Centre for Conservation Biology, Department of Biology, Norwegian University of Science and Technology, Trondheim, Norway.
Ann Bot. 2012 Jun;109(7):1331-40. doi: 10.1093/aob/mcs091.
Most species of Dalechampia vines (Euphorbiaceae) attract bee pollinators with terpenoid resins secreted by a gland-like structure in the inflorescence. In some species, pollinating bees appear to preferentially visit inflorescences (blossoms) with large resin-producing glands, whereas in other species bees preferentially visit blossoms with large involucral bracts. In this study, the reliability of bract and gland size as signals of the quantity of resin produced in one species, D. scandens, was assessed. Whether resin secretion has a cost with respect to the number or mass of the seeds produced by a blossom was also examined.
Measurements were made of bract size, gland size and the amount of resin secreted by blossoms of D. scandens maintained in a common environment, and the relationships between these traits were analysed. Resin production was also manipulated, and the effects of the manipulation were tested on seed set and seed mass.
The amount of resin produced was better predicted by the size of the gland than by the size of the bract. Furthermore, when the effect of gland size was accounted for, bract size only weakly predicted the amount of resin produced. Neither an increase in resin secretion (by daily removal of the resin) nor a decrease (by removal of the resin gland) affected seed set or seed mass detectably, but resin production correlated positively with mean seed mass at the individual level once the size of the resin gland was accounted for.
Gland size is a better indicator of the amount of reward than bract size, although the latter remained an honest signal of the quantity of resin produced. Resin secretion has no detectable cost in terms of seed production, but may be condition dependent, as suggested by a positive correlation with seed mass at the individual level.
大多数金虎尾藤属（大戟科）藤本植物通过花序中腺体样结构分泌的萜烯树脂吸引蜜蜂传粉者。在一些物种中，传粉蜜蜂似乎更喜欢访问具有大树脂产生腺的花序（花朵），而在其他物种中，蜜蜂更喜欢访问具有大总苞片的花朵。在这项研究中，评估了大戟藤属植物 D. scandens 中苞片和腺体大小作为树脂产生量信号的可靠性。还研究了树脂分泌是否会对花朵产生的种子数量或质量产生成本。
在共同环境中对 D. scandens 的苞片大小、腺体大小和花朵分泌的树脂量进行了测量，并分析了这些特征之间的关系。还对树脂产生进行了操作，并测试了操作对结实率和种子质量的影响。
树脂产生量的预测效果优于苞片大小，腺体大小更好。此外，当考虑到腺体大小的影响时，苞片大小仅微弱地预测了树脂的产生量。树脂分泌的增加（通过每天去除树脂）或减少（通过去除树脂腺）都没有明显影响结实率或种子质量，但在考虑到树脂腺的大小后，树脂产生与个体水平的平均种子质量呈正相关。
腺体大小是奖励量的更好指标，而不是苞片大小，尽管后者仍然是树脂产生量的诚实信号。树脂分泌在种子产生方面没有可检测到的成本，但可能与条件有关，如个体水平上与种子质量呈正相关。
