BREAKDOWN: The regulation of breakdown of cooperation among species

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Cooperation among species -or mutualism- has driven some of the most important innovations across the tree of life, and provide us with key ecosystem services. While a great deal of effort has been put into understanding how mutualisms arise, we know surprisingly little of what leads to their breakdown. Why and when do mutualism break down? What are the direct evolutionary consequences for species that lose mutualism? My past research revealed that the level of partner dependence is a key predictor of mutualism breakdown at the macroevolutionary scale, with facultative lineages being more vulnerable to abandonment. Yet, the underlying mechanisms explaining this macroevolutionary pattern are unknown. The goal of my project, therefore, is to test the ecological processes and reveal the evolutionary consequences of mutualism breakdown. To achieve this, I will capitalize on the mutualistic system between epiphytic Rubiaceae plants (Hydnophytinae) and ants, which involves an exceptional number of independent mutualism breakdown events in a sizeable clade. My team will first experimentally test how physiology and traits (Aim 1) and gene expression (Aim 2) in facultative vs. obligate species respond to simulations of mutualism breakdown. Next, we will decipher the evolutionary consequences of mutualism breakdown, by tracing the evolution of the mutualistic gene toolkit across a newly generated genome-scale phylogeny (Aim 3), and test competing hypotheses underlying the genome-wide consequences of mutualism breakdown (Aim 4). By integrating approaches and crossing scales, BREAKDOWN will achieve a predictive understanding of why some lineages abandon mutualisms, and what evolutionary consequences this bears. Understanding mutualism breakdown is critical to both explaining the prevalence of mutualisms in the natural world and predicting the conditions for potential collapse of the many systems that rely upon them.