Data from: Elucidating mechanisms for insect body size: partial support for the oxygen-dependent induction of moulting hypothesis

Body size is a key life history trait and knowledge of its mechanistic basis is crucial in life history biology. Such knowledge is accumulating in holometabolous insects, whose growth is characterised and body size affected by moulting. According to the oxygen-dependent induction of moulting (ODIM) hypothesis, moult is induced at a critical mass where oxygen demand of growing tissues overrides the supply that principally grows only at moults. Support for the ODIM hypothesis is controversial partly because of a lack of proper data to explicitly test the hypothesis. The ODIM hypothesis predicts that the critical mass is positively correlated with oxygen partial pressure (pO2) and negatively with temperature. To resolve the controversy that surrounds the ODIM hypothesis, we rigorously test these predictions by exposing penultimate-instar Orthosia gothica (Lepidoptera: Noctuidae) larvae to temperature and moderate pO2 manipulations in a factorial experiment. The relative mass increment in the focal instar increased along with increasing pO2, as predicted, but there was only weak suggestive evidence of the temperature effect. Probably due to a high measurement error in the trait, pO2 effect on the critical mass was sex-specific; high pO2 had a positive effect only in females, whereas low pO2 had a negative effect only in males. Critical mass was independent of temperature. Support for the ODIM hypothesis is partial because of only suggestive evidence of a temperature effect on moulting, but the role of oxygen in moult induction seems unambiguous. The ODIM mechanism, thus, seems worth considering in body size analyses.体型是核心生活史性状，阐明其机制基础对生活史生物学研究具有关键意义。目前学界对全变态昆虫（holometabolous insects）的相关认知正不断积累：这类昆虫的生长以蜕皮为特征，其最终体型亦受蜕皮过程调控。根据氧依赖蜕皮诱导（oxygen-dependent induction of moulting, ODIM）假说，当生长组织的氧需求超过供氧能力时，昆虫将达到临界体重并触发蜕皮——而供氧能力主要仅在蜕皮阶段得以提升。由于缺乏可直接检验该假说的合格实验数据，学界对ODIM假说的支持态度仍存在争议。 ODIM假说预测：临界体重与氧分压（oxygen partial pressure, pO2）呈正相关，与温度呈负相关。为解决围绕该假说的学术争议，本研究通过析因实验设置温度与适度氧分压的操控处理，对冬夜蛾（Orthosia gothica，鳞翅目：夜蛾科）的末前龄期（penultimate-instar）幼虫开展严格的预测验证。实验结果显示，目标龄期的相对体重增量随氧分压升高而增加，与假说预测一致，但仅能观察到微弱的温度效应暗示性证据。受该性状测量误差较高的影响，氧分压对临界体重的影响存在性别特异性：高氧分压仅对雌性个体产生正向调控效应，低氧分压仅对雄性个体产生负向调控效应；临界体重与温度无显著关联。 本研究对ODIM假说的支持效果有限，仅能观察到温度对蜕皮的暗示性影响，但氧在蜕皮诱导中的作用明确无疑。因此，在体型分析研究中，ODIM机制值得纳入考量。