Archives For hawkmoth research

Imagine an episode of the Jerry Springer Show in which the paternity of a child will be determined. Now imagine that instead of human beings, the show is focused on plants, and the issue at hand is the paternity of seeds produced by a given flower.

Next, consider that instead of just two candidate dads, there are dozens or even hundreds of individuals that could have fathered those seeds. What would you expect to find out at the end of the episode?

New research by biologists at Chicago Botanic Garden and the University of Arizona brings such a scenario into reality, and the “big reveal,” while not quite as dramatic as what you’d typically see on the Springer show, offers new insights into plant mating. The paper, titled “Pollinator identity and spatial isolation influence multiple paternity in an annual plant,” was published online today in Molecular Ecology.

“Biologists have known for decades that multiple paternity is common in plants—that is, the seeds contained in a fruit will often have been fathered by many different individuals,” said Matt Rhodes, a Ph.D. student in ecology and evolutionary biology at the University of Arizona. “While we have long had a basic understanding of how multiple paternity occurs in plants, we wanted to explore how it might be influenced by some of the messier aspects of pollination ecology.”

Much of this messiness stems from the fact that plants are sessile: once they start growing, they’re stuck where they are. “One important consequence of this immobility is that plants can’t seek out mates on their own,” Rhodes explains. “Instead, most flowering plants entrust the mating process to animal pollinators that move pollen from flower to flower. On top of that, some individuals are surrounded by potential mates while others are spatially isolated. There are good reasons to expect both of those factors to influence multiple paternity, and that’s what motivated our study.”

In the video above, pollen is deposited on the proboscis and body as hawkmoths (Hyles lineata and Manduca quiquimaculata) visit flowers of Oenothera harringtonii. (Video: K. Skogen) View video on YouTube here.

To address these issues, Rhodes went to the grasslands of southeastern Colorado with Jeremie Fant and Krissa Skogen, conservation scientists at the Chicago Botanic Garden who co-authored the article. They studied a rare evening primrose species with a strange twist in its pollination ecology: its flowers are visited by large-bodied hawkmoths at night and comparably smaller-bodied bees during the morning. “Based on these differences in body size as well as some important differences in behavior, we predicted that flowers visited by hawkmoths would mate with a greater number of fathers than those visited by bees,” said Skogen. “Because these floral visitors are active at different times of day, we were able to test this prediction with a fairly simple experiment in which we limited different flowers on a plant to visits from either hawkmoths or bees. We also predicted that multiple paternity would be less likely for individuals that were farther away from potential mates.”

Hyles lineata visits an Oenothera harringtonii flower; note the pollen on the moth’s head and body. (Photo: S. Todd)

Hyles lineata visits an Oenothera harringtonii flower; note the pollen on the moth’s head and body.
(Photo: S. Todd)

A Lasioglossum bee collects pollen from the anthers of an Oenothera harringtonii flower without coming into contact with the stigma. (Photo: S. Todd)

A Lasioglossum bee collects pollen from the anthers of an Oenothera harringtonii flower without coming into contact with the stigma. (Photo: S. Todd)

After collecting the seeds from these plants, the researchers spent months examining seed DNA in the genetics lab. “By comparing the seeds’ DNA to the DNA of the maternal plants from which we collected them, we were able to figure out which parts of the DNA came from the father,” explains Fant. “We then screened that paternal DNA against all of the individuals in the population—which in our case included more than 300 plants spread across 2 square miles of the landscape—to find the most likely father for each of the seeds we collected.”

For the most part, the results were consistent with the researchers’ predictions. “We found that on average, flowers visited by hawkmoths mated with nearly twice as many different fathers as flowers visited by bees,” said Rhodes. “We also found that spatially isolated individuals were far less likely to mate with multiple different fathers. Overall, it looks as though plant ‘promiscuity’ depends both on what kind of animal visits the flowers, and how far away that individual is from potential mates.”

Scales from Hyles lineata were deposited on the stigma of an Oenothera harringtonii flower. (Photo: K. Skogen)

Scales from Hyles lineata were deposited on the stigma of an Oenothera harringtonii flower. (Photo: K. Skogen)

In addition to providing a more thorough account of factors that can influence multiple paternity in plants, the results also allow researchers to consider how plants might be affected by the loss of certain pollinators. “This study allows us to make predictions about how some plants may be affected if particular pollinators disappear. Hawkmoths play an important role in moving pollen from plant to plant; if they decline in large numbers or are lost completely, there may be cascading effects on the success of future generations of hawkmoth-pollinated plants” said Skogen.

