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）提出，消费者-资源相互作用中的种群周期部分由自然选择驱动，即种群密度变化与性状值变化呈相互增强的关联。然而，目前几乎尚无证据表明该理论可解释自然界中的种群周期现象。对多数生物而言，模型假设的实验验证在实际操作中难以实现；而对于其余类群，也缺乏其种群周期在自然界中存在的相关证据。与之形成鲜明对比的是，昆虫杆状病毒（baculovirus）的模型假设检验流程简便，且已有充分证据显示，杆状病毒可驱动包括本研究聚焦的舞毒蛾（gypsy moth）在内的多种昆虫的种群周期。为此，我们依托舞毒蛾杆状病毒开展野外实验，对宿主-病原体种群周期生态进化模型的两项核心假设进行检验：一是宿主感染风险降低的性状可遗传，二是该性状存在适应性代价。实验结果证实了这两项假设；将本研究数据估算得到的参数代入生态进化型昆虫暴发模型后，模拟得到的种群周期与北美地区舞毒蛾暴发周期高度吻合，而标准模型则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（defoliators）的暴发现象；结合自然界中针对食叶昆虫的强烈选择观测结果，以及实验室中发现的食叶昆虫可遗传且具有代价的抗性证据，共同提示生态进化动力学可能在食叶昆虫暴发过程中发挥普遍作用。