Data from: Three's a crowd: trade-offs between attracting pollinators and ant bodyguards with nectar rewards in Turnera

Many plants attract insect pollinators with floral nectar (FN) and ant “bodyguards” with extrafloral nectar (EFN). If nectar production is costly or physiologically linked across glands, investment in one mutualism may trade off with investment in the other. We confirmed that changes in FN and EFN availability alter pollination and ant defense mutualisms in a field population of Turnera ulmifolia. Plants with additional FN tended to produce more seeds, while plants with reduced EFN production experienced less florivory. We then mimicked the consumptive effects of mutualists by removing FN or EFN daily for 50 days in a full factorial design using three Turnera species (T. joelii, T. subulata, and T. ulmifolia) in a glasshouse experiment. For T. ulmifolia and T. subulata, but not T. joelii, removing either nectar reduced production of the other, showing for the first time that EFN and FN production can trade off. In T. subulata, increased investment in FN decreased seed set, suggesting that nectar production can have direct fitness costs. Through the linked expression of EFN and FN, floral visitors may negatively affect biotic defense, and extrafloral nectary visitors may negatively affect pollination.多数植物通过花蜜（floral nectar, FN）吸引昆虫传粉者，并通过花外蜜（extrafloral nectar, EFN）吸引蚂蚁作为“护卫者”。若蜜腺分泌存在代谢成本，或不同腺体间存在生理关联，则对一种互利共生关系的投入，可能与对另一种的投入形成权衡。本研究首先在野外种群的黄香时钟花（Turnera ulmifolia）中证实，调整FN与EFN的可获得性，会改变其传粉与蚂蚁防御两类互利共生关系：额外添加FN的植株往往结出更多种子，而EFN分泌量降低的植株则遭受更少的花部植食危害。随后，本研究在温室实验中采用完全析因设计，针对3种时钟花属（Turnera）植物（T. joelii、T. subulata与T. ulmifolia），通过每日移除FN或EFN的方式模拟互利共生者的消耗效应，实验周期为50天。针对T. ulmifolia与T. subulata（而非T. joelii），移除任意一种蜜腺分泌物均会降低另一种的分泌量，这首次证实了EFN与FN的分泌存在权衡关系。在T. subulata中，FN投入的增加会降低结籽率，表明蜜腺分泌确实会直接产生适合度成本。基于EFN与FN分泌的生理关联，传粉昆虫的造访可能会对植物的生物防御产生负面影响，而花外蜜腺访客则可能抑制植物的传粉过程。