CAREER: The ontogeny of mutualism: exploring variation in costs and benefits within an ant-plant symbiosis

互惠，即物种之间的合作互动，是地球上最广泛的物种互动之一。从为植物伙伴获取养分的微小真菌，到传播林木种子的大型哺乳动物，再到维持全球农业生产力的传粉者，互惠伙伴关系在全球经济和维持生物多样性方面发挥着核心作用。一个关键的悬而未决的问题是，当自然选择应该有利于那些在不支付合作成本的情况下获得好处的自私个体时，这些互动如何保持合作？解决这一问题的研究通常会计算与特定伙伴物种互动的成本和收益，而不考虑个人的生命阶段以及与其他伙伴物种的互动。但自然选择影响一生的健康，许多互助者在他们的一生中与多个伙伴物种互动。评估多种伙伴关系的成本和收益如何在互助者的一生中整合，是理解这些全球重要互动如何演变和发挥作用的关键环节。这项研究集中在东非发现的一种多物种蚂蚁-植物(相思树)互惠共生，试图评估互惠共生的成本和收益如何随着相互作用伙伴物种的生命阶段的变化而变化，以及多重相互作用的净适合度效应如何随着植物与不同蚂蚁物种伙伴关系的时间、持续时间和顺序的变化而变化。这一结果将揭示这种互惠模式如何保持合作，以及哪些因素可以加速其崩溃。这项研究还将涉及制定四个协同教育目标，旨在吸引美国和非洲本科生、K-12学生和普通公众参与。该项目将开发一个为期一个月的实地项目，直接让美国本科生参与原创研究和体验式学习，并允许从植物和动物的角度对优秀的本科生进行互惠共生生态方面的培训。此外，通过与一名非洲合作者合作，该项目每年将把25名肯尼亚K-12学生带到实地，了解东非的自然历史，使用蚂蚁-相思系统积极让孩子们参与科学发现的过程。

Mutualisms, cooperative interactions among species, are among the most widespread species interactions on earth. From tiny fungi that harvest nutrients for their plant partners, to large mammals that disperse the seeds of forest trees, to the pollinators that maintain global agricultural productivity, mutualistic partnerships play a central role in the global economy and the maintenance of biological diversity. A key unresolved question is, how do these interactions remain cooperative when natural selection should favor selfish individuals who reap benefits without paying the costs of cooperation? Studies addressing this question typically calculate the costs and benefits of interacting with a given partner species independent of an individual's life stage and interactions with other partner species. But natural selection acts on lifetime fitness, and many mutualists interact with multiple partners species throughout their lives. Evaluating how the costs and benefits of multiple partnerships integrate over the lifetime of mutualists is a critical link in understanding how these globally important interactions evolve and function. Focusing on a multi-species ant-plant (Acacia) mutualism found throughout East Africa, this study seeks to evaluate how the costs and benefits of mutualism change with variation in the life-stage of interacting partner species, and how the net fitness effects of multiple interactions change with variation in the timing, duration and sequence of plant partnerships with different ant species. The results will shed light on how this model mutualism remains cooperative, and what factors can precipitate its breakdown. This research will also involve the development of four synergistic educational objectives aimed at engaging U.S. and African undergraduate students, K-12 students, and the general public. The program will develop a month-long field program that directly engages U.S. undergraduate students in original research and experiential learning, and allow for the training of exceptional undergraduates in the ecology of mutualism from both plant and animal perspectives. In addition, by partnering with an African collaborator, the program will bring 25 Kenyan K-12 students to the field site each year to learn about the natural history of East Africa, using the ant-Acacia system to actively engage kids in the process of scientific discovery.