In diverse flowering communities, a pollinator’s ability to distinguish between different plant species has direct consequences for plant fitness: heterospecific pollen transfer represents a cost to male fitness, and its presence on stigmas may interfere with subsequent pollination. Co-flowering plants may thus pay a cost for being perceived as similar by shared pollinators; to date, most work on this topic considers a single aspect of floral similarity. We investigated the reproductive biology of two species that share multiple aspects of phenotype. Dodecatheon alpinum (alt. Primula tetrandra) and Pedicularis groenlandica share similar color, rewards, behavioral requirements (buzz pollination), habitat preference. They flower concurrently, and are both predominately visited by Bombus (bumblebee) species. To understand if an overlap in multiple floral traits provides a benefit or cost to individual plants, we investigate pollen fates of D. alpinum and P. groenlandica moved by Bombus pollinators at two field locations in the Sierra Nevada. Populations were chosen where both species co-occur, and where they are isolated. Bees were observed foraging, and pollen samples were collected from foraging bees and identified using light microscopy. Stigmas were collected from both plant species and analyzed for pollen deposition.
Results/Conclusions
We first show that individual bumblebees move between D. alpinum and P. groenlandica within a foraging bout with detailed observation data. Switching between plant species varied by individual, with some bees switching frequently, and some showing floral constancy. We further show that pollen from both species is placed by plants on the bodies of foraging bees (n=84), with some evidence for spatial partitioning of pollen on bees’ bodies. Microscopic analysis of pollen samples indicate most bees sampled had pollen from multiple plant species, with pollen representing 27 plant species observed throughout the study. Corbicula samples collected from bees also contained multiple species of pollen, but varied by site in percent composition by D. alpinum, P. groenlandica, or other plant species. We further investigate how bee behavioral patterns translate to pollen deposition on plant reproductive tissues by analysis of 40 stigmas collected from populations where plants are interspersed, and where they occur in discrete patches. As a whole, these data illuminate the extent to which these species are co-pollinated, and will set the groundwork for further understanding patterns of convergence and divergence in complex multi-trait floral displays.