Richard Sands recently published a paper from his MPhil project, which shows that plant genetic background is an important factor in determining the number of bumblebees interacting with red-clover. Richard looked at the ability of a number of agricultural cultivars and wild populations of red clover (Trifolium pratense) to attract the common carder bee (Bombus pascuorum). Although the bees showed no specific preference for the cultivars or the wild populations of plants per se, they did discriminate among cultivars and among populations, favouring some over others. The bees seemed to prefer plants with either larger inflorescences and more pollen, or a greater number of inflorescences, and these plant traits were determined by the genetic background of the plants. This is an important finding as it shows that seed source needs to be carefully considered when choosing plants to attract pollinators.
Sands RJ, Rowntree JK (2016) Interactions between the Bumblebee Bombus pascuorum and Red Clover (Trifolium pratense) Are Mediated by Plant Genetic Background. PLoS ONE 11(8): e0161327. doi:10.1371/journal.pone.0161327
Wildflower mixes are often planted around field margins to provide forage for pollinators. Although seed for these mixtures is often wild-sourced, for species where agricultural cultivars are available, for example red clover (Trifolium pratense), cultivars can also be included. Previous evidence suggests that plant genetic background can have a strong influence on plant-arthropod interactions and therefore the provenance and genetic background of the plants included in wildflower mixes could impact plant-pollinator interactions. We tested the performance of five individual T. pratense cultivars against two commercially available wild-sourced T. pratense populations in terms of their ability to attract potential pollinator species (focusing on bumblebees) and their floral traits using greenhouse and garden experiments. The main bumblebee observed interacting with T. pratense was Bombus pascuorum and we found no difference in the absolute number of B. pascuorum visiting the cultivars or wild populations. However, we found variation among cultivars and between wild populations in their ability to attract bumblebees, which seems to be related to their relative investment in different floral traits. There was a positive relationship between biomass and number of inflorescences produced by the wild populations of T. pratense, which was not apparent for the cultivars. This suggests that artificial selection on the cultivars has changed the G-matrix of correlated traits. We show that agricultural cultivars of T. pratense can be as effective as wild populations at attracting pollinators such as bumblebees, but that the genetic background of both cultivars and wild populations can have a significant impact on the attractiveness of the plant to pollinators. We also show divergence in the correlated traits of T. pratense cultivars and wild populations that could lead to outbreeding depression if the plants interbreed.