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（consumer-resource interactions）中的种群循环部分由自然选择驱动，即种群密度变化与性状值变化相互增强。然而，几乎没有证据表明该理论能够解释自然界中的种群循环。对多数生物而言，模型假设的实验检验在实操层面不可行；而对另一些生物来说，又缺乏其种群循环在自然界中存在的佐证。与之相对，对于昆虫杆状病毒（baculovirus）而言，模型假设的检验简单易行，且有充分证据表明杆状病毒会推动多种昆虫的种群循环，包括我们本次研究的舞毒蛾（gypsy moth）。因此，我们借助舞毒蛾杆状病毒开展野外实验，以检验寄主-病原种群循环（host-pathogen population cycles）生态进化模型的两项核心假设：一是寄主感染风险降低具有可遗传性，二是该抗性存在适应性代价。本实验证实了这两项假设；将从我们的数据中估算得到的参数（parameters）代入昆虫暴发模型后，得到的种群循环与北美地区舞毒蛾的暴发循环高度相似，而标准模型则预测出不符合现实的稳定平衡状态。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；而自然界中针对食叶昆虫的强烈选择、实验室中观测到的食叶昆虫可遗传且具代价的抗性这两类现象广泛存在，共同暗示生态进化动力学可能在食叶昆虫暴发中发挥普遍作用。