Elevational Floral Size Variation in Prunella vulgaris

Floral size is potentially influenced by local pollinators’ body size. As pollinator fauna and size often change with elevation, correlation between elevational variation of pollinator size and floral size is expected. We investigated the variation of floral size in Prunella vulgaris L. (Laminaceae) and the variation of their pollinator fauna along an elevational gradient. We measured the floral size of four traits: corolla length (CL), corolla tube length (CTL), corolla width (CW), and calyx length (CAL), in 23 populations, and found that CL and CTL were negatively correlated with elevation, and CW and CAL were not. Six bumblebee species visited the flower, and the visiting bee fauna differed among populations; the smallest and the largest bumblebee species visited the high elevational range (above 1800 m a. s. l.) populations, and the largest and the second largest bumblebee species visited the middle elevational range (1400 - 1800 m a. s. l.). Although abiotic factors can potentially affect floral size, the fact that we do not find an elevational decrease in CW and CAL suggests that the elevational change in P. vulgaris’s CL and CTL reflects the local pollinator size.