Author: Krissa Skogen

Krissa Skogen, Ph.D., is a conservation scientist and manager of the Conservation and Land Management (CLM) Program at the Chicago Botanic Garden. Her research focuses on pollinator ecology, plant reproductive biology, and population-level studies to explain variation in neutral traits (molecular markers) and those under selection (floral attractants, rewards, etc.). Her current work focuses on an endemic evening primrose, Oenothera harringtonii, and other species pollinated by hawkmoths and bees. The CLM Program places between 80 and 100 interns with federal biologists in the western United States each year.

Hawkmoth Pollination Promotes Promiscuity in Plants

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.”

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)

Filming “Plants Are Cool, Too!”

This past spring I was asked by a friend and colleague, Chris Martine, to be featured in an upcoming episode of Plants Are Cool, Too!

A few months later, in August, we taped episode 4, focusing on my work with plants and pollinators, and episode 5, which will feature the work of Mike Moore of Oberlin College on gypsum-endemic plants (to be released later this year).

PHOTO: Chris Martine and cameramen filming against New Mexico scenery. — Chris Martine shoots the intro to *Plants Are Cool, Too!,* episode 4. (Photo: Krissa Skogen)

So what exactly is Plants Are Cool, Too!?

Chris Martine created the web-based series Plants Are Cool, Too! to address a gap in the nature show genre: there are no shows focused explicitly on plants that might engage people, from elementary school kids on up. He set out to create a series focusing on some of the coolest plants, their stories, and the scientists who study them. As of today, four episodes have been released:

Episode 1 — The Pale Pitcher Plant
Episode 2 — Fossilized Forests
Episode 3 — Undead Zombie Flowers of Skunk Cabbage
Episode 4 — Desert Plants and Marathon Moths (my show—see it at the end of this post!)

Adventures with botanists and filmmakers

So what does it take to create an episode? And how about two episodes at once, in just three days? Certainly, lots of planning, people who know the lay of the land, and a fantastic film crew. Thankfully, Chris is really good at what he does—the team of people he pulled together couldn’t have been better.

PHOTO: Hartweg's sundrops blooming at dusk. — The star of the show: Hartweg’s sundrops (*Oenothera hartwegii* spp. *filifolia*), a night-blooming member of the evening primrose family. (Photo: Krissa Skogen)

Our first site for filming was Yeso Hills, just southwest of Carlsbad, New Mexico. We arrived at the golden hour, when the sun is near the horizon and casts a golden light on everything. As we turned off the highway onto a gravel road, we encountered a sea of sundrops (Oenothera hartwegii and O. gayleana). I had a hard time containing my excitement. I’ve seen photos of populations like this, but nothing like it in person. There were plants everywhere, hundreds of them, their yellow flowers on full display, glowing magnificently in the setting sun. I suspected it would be a fantastic night for hawkmoths—how could they not be drawn to this fantastic population? So many plants, so much nectar! It was going to be awesome.

PHOTO: Setting up cameras on the dunes as the sun sets. — Here, we are setting up the site that will be filmed. (Photo: Patrick Alexander)

Until it wasn’t.

The sun set and we taped a handful of things: setting up the “moth sheet,” collecting floral scent, nectar, size measurements. And we waited and waited for the hawkmoths to show up; after about two and a half hours, we headed toward Carlsbad for the night. While I couldn’t imagine a better place for a hawkmoth to be, they clearly could.

PHOTO: Setting up a moth-catching framework at dusk. — Setting up the “moth trap”–a PVC frame with a bedsheet stretched over it. At night, a blacklight is turned on to attract night-flying insects (incuding hawkmoths) to the sheet. (Photo: Tim Kramer)

PHOTO: Cameraman filming the moth trap setup as the sun sets on the dunes. — In the dusky light we filmed the setup of our moth trap. (Photo: Tim Kramer)

PHOTO: Visitor Center entry to White Sands National Monument — White Sands National Monument (Photo: Krissa Skogen)

The following morning, we headed for White Sands National Monument, home of the world’s largest deposit of gypsum sand dune field, just west of Alamogordo, New Mexico. August 21 was a special night at White Sands—Full Moon Night. The park stays open until 11 p.m., and visitors come from near and far to experience the magic of the white sands by moonlight—which was one of the main reasons we were there. The flowers of the Hartweg’s sundrops glow in the moonlight and are very easy to see when the moon is full, by us as well as their hawkmoth pollinators.

After checking in with the National Park Service office, we set out to find Hartweg’s sundrops. The dunes provided the perfect white backdrop to capture hawkmoths visiting the flowers. Usually it’s hard to follow an individual moth at dusk; they become lost in the vegetation unless they’re quite close to you. At White Sands, you could follow an individual hawkmoth easily, from flower to flower, plant to plant—that is, if they showed up.

