Interspecific difference in prey captures.

Sarracenia pitcher plants display interspecific differences in prey, so far only explained by pitcher morphology. We hypothesized that pitcher odours play a role in prey composition. We first compared odour and prey compositions among Sarracenia taxa grown together, forming a kinship gradient from S. purpurea known to capture primarily ants towards S. leucophylla known to capture many flying insects: S. purpurea, S. X mitchelliana, and S. X Juthatip soper & S. X leucophylla horticultural hybrids. We then measured several pitcher traits to disentangle the contributions of morphology and odour to prey variation. The pitcher odours were as diverse as those of generalist-pollinated flowers but with notable differences among taxa, reflecting their relatedness. VOC similarity analyses revealed taxon specificities, that mirrored those revealed by prey similarity analyses. S. X leucophylla stood out by being more specialised in flying insects like bees and moths and by releasing more monoterpenes known to attract flower visitors. S. X Juthatip soper trapped as many bees but fewer moths, sesquiterpenes contributing less to its scent. Ants and Diptera were the main prey of the other two with fatty-acid-derivative-dominated scents. Quantities of the different prey groups can be inferred 98% from quantities of the odour classes and pitcher dimensions. Two syndromes were revealed: ants associated with fatty-acid-derivatives and short pitchers; flying insects associated with monoterpenes, benzenoids and tall pitchers. In S. X leucophylla, emission rate of fatty-acid-derivatives and pitcher length explained most variation in ant captures; monoterpenes and pitcher length explained most variation in bee and moth captures; monoterpenes alone explained most variation in Diptera and wasp captures. Our results suggest that odours are key factors of the diet composition of pitcher plants. They support the hypothesis of perceptual exploitation of insect biases in carnivorous plants and provide new insights into the olfactory preferences of insect groups.瓶子草属（Sarracenia）植物的猎物组成存在种间差异，目前仅能通过瓶状体形态学特征予以解释。我们提出假说：瓶状体释放的挥发性气味在猎物组成的塑造中发挥关键作用。本研究首先对共同栽培的瓶子草类群的气味与猎物组成进行比较，这些类群构成一条亲缘梯度：从主要捕获蚂蚁的紫瓶子草（S. purpurea），到偏好捕获大量飞行昆虫的白瓶子草（S. leucophylla），涉及类群包括S. purpurea、S. × mitchelliana，以及园艺杂交种S. × Juthatip soper与S. × leucophylla。随后，我们测定了多项瓶状体性状，以解析形态学特征与气味信号对猎物组成变异的相对贡献。瓶状体释放的气味与泛化传粉植物的花朵气味同样多样，但类群间存在显著差异，且与其亲缘关系相契合。挥发性有机化合物（Volatile Organic Compounds, VOC）相似性分析揭示了类群特异性，该结果与猎物组成相似性分析得到的结论一致。S. × leucophylla表现出独特的特征：其更特化于捕获蜜蜂、蛾类等飞行昆虫，且释放更多已知可吸引花部访客的单萜类化合物。S. × Juthatip soper捕获的蜜蜂数量与其余类群相当，但蛾类捕获量更少，其气味中倍半萜类化合物占比更低。其余两个类群的主要猎物为蚂蚁与双翅目（Diptera）昆虫，其气味以脂肪酸衍生物为主。通过气味类别与瓶状体尺寸的量化数据，可98%准确推断不同猎物类群的种群数量。本研究揭示了两类协同特征组合：一类为蚂蚁关联脂肪酸衍生物与短瓶状体；另一类为飞行昆虫关联单萜、苯类化合物与高瓶状体。在S. × leucophylla中，脂肪酸衍生物的释放量与瓶状体长度可解释蚂蚁捕获量的大部分变异；单萜类化合物与瓶状体长度可解释蜜蜂与蛾类捕获量的大部分变异；仅单萜类化合物即可解释双翅目昆虫与胡蜂捕获量的大部分变异。本研究结果表明，气味是瓶子草属植物猎物组成的关键影响因素。研究结果支持食肉植物通过感知利用昆虫行为偏爱的假说，并为解析不同昆虫类群的嗅觉偏好提供了全新视角。