Summer romance is in the air on the shortgrass prairie of southeastern Colorado. Quite literally, the alluring fragrance of Harrington’s evening primrose (Oenothera harringtonii) wafts in the breeze when the plant blooms each evening. Insects from bees to moths follow the scent to the flower of their dreams.
The insect’s choice of flower is significant to the future of the plant species, according to Krissa Skogen, Ph.D., Chicago Botanic Garden conservation scientist. After a pollinator lands on a plant and sips its nectar, it may carry a copy of a plant’s genes, in the form of pollen, to the next plant it visits. That next plant may then take those genes to combine with its own to form a seed—creating the next generation of Harrington’s evening primroses.
How do pollinators select a flower? According to Dr. Skogen, floral scent heavily influences their choices in addition to floral color and size. “Floral scent is this fascinating black box of data that a lot of reproductive biologists haven’t yet collected,” she said.
After studying the many pollinators of the evening primrose, from bees to moths, she found that two species of moths called hawkmoths—or more specifically, the white-lined sphinx moth (Hyles lineata) and the five-spotted hawkmoth (Manduca quinquemaculata)—are most effective. She told me that 30 percent more seeds are produced when a hawkmoth pollinates a plant rather than a bee.
“What’s really awesome about this system is that these hawkmoths can fly up to 20 miles in a night, while bees typically forage within one to five miles,” she added.
An insect so large it is often confused for a hummingbird, the brown-and-white hawk moths can carry genes between the widely spaced evening primrose populations.
In fact, Skogen has genetic data that support this idea—the roughly 25 populations she and her colleagues have studied throughout southeastern Colorado really act as two to three genetically, because the hawkmoths do such a great job moving pollen over long distances.
Making Sense of Scent
How do the hawkmoths use floral scent to decide which flower to visit? According to Skogen, they detect scent at a distance in the air with their antennae as they fly. (Once they get closer, flower color and size become more important in locating individual flowers.)
Skogen and her colleagues have determined that flowers in some populations smell very different from each other, and these differences in fragrance can be detected by humans. Fragrance combinations include green apple, coconut, jasmine, and even Froot Loops™.
Skogen’s theories suggest that differences in floral scent may direct female white-lined sphinx moths to the best host plants for their eggs, attract enemies (including seed-eating moths), reflect differences in soil, or the floral fragrance of other plant species flowering nearby.
What combinations of genes create the scents that best attract the hawkmoths? What do the genetic data of existing plants tell us about the direction genes have moved in the past? Are other insects, such as herbivores and seed predators, helping to move pollen or inhibiting reproduction?
These are the questions Skogen and her research team, including the Garden’s Jeremie Fant, Ph.D., and students Wes Glisson and Matt Rhodes, will investigate further. Late this summer and in future fieldwork, they will monitor the pollinators and collect floral and plant-tissue samples.
Back in the Harris Family Foundation Plant Genetics Laboratory and the Reproductive Biology Laboratory at the Garden, they will compare the genetic data of these plants with the observed patterns of the pollinators, and other floral data.
Each trip is another step closer to having a positive impact on the future of the state-imperiled evening primrose and its choice pollinators. This species is endemic, growing only in southeastern Colorado and northern New Mexico where the unique soils best suit its needs.
Because the species grows in limited locations and is easily thwarted by the impacts of development, climate change, invasive weed species, and other intensifying threats, it’s especially important that its future generations are strong.
Skogen’s love for nature has been lifelong. As a child in Fargo, North Dakota, she enjoyed playing in unplowed prairies. Now, at the Garden, she visits Dixon Prairie as often as she can. “There is beauty in the natural distribution of species,” she said. “The prairie habitat is imprinted on me from those childhood experiences. It feels like home.”
©2013 Chicago Botanic Garden and my.chicagobotanic.org