Plant–pollinator interactions vary along a specialization–generalization continuum. Advances in understanding the evolutionary and ecological consequences of different degrees of specialization depend on precise data on plant–pollinator interdependency. We studied the association of Parodia neohorstii (Cactaceae) and its bee pollinators focusing on pollinator foraging behaviour, flower functioning, female and male reproductive success, and pollen fate. Parodia neohorstii showed synchronized flower opening and pollen presentation but discontinuous blooming. The apparently generalized flowers partition pollen through thigmonastic stamen movements that function as a mechanical filter against generalist bees by restricting access to the major pollen reservoir to bees that show flower handling ‘know-how’, thereby favouring the oligolectic bee Arhysosage cactorum. This pollinator adjusted its pollen foraging to flower opening, removed pollen hurriedly, and promoted maximal fruit and seed set, which was minimal in its absence. Estimates of pollen fate revealed that a huge amount of pollen flows to specialized pollinators (86.5%), and only 0.9% reaches conspecific stigmas. The specialized interaction between P. neohorstii and Arhysosage cactorum, both threatened species, is efficient but fragile. Any environmental modification that causes a mismatch between the partners is likely to result in reproductive failure.
Analyses of resource presentation, floral morphology and pollinator behaviour are essential for understanding specialised plant‐pollinator systems. We investigated whether foraging by individual bee pollinators fits the floral morphology and functioning of Blumenbachia insignis, whose flowers are characterised by a nectar scale‐staminode complex and pollen release by thigmonastic stamen movements.
We described pollen and nectar presentation, analysed the breeding system and the foraging strategy of bee pollinators. We determined the nectar production pattern and documented variations in the longevity of floral phases and stigmatic pollen loads of pollinator‐visited and unvisited flowers.
Bicolletes indigoticus (Colletidae) was the sole pollinator with females revisiting flowers in staminate and pistillate phases at short intervals, guaranteeing cross‐pollen flow. Nectar stored in the nectar scale‐staminode complex had a high sugar concentration and was produced continuously in minute amounts (~0.09 μl·h−1). Pushing the scales outward, bees took up nectar, triggering stamen movements and accelerating pollen presentation. Experimental simulation of this nectar uptake increased the number of moved stamens per hour by a factor of four. Flowers visited by pollinators received six‐fold more pollen on the stigma than unvisited flowers, had shortened staminate and pistillate phases and increased fruit and seed set.
Flower handling and foraging by Bicolletes indigoticus were consonant with the complex flower morphology and functioning of Blumenbachia insignis. Continuous nectar production in minute quantities but at high sugar concentration influences the pollen foraging of the bees. Partitioning of resources lead to absolute flower fidelity and stereotyped foraging behaviour by the sole effective oligolectic bee pollinator.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.