Premise: Animal pollinators play an important role in pollen dispersal. Differences in foraging patterns, flight distances and grooming behaviors are assumed to have consequences for genetic diversity of plants but are rarely tested explicitly. Here, we assess the role of pollinator functional groups with different foraging behaviors (hawkmoth and bee) in generating patterns of genetic diversity over similar geographic ranges for two closely related taxa.

Methods: This study focuses on two members of Oenothera section Calylophus that co-occur on gypsum outcrops throughout the Chihuahua Desert but differ in floral phenotype and primary pollinator: Oenothera gayleana (bee) and O. hartwegii subsp. filifolia (hawkmoth). We measured breeding system and floral traits in the greenhouse and conducted a population genetic study at the local (<13km; four populations) and landscape (60–440km; five populations) scales using 10–11 nuclear (pollen dispersal) and three plastid (seed dispersal) microsatellite markers. 

Key Results: Both taxa were self-incompatible and floral traits were consistent with expectations for different pollinators. We found no evidence of genetic structure at the local scale, but at the landscape scale, O. gayleana showed greater differentiation and significant isolation by distance than O. hartwegii subsp. filifolia. The plastid data were consistent with gravity dispersal of seeds and suggest that pollen dispersal is the principal driver of genetic structure in both species.

Conclusions: We demonstrate that pollinator functional groups can impact genetic differentiation in different and predictable ways. Hawkmoths, with larger foraging distances, can maintain gene flow across greater spatial scales than bees.

Floral morphology and leaf tissue for genetic samples were collected in wild populations in New Mexico and Texas, USA.

Floral morphology data and the breeding system assessment were conducted on plants grown in a growth chamber at the Chicago Botanic Garden, Illinois, USA.

Additional details of methods used can be found in the published manuscript (to be updated upon publication).