Evening Primroses, Pumps, and Pollinators

Undercover Science

Julianne Beck —  May 16, 2016 — 1 Comment

Rick Overson is fascinated with insects—especially the kinds that love desert climates like in Arizona, where he grew up and earned his Ph.D. in biology. After completing a postdoctoral assignment in northern California, he decided it was time to get to know the little buggers even better, so Dr. Overson hopped on a plane for Chicago and stepped out into the subzero temperatures of the polar vortex to do just that.

PHOTO: Dr. Rick Overson with hawkmoth specimens.

Dr. Rick Overson with hawkmoth specimens

The devoted entomologist didn’t expect to see the insects in Chicago, but he was eager to join research at the Chicago Botanic Garden. A multidisciplinary team was assembling there to look for scent variations within Onagraceae, the evening primrose family, and connections from floral scent to insect pollinators and predators. The findings could answer questions about the ecology and evolution of all insects and plants involved. Overson is a postdoctoral researcher for the initiative, along with Tania Jogesh, Ph.D.

“Landscapes of Linalool: Scent-Mediated Diversification of Flowers and Moths across Western North America” is funded by a $1.54 million Dimensions in Biodiversity grant from the National Science Foundation. The project is headed by Garden scientists Krissa Skogen, Ph.D., Norman Wickett, Ph.D., and Jeremie Fant, Ph.D. It was developed from prior research conducted by Dr. Skogen on scent variation among Oenothera harringtonii plants in southern Colorado.

“For me, the most important thing coming out of this project is documenting and showing this incredible diversity that happens inside a species,” said Overson. “It’s vitally important for me to break down this idea of a species as a discrete unit. It’s a dynamic thing that is different in one place than another. That factors into conservation and our understanding of evolution.” In this case, he and his colleagues theorize that the evolution of the insect pollinators and predators is connected to the evolution of the scent of the plants.

PHOTO: Evening primrose in bloom on the plains of New Mexico.

Evening primrose in bloom on the plains of New Mexico. Photo by Dr. Rick Overson

The first two years of field work brought Overson back to his desert home. He traveled across Arizona, Utah, and nearby states with a group of about five scientists during summer months when the flowers were blooming. The team visited several populations each of 16 species of flower for a total of 60 locations. Overson and the team identified and documented the insects visiting the plants and compiled scent chemistry from the flowers. Their tool kit included a pump to pull the scent from a flower onto tiny polymer beads that held the scent inside of a vial. From there, they extracted the scent chemicals at the end of the research day or night. “It’s definitely the case that this pattern of scent variation inside a species is very common in this group,” he said of the team’s preliminary findings.

PHOTO: Hawkmoth on evening primrose.

A beneficial pollinator, the hawkmoth, visits an evening primrose (Oenothera harringtonii).

In the field they also took video recordings of pollinator behavior to see who visited which flowers and when. The pollinators, including hawkmoths and bees, follow scents to find various rewards such as pollen or nectar. The insects are selective, and make unique choices on which plants to visit.

Why do specific pollinators visit specific plants? In this case, the Skogen Lab is finding that it is in response to the scent, or chemical communication, each flower releases. “In the natural world those [scents] are signals, they are messages. Those different compounds that flowers are producing, a lot of them are cocktails of different types of chemicals. They could be saying very different things.”

PHOTO: Closeup of a wasp on a closed evening primrose bloom.

Nature is complicated. Here, a wasp lays eggs through a flower bud into a hidden Mompha moth inside. Its larvae will eventually destroy both the moth and the flower. Photo by Dr. Rick Overson

A destructive micromoth called a microlepidopteran (classified in the genus Mompha), has also likely learned how to read the scent messages of its hosts. The specialist herbivore lays eggs on plants leading to detrimental effects for seed production. The team’s field work has shown that Mompha moths only infect some populations of flowers. When and why did the flowers evolve to deter or attract all of these different pollinators? Or was it the pollinators who drove change?

At the Garden, Overson is currently focused on exploring the genomes, or DNA set, of these plants to create a phylogeny, which looks like a flow chart and reads like a story of evolution. “Right now we don’t know how all of these species are interrelated,” he explained. When the phylogeny is complete, they will have a more comprehensive outline of key relationships and timing than ever before. That information will allow scientists to determine where specific scents and other traits originated and spread. He will explore the evolution of important plant traits using the phylogeny including the color of the flowers and their pollinators, to answer as many questions as possible about relationships and linked evolutionary events.

In addition, the team is looking at population genetics so they can determine the amount of breeding occurring between plant locations by either seed movement or by pollinators. They will also look for obstacles to breeding, such as interference by mountain ranges or cities.

“Relationships among flowering plants and insects represent one of the great engines of terrestrial diversity,” wrote principal investigator Krissa Skogen, PhD, in a blog post announcing the grant.

The way that genes have flowed through different populations, or have been blocked from doing so over time, can also lead to changes in a species that are significant enough to drive speciation, or the development of new species, said Overson. “The big idea is that maybe these patterns that are driving diversity within these flowers could ultimately be leading to speciation.”

