The stunning morphological diversity of Aquilegia flowers has been driven by rapid pollinator shifts: the bee pollination syndrome is ancestral, and there have been multiple independent transitions from bee to hummingbird, and hummingbird to hawkmoth syndromes (Whittall & Hodges 2007). The bee pollination syndrome is characterized by blue-purple flowers with short, curved nectar spurs; hummingbird-pollinated species are red with long, straight spurs; and the flowers of hawk moth-pollinated species have even longer spurs with white or yellow coloration. Many other traits such as pistil length, sepal size, nectar concentration and volume, inflorescence height, and petal blade area vary between pollination syndromes. To characterize the genetic architecture of these traits, we are conducting a QTL mapping experiment on F2 hybrids of bee- and hummingbird-pollinated parents, Aquilegia brevistyla & Aquilegia canadensis (pictured).
Of particular interest to the Kramer Lab is the evolution of petal morphology during these pollinator transitions. We have made progress characterizing the development of the straight spurs found in hummingbird- and hawk moth-pollinated species, and work on that front is ongoing (link to petal development page). We know next to nothing, however, about the development of the curved nectar spurs found in bee-pollinated species. What cellular processes are responsible for creating curvature in the spur, and how do they differ from those in straight spurs? Given that the bee syndrome is the ancestral state, we can also ask whether the same developmental strategy is deployed across bee-pollinated species to generate spur curvature. We have begun to answer these questions using our QTL data, and are also employing a comparative developmental approach as well as RNA-seq on parental petals to inform our search for causative loci.