live on or in them. Understanding the influence of these microscopic organisms on their host species may advance our ability to solve problems in agriculture, wildlife disease, and human health. Before these applications can be fully realized, biologists first require a better understanding of when and how microbes influence the fitness of their host. This project will test the hypothesis that the effects of microbes on their hosts fluctuate from year to year, being beneficial in stressful years (when hosts need assistance) but neutral or costly in favorable years. As a consequence, hosts with microbes may experience reduced year-to-year fluctuation in fitness compared to hosts without microbes, which may be an important benefit of harboring microbes. This hypothesis will be tested by extending data collection of a long-term field experiment with grass species that harbor fungal microbes, collecting new data on the genetics of the grasses in that experiment, an applying a statistical modeling approach. Fungal microbes that live inside plants are a widespread in grasses, including forage grasses that are important to livestock, and this research could have important agricultural applications. Additionally, this project will provide research training for students at the high school, undergraduate, and graduate levels.The hypothesis of reduced demographic variance in symbiotic hosts leads to two novel predictions that this project is designed to test. First, by buffering hosts against harsh conditions, symbionts may limit genetic drift and promote higher genetic diversity in host populations. Second, hosts with and without symbionts may exhibit different patterns of temporal fluctuation in their demographic rates, thus promoting the storage effect, a mechanism that can stabilize competitive coexistence of symbiotic and symbiont-free hosts, and potentially explain the mixtures of host types that are widely observed in a diversity of plant and animal symbioses. The scientific team will test these predictions using a long-term field experiment with sites in Texas and Indiana, in which grass populations were established with or without fungal endophytes. Building on nine years of demographic data and leveraging a hierarchical Bayesian analytical framework, the team will quantify and compare the effects of symbiosis on host fitness via reductions in variance versus effects on mean performance, and test the contributions of the storage effect to the coexistence of hosts with and without symbionts.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.