Floral sex allocation inCorydalis ambiguapopulations visited by different pollinators

:We studied variations in reproductive success, pollinator behaviour, and intra-inflorescence sex allocation of Corydalis ambigua between populations having different pollinator types. This species is self-incompatible and predominantly pollinated by bumblebees. Bombus hypocrita subsp. sapporoensis was a dominant flower visitor in lowland populations. It behaved as a nectar robber but contributed as a pollinator. A legitimate pollinator, Bombus hypnorum subsp. koropokkrus, was common in mountainous areas. Seed production in lowland populations was intensively restricted by pollen limitation caused by low pollination efficiency of robber-like pollinators, whereas the extent of pollen limitation was small in mountain populations. Seed-set success under natural pollination significantly decreased in upper flowers within inflorescences in every population. Pistil mass, ovule number, and corolla mass decreased from bottom to top flowers in every population, corresponding to the seed-set pattern. Stamen mass and pollen number were almost identical among flower positions in lowland populations, whereas they increased from bottom to top flowers in mountain populations. Legitimate pollinators showed larger pollen removal per visit and tended to visit more flowers during a single stay than robber-like pollinators, resulting in more geitonogamous pollen flow (i.e., self pollination between flowers). When geitonogamy is intense, higher allocation to male function in upper flowers should increase donation success because bumblebees tend to leave an inflorescence from upper flowers. These results suggest that pollinator behaviour is a strong selective force causing variations in the sex allocation of plants.