Fine-tuned floral filters in melittophilous flowers sort out particular bees
Sensory and Behavioural Biology
Final Report Abstract
Bees are considered reliable pollinators, because they are frequent and constant flower visitors. But since bees also collect large amounts of pollen for larval food provisioning and pollen grains which have been groomed into the pollen transport structures are no longer available for pollination, beepollinated flowering plants face a pollen dilemma: Plants that use bees as pollen vectors have to deposit pollen grains on the bees’ body, but have to assure that the deposited pollen is not collected or at least not entirely collected by the bees. In studies on pollination networks, a flower visit by a bee is often equated a pollination event. Here we question this equation and ask if and how bee-pollinated flowering plants benefit from fine-tuned floral filters to exclude particular bees. The hypothesis that corbiculate bees are unable to collect pollen of most Malvoideae was successfully tested in a flight cage experiment. Some aspects helping to prevent pollen collection in the pollen baskets of corbiculate bees such as pollen grain size and spine length were found. However, pollenkitt composition, which has hardly been studied so far, may be the key to definitively solving this puzzle. The pollen collection behaviour of megachilid bees possessing a ventral scopa was investigated using pollen grains marked by quantum dots. The effectiveness of the ventral scopa to collect and store pollen while picking up pollen grains by tapping the pollen-presenting florets is high and suggests that the bees mainly transfer self-pollen. The heterantherous buzz-pollinated Rhynchanthera grandiflora was studied in Brazil. The hypothesis of division of labour between inconspicuous pollination stamens and conspicuous feeding stamens thought to attract and manipulate suitable pollinators does not apply in this case where pollen grains of both types of stamens are specifically deposited on the bees’ body. Upon sonication, the short stamens deposit pollen on the ventral side of the bees, while the long stamen focusses and directs the pollen jet to deposit pollen grains specifically on the back of the bees. Altogether, our basic hypothesis of fine-tuned floral filters in melittophilous flowers excluding particular bees with probably lower pollination efficiency was confirmed and enriched with many details about its mechanisms.
Publications
- (2019) Pollen grain morphology is not exclusively responsible for pollen collectability in bumble bees. Scientific Reports 9: 4705
Konzmann S, Koethe S, Lunau K
(See online at https://doi.org/10.1038/s41598-019-41262-6) - (2019) Pollinator effectiveness of a specialist bee exploiting a generalist plant – tracking pollen transfer by Heriades truncorum with quantum dots. Apidologie
Konzmann S, Kluth M, Karadana D, Lunau K
(See online at https://doi.org/10.1007/s13592-019-00700-0) - (2020) Morphological specialisation of heterantherous Rhynchanthera grandiflora (Melastomataceae) accommodates pollinator diversity. Plant Biology
Konzmann S, Hilgendorf F, Niester C, Rech AR, Lunau K
(See online at https://doi.org/10.1111/plb.13102)
