2012 Annual Report
1a.Objectives (from AD-416):
Objective 1: Using an insect-pollinated crop system, elucidate principles and data requirements for better predictions of gene flow via pollen in insect-pollinated crops.
Objective 2: Using squash with transgenic resistance to viral pathogens as a model system, develop a methodology to assess the impact of this transgene recently introduced into the genome of a wild species.
1b.Approach (from AD-416):
The number, types and acreages planted to transgenic crops are increasing. Consequently, there is a need to predict the likelihood of gene escape for different crops and a need to develop methodology to determine the impact of a transgene as it introgresses into wild populations. Because many crops benefit from insect pollination, part of our research investigates how distinct insect pollinators disperse pollen from plant to plant and ultimately among populations (gene flow). A better understanding of the impact of pollinator type on pollen dispersal would help us evaluate the differential risk of gene escape for distinct insect-pollinated crops while increasing our ability to select alternative pollinators for specific crops in the event of a major honeybee decline. On the one hand we study the impact of pollinator group on pollen dispersal and gene flow using the blue columbine as a model system. Information developed using this system will later be applied to different crops. On the other hand we examine the consequences of a disease resistance transgene that confers resistance to three economically important squash viruses as it introgresses into wild populations. We determine both the direct effects of the transgene on the fitness of free-living Cucurbita pepo (wild squash) and the indirect effects on diabroticite beetles (the primary non-target herbivore) and bacterial wilt (the major disease that these beetles transmit). In addition we measure gene flow among wild squash populations and gather basic information on their pollination biology and mating system. These types of data are critical to the efficient evaluation by regulatory agencies of the potential risk of transgenes introduced into wild plant populations.
We have started applying to alfalfa the knowledge on gene flow by insect pollinators gained from the model system, Aquilegia coerulea or the Rocky Mountain columbine. We have found, for both the Rocky Mountain columbine and alfalfa, that distinct insect pollinators have different probabilities of moving pollen long distance. We have also determined that characteristics of the landscape affect gene movement differently for distinct pollinators. Our data suggest that both pollinator type and landscape characteristics should be considered when examining gene flow by insect pollinators in agricultural systems. We are starting to link pollinator movement to gene flow and to determine if the distance moved between flower clusters, the direction of movement between flower clusters and the number of flowers visited per cluster are affected by the type of pollinators and by landscape characteristics.
We gathered this information for three pollinator types, honey bees, leaf cutter bees, and bumble bees. This field season we have started gathering data on the impact of patch size on pollinator movements for these three distinct pollinators. We have also started analyzing previous year data to highlight the major variables that affect pollinator movement for each pollinator type foraging within patches of alfalfa. This latter information is crucial to the development of a model of gene flow by insect pollinators.
Behavior of insect pollinators foraging on alfalfa. With the increasing acreages planted to transgenic crops and the increasing number of transgenes inserted into some crops, it is important to develop methodology to predict and try to minimize gene flow or the movement of genes from such crops. A first step in that direction is to understand the variables that affect pollinator movements as they forage in patches of flowers. ARS researchers and collaborators obtained and analyzed data on distances and directions traveled between flower clusters, and number of flowers visited per cluster and highlighted the variables that affected the behavior of pollinators foraging in patches of alfalfa flowers. For example, the more flowers visited in a cluster, the shorter the distance traveled to the next cluster. In insect-pollinated crops, knowledge and understanding of characteristics that affect pollinator behavior will help better predict and minimize gene flow by these pollinators. This information will ultimately benefit farmers, the general public and regulatory agencies interested in scientific data on the risk of gene escape from GE crops.
Soza, V., Brunet, J., Distilio, V., Liston, A. 2012. Phylogenetic insights into the correlates of dioecy in meadow-rues (Thalictrum, Ranunculaceae). Molecular Phylogenetics and Evolution. 63:180-192.
Brunet, J., Larson-Rabin, Z., Stewart, C.M. 2012. The distribution of genetic diversity within and among populations of the Rocky Mountain columbine: the impact of gene flow, pollinators and mating system. International Journal of Plant Science. 173(5):484-494.
Brunet, J., Larson-Rabin, Z. 2012. The response of flowering time to global warming in a high-altitude plant: the impact of genetics and the environment. Botany. 90(4):319-326.