Comparing the efficiency of pollination mechanisms in Papilionoideae

The pump pollination mechanism is typical of basal clades within Papilionoideae and might be associated with less efficient pollen transfer systems, while the explosive tripping mechanism is considered more advanced and might represent the highest expression of the trend in pollen economy. Crotalaria pumila, C. stipularia, Desmodium incanum and D. subsericeum present secondary pollen presentation with pump and explosive pollination mechanisms, respectively. In the present study, we evaluate and compare (1) pollen removal, (2) pollen deposition and (3) pollen transfer efficiency of both mechanisms, considering single visits by Megachile spp., common pollinators of the four plant species in Salta Province, Argentina. Comparisons of visit durations are made in relation to the type of mechanism and rewards offered. We detected significant differences between both mechanisms in the proportion of pollen grains removed and deposited in a flower after a single visit of Megachile. We found that efficiency in pollen transfer was significantly higher for explosive mechanism (2.13?±?0.42 pollen grains deposited per 100 removed) than for pump mechanism (0.33?±?0.17 pollen grains deposited per 100 removed). This is the first study that compares efficiency between pollination mechanisms in this group of plants.