Pollinator visitation closely tracks diurnal patterns in pollen release

PREMISE

Animal-pollinated plants face a high risk of pollen loss during its transfer. To limit the negative effect of pollen losses by pollen consumption and heterospecific transfer, plant species may adjust and stratify their pollen availability during the day (i.e., "schedule" their pollen presentation) and attract pollinators in specific time frames.

METHODS

We investigated diurnal patterns of pollen availability and pollinator visitation in three coflowering plant species: Succisa pratensis with open flowers and accessible pollen, pollinated mainly by pollen-feeding hoverflies; Centaurea jacea with open flowers and less accessible pollen, pollinated mainly by pollen-collecting bees; and Trifolium hybridum with closed flowers and pollen accessible only after the active opening of the flower, pollinated exclusively by bees.

RESULTS

The three plant species differed in the peak pollen availability, tracked by the visitation activity of their pollinators. Succisa pratensis released all pollen in the morning, while pollinator activity was still low and peaked with a slight delay. In contrast, C. jacea and T. hybridum had distinct pollen presentation schedules, peaking in the early afternoon. The pollinator visitation to both of these species closely matched their pollen availability.

CONCLUSIONS

Stratifying pollen availability to pollinators during the day may be one of several mechanisms that allow coflowering plants to share their pollinators and decrease the probability of heterospecific pollen transfer.

Genetic variations and in vitro root-colonizing ability for an ericaceous host in Sarcoleotia globosa (Geoglossomycetes)

We discovered that Sarcoleotia globosa (Geoglossomycetes) fruited on the soil of ornamental Erica pot cultures, and its ascospores can germinate on plain agar. These findings prompted us to collect isolates from horticultural and natural environments in Japan and analyze their phylogeny and root colonizing ability. Pure cultures were successfully obtained from ascospores and surface-sterilized ericaceous roots. Phylogenetic analysis based on rRNA internal transcribed spacer sequences revealed that Japanese samples were separated into three strongly supported clades. Individual clade consisted of samples derived from (1) Erica pot cultures, (2) Rhododendron planted in a garden or Vaccinium pot culture, and (3) natural habitats in Hokkaido. Colony characteristics and in vitro root-colonizing morphology observed may correspond to these phylogenetic variations. Irrespective of the clades, all tested strains formed hyphal coils in vital rhizodermal cells of V. virgatum seedlings, which resembled those of ericoid mycorrhizae. Our results represent novel findings that can be the first step in unraveling the currently unknown ecology of geoglossoid fungi.