Functional specialization and phenotypic generalization in the pollination system of an epiphytic cactus

ABSTRACT Plant-pollinator interactions range from obligatory specialists to facultative generalists, and floral morphology and pollination system may not match completely. The floral biology, reproductive system and floral visitors of a species of the tribe Rhipsalideae were investigated with a focus on the consistency between the pollination system and the floral phenotype. Rhipsalis neves-armondii is an obligate xenogamous species, due to self-sterility. Its flowers are white, small and diurnal, and radially symmetrical. These features, along with their small amount of nectar, characterize the flowers as phenotypic generalists. The most frequent pollinators were a solitary oligolectic species of Andrenidae (Rhophitulus solani), two species of Meliponinae (Trigona spinipes and T. braueri) and Apis mellifera. Despite the generalist floral phenotype, the pollination system is functionally specialized, since only small bees performed effective visits. Flowers of R. neves-armondii may represent a case of cryptic floral specialization in which attributes other than morphology act as filters, restricting them to a single functional group of pollinators. Moreover, the four most frequent species of pollinators cover a spectrum ranging from solitary oligolectic to social polylectic bees, including an exotic species. These results illustrate the distinct dimensions of specialization-generalization that may occur in the pollination process of a single species.

摘要 植物与传粉者的互作谱系覆盖从专性特化类群到兼性泛化类群的完整范围，且花部形态与传粉系统未必完全匹配。本研究针对仙人掌族（Rhipsalideae）某物种的花部生物学、生殖系统及花部访客展开调查，核心聚焦传粉系统与花部表型之间的一致性。内叶丝苇（Rhipsalis neves-armondii）因自交不亲和属于专性异交物种，其花朵呈白色、体积小巧且昼间开放，辐射对称；结合少量花蜜的特征，该类花朵可被归类为表型泛化类群。本研究观测到的最常见传粉者包括1种独居寡食性地蜂科（Andrenidae）物种（Rhophitulus solani）、2种麦蜂亚科（Meliponinae）物种（旋刺无刺蜂Trigona spinipes与布氏无刺蜂T. braueri）以及西方蜜蜂（Apis mellifera）。尽管该物种具有泛化的花部表型，但其传粉系统实则为功能特化——仅小型蜂类可实现有效访花。内叶丝苇的花朵或代表一类隐蔽的花部特化案例：除形态外的其他性状可作为筛选过滤机制，将传粉者限制在单一功能类群中。此外，4种最常见的传粉者涵盖了从独居寡食性到群居多食性蜂类的完整谱系，其中还包括1种外来物种。本研究结果揭示了单一物种传粉过程中可能存在的特化-泛化多维格局。