Data from: Evidence for the adaptive significance of secondary compounds in vertebrate-dispersed fruits

Although the primary function of fleshy fruits is to attract seed dispersers, many ripe fruits contain toxic secondary compounds. A number of hypotheses have been proposed to explain this evolutionary paradox, most of which describe the potential adaptive role secondary compounds may play in seed dispersal. However, some authors have argued that fruit secondary compounds may be non-adaptive, and instead explain their occurrence as a pleiotropic consequence of selection for defense of leaves and other tissues. We address these alternative evolutionary hypotheses through a comparative examination of iridoid glycosides in leaves, unripe fruits, and ripe fruits of Lonicera x bella (Belle's bush honeysuckle), combined with an examination of fruit damage and removal in natural populations. We provide several lines of evidence that fruit secondary compounds cannot be explained solely as a consequence of foliar defense, including higher concentrations and more individual compounds in fruits compared to leaves and a negative relationship between iridoid glycoside concentration and fruit damage. However, we also show that the composition and concentrations of secondary compounds in leaves and fruits are not entirely independent, emphasizing that selection in different plant parts is intrinsically linked. We conclude that the adaptive significance of chemical traits is best considered in a whole-plant context that includes fruit-frugivore interactions.尽管肉质果实的核心功能是吸引种子传播者，但许多成熟果实中仍含有有毒次生代谢物。学界已提出多种假说以解释这一进化悖论，其中多数假说阐述了次生代谢物在种子传播过程中可能发挥的潜在适应性功能。然而，部分学者认为果实中的次生代谢物并非适应性演化的产物，而是叶片及其他组织防御功能演化所带来的多效性结果。本研究通过对贝氏忍冬（Lonicera x bella，又名贝尔灌丛忍冬）的叶片、未成熟果实及成熟果实中的环烯醚萜苷（iridoid glycosides）开展比较分析，并结合对自然种群中果实受损与被移除情况的调查，对这两种对立的演化假说进行了验证。本研究提供了多组证据表明，果实次生代谢物无法仅通过叶片防御的演化结果来解释：相较于叶片，果实中的次生代谢物浓度更高、单体化合物种类更多，且环烯醚萜苷浓度与果实受损程度呈负相关关系。但本研究同时发现，叶片与果实中的次生代谢物组成及浓度并非完全独立，这说明不同植物组织所受的选择压力存在内在关联。综上，我们认为植物化学性状的适应意义应在整株植物的框架下进行考量，其中需纳入果实与食果动物的相互作用这一维度。