Submitted to: Molecular Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/16/2009
Publication Date: 9/1/2009
Citation: Brunet, J., Holmquist, K.G. 2009. The Influence of Distinct Insect Pollinators on Female and Male Reproductive Success in the Rocky Mountain Columbine. Molecular Ecology. 18(17):3745-3758. Interpretive Summary: How an insect pollinator moves pollen around affects the risk of gene escape via pollen. A pollinator that visits nearest neighbor plants may limit gene flow relative to a pollinator that typically flies long distances between plants. While one may anticipate that distinct pollinators differentially affect pollen movement, there exists little direct evidence to confirm such predictions. Understanding why and how different insect pollinators affect gene flow will help better predict the risk of gene escape for different crops. Such knowledge is important to farmers, seed industries and regulatory agencies. In this study we compared how two distinct insect pollinators moved genes via pollen in a population of our model system, the rocky mountain columbine, Aquilegia coerulea. Hawkmoths and bumble bees are the two major pollinators of the rocky mountain columbine. Bumble bees collect pollen throughout the day and frequently groom; hawkmoths do not groom, collect nectar at dusk and in the process pick up pollen. Because these pollinators have such strong differences in behavior we expected that if any differences existed between pollinator types they would be expressed in this system. We used genetic markers named microsatellites to determine paternity of seeds within a population for plants visited by either bumble bees or hawkmoths. We bagged plants during the day and unbagged them in the evening for hawkmoth visited plants and did the opposite treatment for bumble bee visited plants. Contrary to our expectations, bumble bees commonly moved pollen long distances (> 100 m). Both pollinator types had similar effects on number of recipients visited and genetic diversity of the progeny on these recipients. Pollen carried by each pollinator type sired the same number of outcrossed seeds. We found fewer differences than we had anticipated in how bumble bees and hawkmoths moved genes around within a population. Our data indicated that differences in number of visits for each pollinator together with differences in pollen carryover curves helped explain the similarity between the two pollinator types on their impact on gene flow. Thus to predict the impact of distinct insect pollinators on gene flow on the same crop we need to know not only how each pollinator moves pollen from flower to flower (pollen carryover curve) but also the total number of visits made to flowers by each pollinator type.
Technical Abstract: Different groups of pollinators with contrasting behavior may differentially affect gene dispersal and gene flow. Hawkmoths and bumble bees are the two major pollinators of the rocky mountain columbine, Aquilegia coerulea. Bumble bees collect pollen throughout the day and frequently groom; hawkmoths do not groom, collect nectar at dusk and in the process pick up pollen. In this study, we used microsatellite marker based paternity analysis to determine whether these two insect pollinators differentially influenced how genes are moved via pollen in a population of A. coerulea. We first tested whether bumblebees moved genes via pollen mostly within patches to nearest neighbor plants, while hawkmoths dispersed genes more evenly within and between patches of plants. Second, as a result of more rapidly decaying pollen dispersal curves due to grooming in bumble bees, we expected bumble bees to move pollen to fewer recipients and less evenly among recipients. We also expected bumble bees to carry less diverse pollen to the recipients. Finally, because hawkmoths are commonly associated with the evolution of A. coerulea flowers, we tested whether plants visited by hawkmoths had greater male reproductive success and sired more outcrossed seeds than plants visited by bumblebees. Bumble bees were stronger pollinators than we had anticipated. Bumble bees did not limit pollen movement to nearest neighbor plants but frequently moved successful pollen among patches separated by 150 meters. Pollen carried by bumble bees and hawkmoths reached the same number of recipients and recipients had similar progeny genetic diversity. In addition, pollen moved by bumble bees sired similar number of outcrossed seeds relative to pollen moved by hawkmoths. However, pollen moved by bumble bees sired more outcrossed seeds when moved shorter distances (within as opposed to between patches), a pattern not observed for hawkmoths. Overall bumble bees were as efficient pollinators as hawkmoths via male function and had a similar influence on progeny genetic diversity and thus both pollinator types are expected to have similar influence on floral evolution and the fine scale genetic structure of the population.