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.

体型是生命史研究中的关键性状，阐明其机制基础对生命史生物学而言至关重要。相关研究在全变态昆虫（holometabolous insects）中持续积累，这类昆虫的生长以蜕皮为核心特征，其体型亦受蜕皮过程调控。氧依赖蜕皮诱导（oxygen-dependent induction of moulting, ODIM）假说提出，当生长组织的氧需求超过供氧能力时，昆虫将达到临界体型并启动蜕皮，而供氧主要仅在蜕皮周期内得以提升。目前学界对ODIM假说的支持尚存争议，部分原因在于缺乏可明确检验该假说的恰当实验数据。ODIM假说预测，临界体型与氧分压（oxygen partial pressure, pO2）呈正相关，与温度呈负相关。为厘清围绕ODIM假说的学术争议，我们采用析因实验设计，设置温度与适度pO2调控处理，对末前龄的灰夜蛾（Orthosia gothica，鳞翅目：夜蛾科）幼虫开展严格实验以检验上述预测。正如假说预期，目标观测龄期的相对体重增量随pO2升高而增加，但仅能得到温度效应的微弱提示性证据。该性状可能因测量误差较大，导致pO2对临界体型的效应呈现性别特异性：高pO2仅对雌性个体产生正向效应，而低pO2仅对雄性个体产生负向效应。临界体型与温度无关。由于仅能得到温度对蜕皮效应的提示性证据，本研究对ODIM假说的支持尚不充分，但氧在蜕皮诱导中的作用似乎明确无疑。因此，在体型分析中值得纳入ODIM机制予以探讨。