Effect of pollinator size on seed set in Lamium album var. barbatum

Background and aims – Previous researchers have demonstrated that geographic variation in pollinator community composition can generate diversity in the floral traits of animal-pollinated plants. Our study focused on the bumblebee-pollinated white dead-nettle Lamium album var. barbatum. Geographic variation in corolla length of this species is known to be correlated with regional pollinator size. The aim of this study is to clarify whether size-matching between flower and pollinator affects seed set in L. album.Material and methods – In the present study, we investigated two L. album populations on Mount Norikura, central Japan. We determined the pollinator community composition and corolla length during the flowering period of L. album and recorded seed set after a single visit by different pollinator categories.Key results – We observed that the main pollinators of L. album were bumblebee queens and workers. Bumblebee queens visited flowers more frequently than workers during peak flowering. Furthermore, size-matching between flowers and bumblebee queens, but not workers, strongly promoted seed set. These results suggest that L. album flower size is adapted to bumblebee queens, the main pollinator during peak flowering season in our study sites.