Association of flower color with pollen reward may explain increased bumblebee visitation to the Scotch broom yellow morph

Given that pollinators usually visit flowers for hidden rewards, they need to rely on floral traits indicate reward status (“honest signals”). However, the relationship between pollination, honest signals, and rewards is little documented in natural conditions. The Scotch broom (Cytisus scoparius) an invasive shrub with polymorphism color of its can be yellow, orange, or red. In three areas dominated by broom, we described abundance morphs estimated bumblebee (Bombus terrestris) visitation rate. We examined whether was related pollen reward. collected classified their stamens according function: export. Then, measured anther size quantity. yellow morph more abundant visited bumblebees than orange red morphs. did indeed offer other this occurred only rewarding anthers, suggesting could use as signal most flowers. discuss innate and/or learned preferences explain why visited, pollinated, abundant, while are maintained at a lower frequency. This one few field works shows variation intra-specific associated pollinator rate, helping understand foraging coexistence nature. Clinical trials registration: Not applicable.