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. Moreover, the mechanisms underlying body size shifts are poorly understood. 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 (tephritid flies, 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性响应，目前尚存争议。此外，体型变化背后的潜在机制尚未得到充分阐释。本研究基于生活史可塑性理论（life history plasticity theory），假设生活史性状（life history traits）会朝着最大化适合度（fitness）的方向演化，据此提出假说：全球变暖背景下，温带多化性昆虫在生长季早期会提前羽化且体质量更小，而在生长季晚期则会推迟羽化且体质量更大。我们通过在高寒草甸开展两项野外人工增温实验验证该假说：其一，以一种扩散前种子捕食者——实蝇（tephritid flies，*Tephritis femoralis*）及其两种寄主植物为研究对象，两种寄主植物分别在生长季早期和晚期开花；其二，以该实蝇和一种寄主植物为研究对象，该寄主植物的花期覆盖生长季早晚期的部分时段。本研究还辅以一项微宇宙培养箱增温实验：该实验分别设置温度上升和下降趋势，以模拟生长季早晚期的温度变化模式，同时保持光周期（photoperiod）恒定。两项野外实验均显示，增温在生长季早期普遍提前了成虫羽化时间并降低了成虫体质量（成虫体重），而在生长季晚期则推迟了羽化时间并增大了体质量，这表明无论寄主植物种类如何，增温对实蝇体质量的季节效应均保持一致。微宇宙培养箱增温实验中，成虫羽化时间和体质量对模拟季节增温的响应结果一致，这表明：是温度升高本身及其与温度变化方向的交互作用，而非其他相关效应，是导致不同季节下体质量出现相反变化趋势的主要原因。本研究结果表明，考虑温带地区温度变化的季节模式，对于预测未来变暖背景下动物体质量的变化具有普遍的重要意义。