Animal pollinators exert selective pressure on plants they pollinate. Pollinator-mediated selection is typically associated with traits that increase the visibility, attractiveness and utility of flowers to their pollinators. Although Oncocyclusirises are large and showy, they do not produce a nectar reward. They are, however, completely self-incompatible and depend on night-sheltering Eucera bees for pollination. This night-sheltering system is putatively associated with a heat reward, which enables bees that sleep in iris tunnels to emerge earlier in the morning than their ground-nesting counterparts. In this study, we used artificial iris flowers in five size classes to ask (1) whether pollinators select on flower size in irises and (2) if so, do their choices among flowers of different sizes correspond with the potential heat reward?
Results/Conclusions
We found that pollinators prefer intermediate-sized flowers and that intermediate-sized flowers warm faster at sunrise than other flower sizes. These data suggest that pollinator preference for intermediate sized flowers may be associated with the heat reward offered by these dark-colored irises to night-sheltering bees. This work offers new avenues of research using artificial flowers in natural systems to disentangle the traits under pollinator-mediated selection, and specifically whether a preference for intermediate sized flowers, in this system, is a learned preference based on the heat reward.