Milkweed trait values associated with aridity gradients and drought-induced changes in hostplant quality

The response of herbivorous insects to plant drought stress can
range from positive to negative, and it has been challenging to understand
the causes of this variation. We tested whether plant trait values
associated with aridity gradients might underlie this variation and how
effects vary among two insect-feeding guilds. Here we propose that plant
trait values associated with adaptation to arid environments would result
in positive effects of experimental drought on herbivores, with such plant
species adaptively shifting resources away from resistance to maintain
performance under stress. In contrast, plants with trait values associated
with adaptation to mesic environments would result in negative effects of
drought because such species lose vigor and thus decline in their
host-quality. We tested these predictions using experimental manipulations
in 13 milkweed species (genus Asclepias) adapted to a wide range
of environmental conditions, and herbivore performance of herbivores. We
exposed plants to species-specific watering regimes physiologically
calibrated to maximize (100%) or reduce (50%) stomatal conductance and
then monitored the performance of the herbivores. Here we present milkweed
trait values associated with aridity gradient [specific leaf area (SLA),
relative water content (RWC), water use efficiency (WUE), and maximum
stomatal conductance (gsmax)] and changes of trait values associated with
host-plant quality to herbivores [nutrients content (protein, nitrogen,
and carbohydrates) and plant defensive traits(latex and
cardenolides)].

植食性昆虫对植物干旱胁迫的响应可呈现从正向到负向的连续谱系，解析该响应差异的成因长期以来都是学界的挑战性课题。我们探究了与干旱梯度相关的植物性状值是否为该响应差异的核心驱动因素，同时验证了这种效应在两类昆虫取食功能群间的变化模式。本研究提出，适应干旱环境的植物类群，其相关性状会使实验性干旱对植食性昆虫产生正向效应——这类植物会通过适应性资源重分配，将原本用于防御的资源转向维持自身在胁迫环境下的生理表现。与之相反，适应湿润环境的植物类群则会让干旱产生负向效应：这类物种在干旱胁迫下会丧失生长活力，进而导致其作为昆虫寄主的品质下降。我们通过操控实验验证了上述预测：实验材料为13种适应多样环境条件的马利筋属（Asclepias）植物，检测指标为植食性昆虫的生长表现。我们为每种植物设置了专属的浇水方案，该方案通过生理校准分别实现气孔导度最大化（100%）或降低50%，随后持续监测植食性昆虫的生长表现。本数据集包含与干旱梯度相关的马利筋性状数据[比叶面积（specific leaf area, SLA）、相对含水量（relative water content, RWC）、水分利用效率（water use efficiency, WUE）以及最大气孔导度（maximum stomatal conductance, gsmax）]，以及与植食性昆虫寄主品质相关的性状变化数据[营养成分（蛋白质、氮素与碳水化合物）以及植物防御性状（乳汁与强心苷）]。