Ants and plants that depend on each other for survival are abandoning their partnerships, and no one fully understands why. Mutualisms—where two species cooperate for mutual benefit—underpin many of the ecosystems humans rely on, from pollination to nutrient cycling. Yet most research focuses on how these partnerships form, not why they fall apart. This project targets that blind spot. The researcher has already shown that species with flexible, non-obligate partnerships are more likely to abandon mutualism over evolutionary time, but the mechanisms driving that pattern remain unknown. This is fundamental science. It will not produce a new battery or a crop treatment. What it could change is how ecologists predict the stability of ecosystems under stress. If researchers can identify the physiological, genetic, and evolutionary conditions that trigger mutualism breakdown, they may eventually forecast which species or systems are most vulnerable to collapse—knowledge that matters for conservation, agriculture, and climate adaptation. Past fundamental work on mutualism has already reshaped how we manage pollination networks and soil microbiomes; this project extends that logic to the moment cooperation ends.
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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.
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