Comanche National Grasslands, Colorado— the shortgrass prairie where the study was conducted. (Photo: K. Skogen)

Comanche National Grassland, Colorado— the shortgrass prairie where the study was conducted. (Photo: K. Skogen)

The field team in Colorado (left to right: Kelly Ksiazek, Matt Rhodes, Sadie Todd, Evan Hilpman, Krissa Skogen, and Jeremie Fant)

The field team in Colorado (left to right: Kelly Ksiazek, Matt Rhodes, Sadie Todd, Evan Hilpman, Krissa Skogen, and Jeremie Fant)


©2017 Chicago Botanic Garden and my.chicagobotanic.org

To most people, the word “pollinator” is synonymous with the word “bee,” but only a fraction of plants are pollinated by bees.

In fact, many different insects and mammals are pollinators—bats, birds, beetles, moths, and more. As part of National Moth Week, we wanted to highlight our work on a very special group of moths: the Sphingidae, or hawkmoths, which pollinate more than 106 plant species in North America alone, and many more around the world.

PHOTO: A newly emerged Hyles lineata hawkmoth.

A newly emerged Hyles lineata hawkmoth

I am a research tech in the Skogen lab. I work with Krissa Skogen, Ph.D., her postdocs Tania Jogesh and Rick Overson, and fellow Garden scientist Jeremie Fant, Ph.D., on a National Science Foundation Dimensions of Biodiversity project entitled, “Landscapes of Linalool: Scent-Mediated Diversification of Flowers and Moths across Western North America.” Our project looks at floral scent and pollination in the evening primrose (Onagraceae) family.

Many species in the evening primrose family are pollinated by the white-lined hawkmoth (Hyles lineata). This pollinator is also an important herbivore! Female moths lay eggs on evening primroses, and their hungry caterpillars feed on the leaves, buds, and flowers. How does scent play a role in attracting hawkmoths? Do moths use it for pollination? Or do they use it to find host plants to lay their eggs? Or maybe both?

PHOTO: Hawkmoth pupae (Hyles lineata).

Hawkmoth pupae (Hyles lineata)

PHOTO: Hyles lineata eggs on an Oenothera harringtonii plant.

Hyles lineata eggs on an Oenothera harringtonii plant

From Dr. Skogen’s prior research, we know that floral scent can vary within and between plant populations. For instance, within the species O. harringtonii, some populations produce a scent compound called linalool while others do not. We think that the plants face a signaling dilemma: How do they use floral scent to invite their pollinators and yet avoid getting eaten? If female moths use linalool to lay eggs, then perhaps, in some populations, the plants benefit from not advertising their scent. To test this idea, we needed to conduct behavioral experiments to understand how Hyles perceive floral scent

This summer, along with Victoria Luizzi, a summer REU student from Amherst College, we looked at which plants female moths prefer to lay their eggs on—plants from populations containing linalool, or plants from populations without linalool. To answer this question, we first went to Colorado (where the plants naturally grow) and got plants from two different populations, one population that we know produces linalool and another we know doesn’t. Meanwhile our collaborator, Rob Raguso at Cornell University, sent us hawkmoth pupae and we patiently waited for them to emerge.

PHOTO: Victoria Luizzi (left) and Andrea Gruver (right) dissect a female moth to count remaining eggs.

Victoria Luizzi (left) and Andrea Gruver (right) dissect a female moth to count remaining eggs.

When the moths emerged they were placed in mating cages. Once mating occurred, females were transferred to a quonset in the evening that contained four plants from the linalool population and four plants from the non-linalool population. The moths were left overnight so the females had plenty of time to choose where they wanted to lay their eggs. The next morning, Victoria counted the eggs on each plant (which was sometimes hundreds!) to see on which plants the females were choosing to lay their eggs. In addition, we dissected each moth to see how many eggs the female did not lay.

PHOTO: Krissa Skogen moves a moth to its new enclosure in her office.

Krissa Skogen moves a moth to its new enclosure in her office

Over the course of the project, 12 females were flown in the quonset. Overall, the moths showed a preference for plants from the population that produces linalool. These data suggest that plants risk inviting foes while advertising to their friends—but we’ll need to collect a lot more data to be certain. Ultimately, both the insects that pollinate flowers as well as the insects that eat them might determine how a flower smells! We hope to continue this study to test our hypothesis further and learn more about how scent influences hawkmoth behavior, and how hawkmoth behavior influences floral scent and other floral traits of the plants they pollinate.


©2016 Chicago Botanic Garden and my.chicagobotanic.org