By understanding these differences and patterns, the scientists may influence conservation decisions, such as what locations are most in need of protection, and what corridors of gene flow are most important to safeguard.

PHOTO: Dr. Rick Overson in the field.

Dr. Rick Overson in the field

“We absolutely can’t live without plants or insects, it’s impossible,” remarked Overson. “Plants and insects are dominant forces in our terrestrial existence. Very few people would argue that we haven’t heavily modified the landscape where these plants and insects live. I think it is crucially important to understand these interactions for the sake of the natural world, agriculture and beyond.”

When Dr. Overson is taking a break from the laboratory, he visits the Desert Greenhouse in the Regenstein Center, which feels like home to him.


©2016 Chicago Botanic Garden and my.chicagobotanic.org

“Baltimore oriole,” my husband Chuck called out—and there it was, its orange coloring glowing so brightly in the morning sun that it seemed lit from within. The bird almost seemed to be posing for us, perching in full view on a nearby tree branch and bobbing its black head as it sang.

Al Stokie, our expert birding companion, recorded it in his notebook; it would become part of the weekly bird survey he supplies to the Chicago Botanic Garden.

We continued on our walk through a wonder of the natural world that anyone in the Chicago area can see for the price of a pair of binoculars: spring bird migration.

Every spring, small, colorful warblers fly through the Chicago area on their way from their winter homes in Central and South America to their nesting grounds in the northern United States, Canada, and as far north as the Arctic Circle. And every year, birders at the Garden and beyond delight in the sight.

“In May, you always go crazy,” said Stokie, who has become the official compiler of the Garden’s bird statistics.

Cape may warbler.

Cape May warbler

Blackburnian warbler.

Blackburnian warbler

But May isn’t just for experienced birders; the birds are so numerous and their breeding plumage so gorgeous that it’s a perfect time for anyone to explore bird-watching. The 385 acres of the Garden are an excellent place to start. “The Garden is a pretty well-known spot for birding,” said Jim Steffen, the senior ecologist who oversees the Garden’s bird-friendly practices and its cumulative bird list, which currently numbers 255 species.

Come #birdthepreserves with the Forest Preserves of Cook County. View the list of upcoming events for free events near you.

FPDCC Bird of the Month chart.

Learn about the bird of the month at birding events at your local forest preserves.

And this year, the Garden is partnering with the Forest Preserves of Cook County’s #birdthepreserves initiative. There are events at the preserves, and a different bird is featured each month. (In May, it’s the Baltimore oriole.) There’s even a good-natured competition to see which site can record the most bird species. 

Where to look for birds at the Garden? It depends.

“You bird the Garden at different times of the year in different places,” Stokie said. “May is warbler month, and warblers are found in the woods.” So he started us off in the McDonald Woods, in the Garden’s northeast corner. We walked along the wood-chipped path, and on boardwalks and bridges over streams and ephemeral ponds, watching for movement in the trees. It was a blustery morning. “Our problem today is going to be the wind,” Stokie said, and he was right. We saw blue-gray gnatcatchers, catbirds, ovenbirds, and that beautiful oriole. And when we got to a small forest pond, we saw a solitary sandpiper scurrying through the water on its stick-like legs.

Stokie saw far more than I did—he recorded 48 species—but we didn’t get the full-on spring migration blast of birds.

You might, though.

The peak of spring migration is typically May 10 – 20, and International Migratory Bird Day is May 14. Most of the warblers will still be moving through in the next few weeks, Steffen said, and there should be flycatchers, goldfinches, woodpeckers, and orioles. Around the Garden Lakes, he said, people can see wood ducks, mallards, night herons, green herons, and great blue herons.

Great blue heron.

Great blue heron

Ruby-crowned kinglet.

Ruby-crowned kinglet

It’s a grand sight. But along with the beauty, Steffen sees cause for concern due to climate change. Trees are leafing out earlier, before the warblers—cued by the lengthening of days—arrive. “The buds are already open, and the insects associated with them are gone,” Steffen said. “It’s messing up the synchronization.”

The best places to see birds at the Garden in spring, Stokie says, depend on the bird. Warblers and vireos will be in woodlands like the McDonald Woods and the Barbara Brown Nature Reserve at the Garden’s southeast corner. Sparrows will be in open areas like the Dixon Prairie; and shorebirds and late migrating ducks will be found in the wet areas just north of Dundee Road.

Hairy woodpecker.

Hairy woodpecker

Sign up for a bird walk with an expert. The Garden will have a spring migration walk on May 21. 

Or go to any forest preserve or park. Look for people with binoculars, and ask what they’re seeing. You’ll be off and birding.


©2016 Chicago Botanic Garden and my.chicagobotanic.org

Attention orchid fans: our vanilla orchid is blooming in the Tropical Greenhouse at the Chicago Botanic Garden. It’s a rare occurrence in the wild—and in a greenhouse. Wade Wheatley, assistant horticulturist, seized the moment to hand-pollinate the flower. 

Vanilla planifolia before pollination

Vanilla planifolia before pollination

Why hand pollinate? In hopes of producing a vanilla bean. Yes, the fruit of a vanilla orchid is used to make pure vanilla extract, which flavors many foods we enjoy.

