Data from: What triggers colour change? Effects of background colour and temperature on the development of an alpine grasshopper

Background: Colour polymorphisms are a fascinating facet of many natural populations of plants and animals, and the selective processes that maintain such variation are as relevant as the processes which promote their development. Orthoptera, the insect group that encompasses grasshoppers and bush crickets, includes a particularly large number of species that are colour polymorphic with a marked green-brown polymorphism being particularly widespread. Colour polymorphism has been associated with the need for crypsis and background matching and background-dependent homochromy has been described in a few species. However, when and how different environmental conditions influence variation in colour remains poorly understood. Here we test for effects of background colour and ambient temperature on the occurrence of colour morph switches (green to brown or brown to green) and developmental darkening in the alpine dwelling club-legged grasshopper Gomphocerus sibiricus. Results: We monitored individually housed nymphae across three of their four developmental stages and into the first week after final ecdysis. Our data show an absence of colour morph switches in G. sibiricus, without a single switch observed in our sample. Furthermore, we test for an effect of temperature on colouration by manipulating radiant heat, a limiting factor in alpine habitats. Radiant heat had a significant effect on developmental darkening: individuals under low radiant heat tended to darken, while individuals under high radiant heat tended to lighten within nymphal stages. Young imagoes darkened under either condition. Conclusions: Our results indicate a plastic response to a variable temperature and indicate that melanin, a multipurpose pigment responsible for dark colouration and presumed to be costly, seems to be strategically allocated according to the current environmental conditions. Unlike other orthopterans, the species is apparently unable to switch colour morphs (green/brown) during development, suggesting that colour morphs are determined genetically (or very early during development) and that other processes have to contribute to crypsis and homochromy in this species.

研究背景：体色多态现象是众多动植物自然种群中极具研究价值的独特性状，维持这类变异的选择过程与推动其产生的发育过程同样具有重要意义。直翅目（Orthoptera）是涵盖蝗虫与螽斯的昆虫类群，其中包含大量体色呈多态的物种，其中显著的绿-棕体色多态尤为普遍。体色多态常与隐蔽拟态及背景匹配的需求相关联，已有少量物种被报道存在背景依赖的同色现象（homochromy）。然而，不同环境条件如何以及何时影响体色变异，目前仍知之甚少。本研究以栖息于高山生境的棒角蝗（Gomphocerus sibiricus）为研究对象，探究背景色与环境温度对其体色型转换（绿转棕或棕转绿）以及发育过程中体色加深的影响。

研究结果：我们对单只饲养的若虫进行了连续监测，覆盖其4个发育阶段中的3个阶段，直至末次蜕皮后第一周。实验数据显示，棒角蝗未发生任何体色型转换，样本中未观察到一例转换事件。此外，我们通过操控辐射热——高山生境中的关键限制因子——来探究温度对体色的影响。结果表明，辐射热对发育过程中的体色加深具有显著效应：在若虫阶段，处于低辐射热环境下的个体体色倾向于加深，而处于高辐射热环境下的个体体色则倾向于变浅；而无论环境条件如何，刚羽化的成虫体色均会加深。

研究结论：本研究结果表明体色变化存在对温度波动的表型可塑性响应，同时提示黑色素（melanin）——一种参与深色体色形成且被认为具有代谢成本的多功能色素——似乎会根据当前环境条件进行策略性分配。与其他直翅目昆虫不同，该物种显然无法在发育过程中转换体色型（绿/棕），这暗示体色型由遗传因素决定（或在发育早期即已确定），而该物种的隐蔽拟态及同色现象可能由其他机制介导。