Pollinator visitation, pollen deposition, and seed set for O. fruticosa

Heterospecific pollen transfer, the transfer of pollen between species, is
common among co-flowering plants, yet the amount of pollen received is
extremely variable among species. Intraspecific variation in
heterospecific pollen receipt can be even greater, but we lack an
understanding of its causes and fitness consequences in wild populations.
We examined potential drivers of variation in heterospecific pollen
receipt in Oenothera fruticosa. We evaluated the relationship between
heterospecific and conspecific pollen receipt and considered how
visitation by different pollinator groups, local floral neighborhood
composition, and flowering phenology affect the total amount and
proportion of heterospecific pollen received. Finally, we tested whether
variation in heterospecific pollen receipt translated into lower seed
production. Heterospecific pollen is ubiquitous on O. fruticosa stigmas,
but the amount received is highly variable and unrelated to conspecific
pollen receipt. Heterospecific pollen receipt depends on pollinator type,
the proportion of nearby conspecific flowers, and flowering date.
Significant interactions reveal that the effects of pollinator type and
neighborhood are not independent, further contributing to variation in
heterospecific pollen. Naturally occurring levels of heterospecific pollen
were sufficient to negatively impact seed set, but large amounts of
conspecific pollen counteracted this detrimental effect. Although
selection could act on floral traits that attract quality pollinators and
promote synchronous flowering in O. fruticosa, the risk of heterospecific
pollen is equally dependent on local floral context. This work highlights
how extrinsic and intrinsic factors contribute to intraspecific variation
in heterospecific pollen receipt in wild plants, with significant fitness
consequences.