Data from: Eco-evolutionary theory and insect outbreaks

Eco-evolutionary theory argues that population cycles in consumer-resource interactions are partly driven by natural selection, such that changes in densities and changes in trait values are mutually reinforcing. Evidence that the theory explains cycles in nature, however, is almost nonexistent. Experimental tests of model assumptions are logistically impractical for most organisms, while for others, evidence that population cycles occur in nature is lacking. For insect baculoviruses in contrast, tests of model assumptions are straightforward, and there is strong evidence that baculoviruses help drive population cycles in many insects, including the gypsy moth that we study here. We therefore used field experiments with the gypsy moth baculovirus to test two key assumptions of eco-evolutionary models of host-pathogen population cycles: that reduced host infection risk is heritable and that it is costly. Our experiments confirm both assumptions, and inserting parameters estimated from our data into eco-evolutionary insect-outbreak models gives cycles closely resembling gypsy moth outbreak cycles in North America, whereas standard models predict unrealistic stable equilibria. Our work shows that eco-evolutionary models are useful for explaining outbreaks of forest insect defoliators, while widespread observations of intense selection on defoliators in nature and of heritable and costly resistance in defoliators in the lab together suggest that eco-evolutionary dynamics may play a general role in defoliator outbreaks.生态进化理论（Eco-evolutionary theory）指出，消费者-资源相互作用中的种群周期波动，部分由自然选择驱动，即种群密度变化与性状值变化之间存在相互强化的关联。然而，目前几乎没有证据表明该理论能够解释自然界中的此类周期现象。对多数生物而言，验证模型假设的实验在实操层面难以开展；而对其余生物来说，也缺乏其种群周期存在于自然界的相关证据。相较之下，昆虫杆状病毒（insect baculovirus）的模型假设验证则较为简便，且已有充分证据表明，杆状病毒会推动多种昆虫的种群周期波动，其中便包括本研究聚焦的舞毒蛾（gypsy moth）。因此，本研究借助舞毒蛾杆状病毒的野外实验，验证了宿主-病原体种群周期波动生态进化模型的两项核心假设：宿主感染风险降低的性状具备可遗传性，且该性状存在适应性代价。本实验证实了这两项假设；将本研究数据估算得到的参数代入生态进化式昆虫暴发模型后，模拟得到的周期波动与北美地区舞毒蛾暴发周期高度吻合，而传统模型则会预测出不符合实际的稳定平衡状态。本研究表明，生态进化模型可有效解释森林食叶昆虫的暴发现象；而学界在自然界中观测到食叶昆虫承受强烈选择压力、在实验室中发现食叶昆虫的抗性具备可遗传性且存在适应性代价的相关报道广泛存在，这些结果共同暗示，生态进化动力学或许在食叶昆虫暴发过程中发挥着普遍作用。