The arctic vascular plant flora has traditionally been viewed as depauperate and is often considered to rely almost exclusively on asexual reproduction or wind-pollination, and thus advertisement for pollinators is viewed as unimportant or vestigial. While pollinators are generally accepted as the primary selective force on floral traits in temperate regions, their importance in shaping floral traits in the Arctic is poorly understood. To study pollinator-mediated selection in the Arctic, we focus on Parrya nudicaulis (Brassicaceae), a phenotypically variable species with individuals ranging from pure white-flowered to dark purple. Flowers were grouped into three stratified levels: white, light purple, and dark purple, with mean seed set per fruit used to estimate female reproductive fitness. Manipulations to flowers (pollen augmentation and pollen exclusion) were used to determine pollinator selective pressure on morphology and color variation relative to open-pollinated flowers.
Results/Conclusions
We found that P. nudicaulis had extremely low seed set in the absence of pollinators. We also detected pollen limitation, with seed set significantly increased in pollen augmentation over the open pollination treatment. All flower colors had equal reproductive success with pollen augmentation, but female reproductive success in light flowers was twice that of dark and white flowers when exposed to pollinators. Last, we detected significant directional phenotypic selection coefficients for petal width, corolla depth, and flower number of open pollinated plants. Contrary to previous beliefs on the lack of importance of pollinators on arctic plant reproduction, these results suggest arctic pollinators are indeed important for reproductive success in P. nudicaulis, and arctic pollinators also impose selective pressures on flower color and other floral traits.