PHOTO: Sunset at White Sands National Monument. — The sun sets at White Sands National Monument–we eagerly anticipate the arrival of the moths and the full moon. (Photo: Krissa Skogen)

For a second night, we were out at the golden hour. Everything was beautiful, bathed in the light of the setting sun. We were feeling optimistic. Considering that this was our last chance to capture moths on film, we were prepared to stay as late as necessary. Looking around at everyone, I realized just how lucky I was, how lucky we all were to be there, together, at this incredible place, on what was sure to be an incredible night. Could we also be so lucky as to be graced by the presence of hawkmoths? We had come so far to capture this moment, and I have experienced many nights when conditions seemed ideal for hawkmoths to show up, only to be stood up instead—like the night before, at Yeso Hills.

PHOTO: Filming the episode in the dark. The moth trap provides a backlight for the "cast." — Krissa and Chris catch hawkmoths and discuss their role in pollination of Hartweg’s sundrops and other night-flowering plants. (Photo: Tim Kramer)

Before long, the sun had dropped over the horizon and the timing seemed right. I mentioned to Chris that I wouldn’t be surprised if we started to see some hawkmoths. As if on cue, a moth flew right by Chris’s head, close enough for him to hear its papery wings fluttering about—all as the camera was rolling! To say I was excited is an understatement. One moth turned into two…three…six…ten—visiting flowers, drinking nectar, and picking up pollen on their tongues, faces, and bodies, moving it from flower to flower—doing the ever-so-important job of pollination. You see, these plants will not produce fruits or seeds on their own—they require pollen from a different plant to do so, and that pollen has to be transported by a pollinator.

So after much nervous anticipation, the hawkmoths had arrived. And now you can see the full episode and how our adventures fit together into a nice story about desert plants that flower at night and their hawkmoth pollinators!

PHOTO: Pinned specimen of Hyles lineata. — White-lined sphinx moth (*Hyles lineata).* Just after sunset, a number of moths started to visit flowers, as if on cue! (Photo: Krissa Skogen)

Many thanks to Chris, Tim, and Paul, for being so incredibly fantastic to work with, and Mike, Norm, Hilda, Helga and Patrick, from whom I learned a great deal about the New Mexico flora and gypsum endemism. Thank you to Sophia Siskel and the Chicago Botanic Garden for providing financial and institutional support. This trip was truly the experience of a lifetime.

The Evolution of a Research Idea

Five years ago this past May, I found myself starting a new job and a new research project. My job, of course, was as a conservation scientist here at the Chicago Botanic Garden, and the research project had me sitting on the side of a road at dusk in Pueblo West, Colorado. I sat there in front of a group of plants that produce lovely-smelling flowers, waiting for their impressive pollinators to show up. And when they did, I snapped some of my very first photos of these beauties: hawkmoths, better known as the five-spotted hawkmoth, or to the scientific community as Manduca quinquemaculata.

PHOTO: Night photo of hawkmoth sipping nectar from evening primrose. — A five-spotted hawkmoth (*Manduca quinquemaculata*) drinks nectar from the Colorado Springs evening primrose (*Oenothera harringtonii*) as the flower begins to open. Pueblo West, Colorado, May 2008. Photo: Krissa Skogen

Just this past Friday, I visited the National Science Foundation’s Dimensions of Biodiversity Program, to find this very same photo—and the research that my colleagues and I will conduct over the next five years—highlighted.

So how did this one photo go from being taken in the spring of 2008 to being highlighted on the NSF’s website? How does a research project evolve and grow over time? Ask any scientist what they are currently working on and their answer will almost always start with, “I was first fascinated by x back in y….” Something caught their attention, sparked a thought, pulled them in—and they continued asking question after question, developing hypotheses and gathering data to test them, with their answers pushing them forward, sometimes down unanticipated paths, and sometimes into much bigger or smaller arenas. The more one knows, seemingly, the less one knows; old questions are answered and new ones are developed. This is what pushes scientists, and science, forward.

The evolution of a research idea

PHOTO: Krissa Skogen poses with primrose in New Mexico. — Krissa Skogen poses with an evening primrose in New Mexico. Photo: Chris Martine

In 2008, I started my current research program. After many conversations with Rob Raguso (Cornell University) and Tass Kelso (Colorado College), I drove out to Colorado with a plan to collect as much information on as many different populations of the Colorado Springs evening primrose (Oenothera harringtonii) as possible in a short period of time. That year, my timing was off—I arrived in Colorado on June 10. Oenothera harringtonii flowers primarily in May. Most of the plants had stopped flowering and so instead of collecting data on floral features, nectar, scent, and pollinators, my field assistant, Evan Hilpman, and I collected data on plant size, health, reproductive success (how many fruits did they produce?) and population size (much like a census). And one striking thing we noticed was this: small white “galls” on some of the green, developing fruits. We took notes on how often we saw this, never anticipating the importance that these little white dots would play in just a few years’ time.

