New insights into the functional morphology of the lever mechanism of Salvia pratensis (Lamiaceae).
OBJECTIVE
The functional morphology of Salvia pratensis flowers was re-investigated, after new insights revealed that pollen dispensing is one of the main functions of the staminal lever. In particular, no detailed information was available regarding the process of pollen transfer and the forces arising between the pollen-bearing thecae and the pollinating bee's body. The assumption was made that these forces play a significant role in pollen dispensing.


METHODS
The functional morphology of S. pratensis flowers and the interaction between flowers and bees (Apis mellifera) were studied by reconstructing stress and strains by using qualitative and semi-quantitative theoretical analysis. Flowers were manipulated to study the spatial arrangement of the filament and lever, and of the head and proboscis of the visiting bee inside the tube. Photographs and films of bee visits on flowers were used to analyse the interaction of pollinator and staminal lever.


RESULTS
The spoon-shaped lower lever of S. pratensis has a small hole through which a bee introduces its proboscis into the corolla tube. Although mentioned for the first time by Kerner von Marilaun in 1891, presented here is the first drawing and the first photograph showing this interaction in detail. The analysis of the interaction of flower visitor and the lever mechanism revealed that the position of bees on different flowers is spatially very similar. Flower morphology constrains postures of legitimately nectar-probing bees within narrow bounds. A theoretical discussion on structural elements and force progression in the flower allows the principles of lightweight architecture in flower morphology to be recognized.


CONCLUSIONS
The staminal lever of S. pratensis is a pollen-dispensing device. It seems to influence the amount of pollen deposited on pollinators by determining the forces arising between the pollinator and the pollen. The relevant forces occur either during the first, dynamic phase or during the second, almost static phase of a flower visit.
Reith
Martin
M
Plant Biomechanics Group, Botanischer Garten, Universität Freiburg, Germany. salvia@gmx.de
Baumann
Gisela
G
Classen-Bockhoff
Regine
R
Speck
Thomas
T
D000818:Animals; D001516:Bees / Q000502:physiology*; D001696:Biomechanical Phenomena; D005247:Feeding Behavior / Q000502:physiology*; D035264:Flowers / Q000033:anatomy & histology / Q000502:physiology*; D027544:Salvia / Q000033:anatomy & histology / Q000502:physiology*