Geographic changes in pollinator species composition affect the corolla tube length of self‐heal ( Prunella vulgaris L.): Evidence from three elevational gradients

Geographic difference in pollinator fauna and variation in average pollinator size may lead to local adaptations of flower size that enhance pollen transfer efficiency. Here, we show that flower size (corolla tube length) of Prunella vulgaris varies both laterally and along elevational gradients, in parallel with local pollinator proboscis length. We measured geographic variation in corolla tube length and leaf length of P. vulgaris , and in proboscis length of its bumblebee pollinators, in 12 populations on three different mountains. In estimating pollinator proboscis length, we considered both the average proboscis length of each bumblebee species and the species composition of bumblebees visiting P. vulgaris flowers. We then ascertained whether pollinator proboscis length, elevation itself, or resource availability (indicated by leaf length) correlated with corolla tube length. We found that the local pollinator species composition varied along elevation and among mountain areas, and this variation corresponded to geographic variation in the average pollinator proboscis length. Similarly, corolla tube length of P. vulgaris varied along elevation and among mountain areas. We found that the corolla tube length variation was not associated with elevation itself or local resource availability but was strongly associated with local pollinator average proboscis length. Although corolla tube length was generally shorter at higher elevation, it was relatively longer in some high‐elevation populations, where bumblebees having long proboscis length ( Bombus consobrinus and B. diversus ) visited the flowers. Therefore, parallel changes in P. vulgaris corolla tube length and pollinator proboscis length occur across a wide geographic region in central Japan.