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

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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.