Data from: Body size response to warming: time of the season matters in a tephritid fly

Whether shrinking body size is a universal response to climate change remains controversial. Here, assuming that life history traits evolve to maximize fitness according to life history plasticity theory, we hypothesized that under global warming temperate multivoltine insects should emerge earlier with a smaller body mass in the early growing season, but emerge later with a larger body mass in the late season. We tested this hypothesis by conducting two field artificial warming experiments in an alpine meadow: 1) with one pre-dispersal seed predator species (Tephritis femoralis) and its two host plant species flowering in early and late growing seasons, respectively, and 2) with the tephritid flies and one host species with a flowering season that occupies parts of both the early and late growing seasons. These experiments were complemented by a microcosm chamber warming experiment, in which increasing and decreasing temperature trends were set to simulate temperature variation pattern in early and late growing seasons, respectively, but photoperiod was held constant. Warming generally advanced the adult emergence and decreased the body size (adult body mass) in the early season but delayed the emergence and increased the size in the late season in both field experiments, indicating that the seasonally different effects of warming on the fly body size was constant regardless of host plant identity. The chamber warming resulted in consistent responses of emerging timing and body size to the simulated seasonal warming, demonstrating that the temperature increase per se and its interaction with direction of temperature change, but not other correlated effects, should be primarily responsible for the observed contrasting shifts of body size at different times of the season. Our results indicate that taking into account temperate seasonal patterns of temperature variation could be of general importance for predicting animal body size changes in the warmed future.体型缩小是否为气候变化下的普遍响应，目前仍存在争议。本研究基于生活史可塑性理论（life history plasticity theory），假设生活史特征（life history traits）的演化以最大化适合度（fitness），据此提出假说：在全球变暖背景下，温带多化性昆虫（temperate multivoltine insects）应在生长季早期更早羽化且体型更小，而在生长季晚期更晚羽化且体型更大。我们在高寒草甸开展了两项田间人工增温实验以验证该假说：其一，以一种扩散前种子捕食者——菊泉蝇（Tephritis femoralis）及其两种分别在生长季早期和晚期开花的寄主植物为研究对象；其二，以实蝇类昆虫及一种开花时段覆盖生长季早、晚期部分时段的寄主植物为研究对象。本研究还辅以一项微宇宙培养箱（microcosm chamber）增温实验，该实验分别设置升温和降温温度趋势，以模拟生长季早期和晚期的温度变化模式，同时保持光周期恒定。两项田间实验均显示，增温总体上使生长季早期的成虫羽化时间提前、体型（成虫体重，adult body mass）减小，而使生长季晚期的羽化时间推迟、体型增大，这表明无论寄主植物种类如何，增温对昆虫体型的季节特异性影响均保持一致。培养箱增温实验中，成虫羽化时间与体型对模拟季节增温的响应趋势一致，这表明：观测到的季节不同时段体型的反向变化，主要是由温度升高本身及其与温度变化方向的交互作用所致，而非其他相关联效应。本研究结果表明，考虑温带地区温度变化的季节模式，对于预测气候变暖背景下动物体型的变化具有普遍重要意义。