PHOTO: Closeup image of a tiny, white foamy-looking dot (one of many) on a host plant. — We noticed small white “galls” on some of the green, developing fruits. These are parts of the cocoons of tiny little moths, called microlepidopterans, of the genus *Mompha*. Photo: Krissa Skogen

In subsequent years this project grew, and in the last four years—with the help of conservation scientist Jeremie Fant and other colleagues, and many research assistants and students—we’ve collected data on flower size, nectar volume and sugar content, floral scent, who pollinates and when (hawkmoths come at dusk and visit overnight; bees generally visit in the morning), how populations grow and shrink over time, which other plant species are flowering at the same time, and more. We know a lot of things about this species now, and one thing has been a constant: those little white balls have been observed year-in and year-out in some populations, but not in others.

We know now that some of our populations have an important compound—linalool—and some do not. We know that genetically speaking, our 25 populations function more like three, likely due to the fact that hawkmoths can fly so darn far (some estimates are up to 20 miles in just one night). And more recently, we started gathering more data on those little white balls. It turns out that they are parts of the cocoons that surround the larvae of tiny little moths called microlepidopterans, which belong to the genus Mompha. These moths lay their eggs on flower buds, fruit, and stems. If the larvae eat flower buds and/or seeds, they reduce the number of offspring that the plant produces. This is bad for any plants upon which these moths decide to lay their eggs, but everything must eat, right?

PHOTO: Trio of photos of each life stage of the moth: adult, larva, and cocoon. — *Mompha stellella* microlepidopteran adult; larva inside fruit (seed predator); cocoon inside *O. harringtonii* fruit. Photos: Terry Harrison and Krissa Skogen

In speaking with colleagues across the country and in Canada (plant and moth experts, alike), we developed an intriguing story and series of hypotheses we felt were compelling. Do pollinators and floral antagonists both respond to the same attractive scent? Could floral scent be telling hawkmoths and Mompha moths where the flowers are? Pollination is good for plant reproduction, but anything that eats flowers or seeds is not—so how would this trade-off play out in evolutionary time?

These questions have led us to the project that we will pursue on a much larger scale, thanks to recently awarded funding from the National Science Foundation’s Dimensions of Biodiversity Program for our proposal, titled “Landscapes of linalool: scent-mediated diversification of flowers and moths across western North America.”

PHOTO: Bee coated in pollen, inside primrose bloom. — A *Lasioglossum* species bee robbing pollen from *O. harringtonii* at dawn. Photo: Sadie Todd

Relationships among flowering plants and insects represent one of the great engines of terrestrial diversity. Floral scent and other plant volatiles are important drivers of these relationships (e.g., pollination, herbivory, plant defense), but remain poorly integrated into floral evolution and pollination ecology. Few studies have tested the spectrum of plant fitness outcomes when scent attracts both pollinators and floral/seed enemies. Thus, the hidden diversity of floral/seed predators and their potential as selective agents constitutes a considerable gap in pollinator-centric understanding of floral evolution. These “forgotten predators” have co-diversified with flowering plants and are likely influential in the evolution of most plant-pollinator interactions.

PHOTO: Five-spotted hawkmoth extending its proboscis (longer than its body) into a primrose bloom as it hovers. — A five-spotted hawkmoth (*Manduca quinquemaculata*) probes an opening evening primrose flower for nectar with its proboscis. Photo: Krissa Skogen

This project is ambitious and large and pulls upon a wide variety of expertise. In total, there are 11 Ph.D. scientists collaborating on it, including myself, Jeremie Fant, and Norm Wickett here at the Garden. The others include Robert Raguso (Cornell University), Rachel Levin (Amherst College), Terry Harrison (University of Illinois at Urbana-Champaign), Jean-Francois Landry (Agriculture & Agri-Food Canada, Eastern Cereal and Oilseed Research Centre), Sylvia (Tass) Kelso (Colorado College), Kathleen Kay (University of California, Santa Cruz), Mike Moore (Oberlin College), and Warren Wagner (Smithsonian Institution).

We are excited about what we’ll uncover in the next five years and will update you with progress as our discoveries unfold!

News from Conservation and Land Management Interns

The hiring process for the 2013 Conservation and Land Management (CLM) Internship Program is nearly complete, and newly hired interns are just beginning their experiences in unique locations across the western U.S.!

*Sclerocactus glaucus*, endemic species of western Colorado, in bloom (Photo ©Peter Gordon)

Since 2001, the Chicago Botanic Garden and many federal agencies (Bureau of Land Management, National Park Service, U.S. Fish and Wildlife Service, USDA Forest Service, and U.S. Geological Survey to name a few) have combined their strengths to train more than 700 college graduates through the CLM program, primarily in 13 western states. These internships involve work in botany and wildlife-related fields, or combinations that may include monitoring or assessing threatened and endangered species and habitats. As 2013 CLM interns begin a new journey, many of last year’s interns are finishing up, and still others continue their internship experiences into spring. Three interns recently shared their thoughts and experiences on the CLM blog:

Lauren Stevens worked in Phoenix, Arizona, and reflects on her time there with a poem.
Carson Moscoso just started his internship in Las Vegas, Nevada, and explains the excitement of upcoming fieldwork.
Darnisha Coverson, an intern in Lakewood, Colorado, tells about the duties of an intern during the winter months.