From a bee's eye:Effects of UV bullseye size on reproductive success in a dioecious vine Herpetospermum pedunculosum(Cucurbitaceae)

Descriptions of floral traits based on the visual capabilities of pollinators would advance our understanding of flower evolution and plantepollinator relationships.One such trait is the contrasting UV bullseye color pattern,which is invisible to human eyes but can be perceived by bee pollinators.However,it remains largely unknown how UV bullseye size affects male and female reproductive fitness.We examined UV bullseye patterns in the dioecious Herpetospermum pedunculosum,and quantified the effects of UV bullseye size on male and female fitness.Both UV bullseye size and flower size were larger in male flowers than in female flowers.The dominant pollinators of H.pedunculosum were bees,which could perceive the UV bullseye pattern.Bee pollinators exhibited a preference for male flowers with nectar rewards,and visited a greater number of male flowers on plants with a larger UV bullseye.Male reproductive fitness was found to decrease in plants with larger UV bullseyes,likely due to the high rate of intra-plant pollen transfer.Rewardless female flowers were less attractive to bee pollinators,resulting in pollen limitation of seed production.Female flowers with moderate UV bullseye size produced more seeds.Our results suggest that UV bullseye is subject to different selection via male and female fitness of H.pedunculosum with deceptive pollination,and large UV bullseye is generally not favored.This research is the first to examine the relationship between UV bullseye size and plant reproductive success,highlighting that floral evolution should be investigated from the pollinator's eye in future research.

The function of floral orientation in bluebells:interactions with pollinators and rain in two species of Mertensia(Boraginaceae)

Aims Pollinators are traditionally considered to be the primary agent of selection on floral traits.However,floral traits may also be under selection from abiotic agents(e.g.rain),which makes considering the relative importance of pollinators and abiotic selective agents on floral traits essential.The functional significance of floral orien-tation is often ascribed to pollinator attraction,but orientation can also protect reproductive structures from rain.Therefore,a study that incorporates both factors will enhance our understanding of the ecological roles of floral orientation in plant fitness.Mertensia brevistyla and M.fusiformis are herbaceous species that differ in their floral orientations.A series of field and laboratory experi-ments was used to investigate the adaptive function of floral orien-tation in these species,particularly with respect to pollinators and rain.Methods We measured and compared floral orientation and visitor assem-blages between M.brevistyla and M.fusiformis populations in west-ern Colorado,USA.We manipulated floral stems and conducted a choice experiment with floral visitors,and also compared orienta-tions of pollinator-visited stems with those of unvisited stems in a natural setting.We examined pollinator-and rain-mediated selec-tion on floral orientation by manipulating orientation,conducting supplemental pollinations,applying watering treatments and meas-uring subsequent seed set.We also experimentally tested the like-lihood of rain contact with anthers,and the effect of rainwater on pollen germinability.Important Findings Mertensia brevistyla had a significantly more upright floral orienta-tion than M.fusiformis,and seed set was highest in upright M.bre-vistyla and in horizontal/pendant M.fusiformis stems,supporting an adaptive function(via female fitness)of the interspecific difference in orientation.However,floral visitor assemblages did not differ significantly between the two species;visitors did not exhibit sig-nificant preference for either orientation;and pollinator-mediated selection on orientation was undetectable.Similarly,there was lit-tle effect of water on seed set in either species,regardless of floral orientation.However,pollen germinability was reduced in both species by immersion in water;and water was more likely to contact anthers in M.fusiformis than in M.brevistyla,due to interspecific differences in floral morphology.We conclude that pollinators are likely not the primary selective agent driving differences in orienta-tion in these Mertensia species.Instead,the negative effect of rain on pollen germinability helps explain the more pendant orientation of M.fusiformis,while short anthers in more upright M.brevistyla provide an alternative adaptation to rain.The selective agent driving effects of orientation on seed set remains unclear.This study illus-trates the necessity of considering male fitness and abiotic agents in interpreting the functional significance of inflorescence traits.