Pollinator-Mediated Selection on Floral Traits in the Arctic Plant
Parrya nudicaulis (Brassicaceae)
Abstract
The evolution of floral traits is largely attributed to
pollinator-mediated selection; however, the importance of pollinators as
selective agents in pollen-limited environments is poorly resolved. In
pollen-limited arctic and subarctic regions, selection is expected to
either favor floral traits that increase pollinator attraction or
promote reproductive assurance through selfing. We quantified phenotypic
selection on floral traits in two arctic and two subarctic populations
of Parrya nudicaulis. Additionally, we measured selection in plants in
both open-pollination and pollen-augmentation treatments to estimate
selection imposed by pollinators in one population. Seed production was
found to be limited by pollen availability and strong directional
selection on flower number was observed. We did not detect consistently
greater magnitudes of selection on floral traits in the arctic relative
to the subarctic populations. Directional selection for more pigmented
flowers in one arctic population was observed however. In some
populations, selection on flower color was found to interact with other
traits. We did not detect consistently stronger selection gradients
across all traits for plants exposed to pollinator selection relative to
those in the pollen-augmentation treatment; however directional
selection tended to be higher for some floral traits in open-pollinated
plants.