BREAKDOWN: The regulation of breakdown of cooperation among species

物种之间的合作——或互惠共生——推动了生命之树上一些最重要的创新，并为我们提供了关键的生态系统服务。尽管人们付出了大量的努力来理解共生关系是如何产生的，但令人惊讶的是，我们对导致共生关系破裂的原因知之甚少。互惠主义为何以及何时会崩溃？失去共生关系的物种在进化上的直接后果是什么？我过去的研究表明，伴侣依赖水平是宏观进化尺度上互惠关系破裂的关键预测因素，兼性谱系更容易被抛弃。然而，解释这种宏观进化模式的潜在机制尚不清楚。因此，我的项目目标是测试生态过程，揭示共生关系崩溃的进化后果。为了实现这一点，我将利用附生Rubiaceae植物（水螅科）和蚂蚁之间的共生系统，这涉及到一个相当大的进化分支中大量独立的共生崩溃事件。我的团队将首先通过实验测试兼性物种和专性物种的生理和特征（目标1）以及基因表达（目标2）对共生关系崩溃模拟的反应。接下来，我们将通过在新产生的基因组级系统发育中追踪互惠基因工具包的进化来破译互惠崩溃的进化后果（目标3），并测试互惠崩溃的全基因组后果背后的相互竞争的假设（目标4）。通过整合方法和跨越尺度，BREAKDOWN将获得对为什么一些谱系放弃互惠关系的预测性理解，以及这将带来什么样的进化后果。理解共生关系的崩溃对于解释自然界中共生关系的普遍存在以及预测依赖于它们的许多系统可能崩溃的条件至关重要。

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.