Ontogenetic shift from aposematism and gregariousness to crypsis in a Romaleid grasshopper - dataset

Traits of chemically-defended animals can change as an individual grows and matures, and both theoretical and empirical evidence favour a direction of change from crypsis to aposematism. This study examines the suite of traits involved in an unusual opposite shift from aposematism to crypsis in a neotropical toxic-plant-feeding Romaleid grasshopper, Chromacris psittacus (Gerstaecker, 1873). Field surveys, behavioural observations and a rearing experiment compare host plant choice, aggregation, locomotion and thermoregulation between life history stages. Results showed that both nymphs and adults fed exclusively on a narrow range of Solanaceae plants, suggesting that the shift in defensive syndrome is not due to a change in chemical defense. Instead, nymphal aposematism appears linked to aggregation in response to plant-based selection pressures. Slow nymphal development suggests a cost to feeding on toxic plant compounds, and grouping could mitigate this cost. Grouping also increases conspicuousness, and hence can favour warning colourating in chemically-defended insects. The role of diet breadth in aposematism is poorly understood, and these results suggest how constraints imposed by feeding on toxic plants can generate bottom-up selection pressures shaping the adaptive suites of traits of chemically-defended animals.

化学防御性动物的特性会随着个体的生长和成熟而发生改变，理论及实证证据均倾向于支持其防御策略从隐匿性向警示性的转变趋势。本研究旨在探讨新热带地区有毒植物食性蝗虫 Romaleid grasshopper Chromacris psittacus（Gerstaecker，1873）在从警示性向隐匿性这一罕见逆向转变中所涉及的特性组合。通过野外调查、行为观察以及饲养实验，本研究对比了不同生命阶段的主食植物选择、聚群行为、运动能力和体温调节。研究结果表明，若虫和成虫均专一地以狭小的茄科植物为食，这表明防御综合征的转变并非由于化学防御的改变。相反，若虫的警示性似乎与对植物选择压力的聚群反应有关。若虫缓慢的生长速度暗示了食用有毒植物化合物的代价，而聚群行为则可能减轻这一代价。聚群行为也增加了显著度，从而可能有利于化学防御昆虫的警示色彩。在警示性中饮食范围的作用尚不明确，而本研究揭示了通过食用有毒植物所施加的约束如何从底层产生选择压力，进而塑造化学防御动物的适应性特性组合。