Vanilla vines typically begin to flower at five years or older. Flowers are produced in clusters, with one flower opening each day in the morning. Stop by the Tropical Greenhouse soon to see what’s in bloom. 


©2016 Chicago Botanic Garden and my.chicagobotanic.org

It is our responsibility as citizens, but especially as practitioners in the fields of horticulture and botanical sciences, to be good stewards of the land and ensure that what we are growing in our backyards and at the Chicago Botanic Garden will not contribute to problems in the future. That is why the Garden recently replaced the callery pears at the entrance to the Visitor Center.

In addition to the callery pear, the Garden also removed winged euonymus (Euonymus alatus) and tamarisk (Tamarix spp.).

Callery pear and euonymous plantings at the Visitor Center entrance in autumn of 2010.

Callery pear and euonymus plantings at the Visitor Center entrance in autumn of 2010.

One threat to our natural world is invasive plants. While many of these plants may on the surface appear to be attractive additions to the landscape, they can force out native species. Short of complete destruction of a natural area, I cannot think of anything more unsightly than a natural area that has been completely consumed by an invasive species to the point that it is no longer recognizable and holds very little biodiversity.

The list of invasive plants and potentially invasive plants is not set in stone; it is an evolving list and one that will continue to change as our climate changes. The callery pear (Pyrus calleryana) was not on the invasive species lists for our region a decade ago, but today it is in Illinois, along with Alabama, Georgia, South Carolina, and Tennessee. Most are familiar with the cultivar ‘Bradford’, but there are several others, including ‘Aristocrat’, ‘Autumn Blaze’, and ‘Cleveland Select’.

Garden staff plant non-invasive American yellowwood (Cladrastis kentukea) at the entrance to the Visitor Center.

Garden staff plant non-invasive American yellowwood (Cladrastis kentukea) at the entrance to the Visitor Center.

This spring we replaced all of the Pyrus calleryana ‘Autumn Blaze’ at the front entrance of the Visitor Center with the non-invasive American yellowwood (Cladrastis kentukea). As a result, the front entrance is noticeably more open in appearance, and the low canopy and refreshing shade that existed in years past is now gone; it will return as the plantings grow.

Although both of these species are medium-sized deciduous trees with white flowers, the yellowwood has different ornamental characteristics. The callery pear flowers in the early spring, while the yellowwood flowers in late spring to early summer. The callery pear has unrivaled fall color in shades of red, orange, and yellow, while the yellowwood is one of the best for yellow fall color. 

Why is the callery pear called an invasive?

This pear has abundant seeds that can be carried by birds to natural areas. Plants can then become established, thus displacing native species. As land stewards, the Garden is very mindful of prohibiting and eliminating any plants known to be invasive in our region.

The new plantings at the Visitor Center entrance.

The new plantings at the Visitor Center entrance will take time to grow, but will someday provide the shade and fall color of their predecessors.

I have no doubt that some of these recently removed invasive plants were favorites among Garden visitors, our staff included. But sometimes what we like isn’t always good for us, or good for the environment.

New seasonal plantings replace the previous shrubs in the entry beds.

New seasonal plantings replace the previous shrubs in the entry beds.

I encourage you to review and continue to consult invasive species lists, including on the invasive.org website, and do your part by removing invasive species from your garden and resist purchasing and adding more. There are so many benign, beautiful options available to gardeners, and the Garden, along with numerous other organizations, has done the work for you by listing alternatives for the invasive plants that we feel we cannot live without. View a list of our recommended alternatives to invasive plant species here

Each of us can play an important role in preserving the natural landscapes for future generations.


©2016 Chicago Botanic Garden and my.chicagobotanic.org

The landscape of northern Illinois has some remarkable features, many of which are remnants of a glacial past. The Chicago Botanic Garden takes advantage of its islands and lakeshore, and the Alliance for the Great Lakes helps to explore and protect the area’s unique and beautiful ravines.

Help shape a healthy future for your local ravines—home to native trees, wildflowers, birds, and butterflies; pathways to Lake Michigan beaches, and scenic backdrops for parks and homes. Learn about erosion that may threaten some of these ravines, as well as such concerns as damage to sewer lines, roads, and bridges. Ask questions, hear from experts, and brainstorm with your neighbors at this workshop that is open to ravine homeowners, ravine experts, local officials, and everyone who cares about the ravines in our community.

PHOTO: Ravine Openlands Lakeshore Preserve — MarwenRegister now for Revitalizing Our Ravines, a community workshop at the Garden on Wednesday, June 1, from 12:30 to 7:30 p.m. Experts will speak about how you can help protect and restore ravines. Local landscape and ravine restoration service providers will show examples of ravine restoration and landscaping.

Complimentary snacks, refreshments, and an evening cocktail hour are included with registration for this event. Registration closes on May 30.

Hosted by the Alliance for the Great Lakes, the Chicago Botanic Garden, Openlands, and the Field Museum.


©2016 Chicago Botanic Garden and my.chicagobotanic.org