Abiotic environmental changes along altitude influence plant distribution and character variation. The flower size variation may also be influenced by these abiotic factors. On the other hand, geographic variations of flower size have often been reported to reflect selection pressure by regional pollinator fauna.

Campanula punctata var. hondoensis is distributed over a broad altitudinal range, and their pollinator composition seems different along altitude. Thus, the selection pressure by pollinators may differ among altitudes.

Here, we investigate the pollinator composition, flower size variation and gene flow along altitudinal gradient and found that 1. the composition of Bombus pollinators changes along altitude, 2. the flowers are basically smaller in higher altitudes, 3. the flower size along altitudinal gradient correlates with pollinator size, 4. microsatellite analyses suggest no genetic differentiation along altitude.

These results suggest that flower size variation along altitude is influenced by the pollinators' selection pressure, and is maintained even in the presence of gene flow.