BREAKDOWN: The regulation of breakdown of cooperation among species

物种之间的合作--或互惠共生--推动了生命之树上的一些最重要的创新，并为我们提供了关键的生态系统服务。虽然已经投入了大量的努力来理解互惠现象是如何产生的，但令人惊讶的是，我们对导致它们崩溃的原因知之甚少。为什么以及在什么时候，互惠关系会破裂？对失去互惠互利的物种来说，直接的进化后果是什么？我过去的研究表明，伴侣依赖程度是宏观进化层面上互惠关系崩溃的关键预测因素，兼性血统更容易被抛弃。然而，解释这种宏观进化模式的潜在机制尚不清楚。因此，我的项目的目标是测试生态过程，并揭示互惠共生崩溃的进化后果。为了实现这一点，我将利用附生茜草科植物(海藻亚科)和蚂蚁之间的互惠系统，其中包括在相当大的分支中发生的特殊数量的独立互惠破坏事件。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)和基因表达(目标2)如何对互惠共生崩溃的模拟做出反应。接下来，我们将通过追踪互惠基因工具包在新产生的基因组规模的系统发展史上的进化(目标3)，并测试相互竞争的假设，以测试互惠关系破裂的全基因组后果(目标4)，从而破译互惠互利的进化后果。通过整合方法和跨越尺度，细分将实现对为什么一些谱系放弃互惠制度以及这将带来什么进化后果的预测性理解。理解互惠关系的崩溃对于解释自然界中互惠关系的流行和预测依赖于它们的许多系统的潜在崩溃条件都是至关重要的。

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.