Wildflower Colors Tell Butterflies How To Do Their Jobs

The recipe for making one species into two requires time and some kind of separation, like being on different islands or something else that discourages gene flow between the two budding species.

In the case of common Texas wildflowers that share meadows and roadside ditches, color-coding apparently does the trick.

Duke University graduate student Robin Hopkins has found the first evidence of a specific genetic change that helps two closely related wildflowers avoid creating costly hybrids. It results in one of the normally light blue flowers being tagged with a reddish color to appear less appetizing to the pollinating butterflies which prefer blue.

"There are big questions about evolution that are addressed by flower color," said Hopkins, who successfully defended her doctoral dissertation just weeks before seeing the same work appear in the prestigious journal Nature.

What Hopkins found, with her thesis adviser, Duke biology professor Mark Rausher, is the first clear genetic evidence for something called reinforcement in plants. Reinforcement keeps two similar proto-species moving apart by discouraging hybrid matings. Flower color had been expected to aid reinforcement, but the genes had not been found.

In animals or insects, reinforcement might be accomplished by a small difference in scent, plumage or mating rituals. But plants don't dance or choose their mates. So they apparently exert some choice by using color to discourage the butterflies from mingling their pollen, Hopkins said.

Where Phlox drummondii lives by itself, it has a periwinkle blue blossom. But where its range overlaps with Phlox cuspidata, which is also light blue, drummondii flowers appear darker and more red. Some individual butterflies prefer light blue blossoms and will go from blue to blue, avoiding the dark reds. Other individual butterflies prefer the reds and will stick with those. This "constancy" prevents hybrid crosses.

Hybrid offspring between drummondii and cuspidata turn out to be nearly sterile, making the next generation a genetic dead-end. The persistent force of natural selection tends to push the plants toward avoiding those less fruitful crosses, and encourages breeding true to type. In this case, selection apparently worked upon floral color.

Hopkins was able to find the genes involved in the color change by crossing a light blue drummondii with the red in greenhouse experiments. She found the offspring occurred in four different colors in the exact 9-to-3-to-3-to-1 ratios of classical Mendelian inheritance. "It was 2 in the morning when I figured this out," she said. "I almost woke up my adviser."

From there, she did standard genetics to find the exact genes. The change to red is caused by a recessive gene that knocks out the production of the plant's one blue pigment while allowing for the continued production of two red pigments.

Even where the red flowers are present, about 11 percent of each generation will be the nearly-sterile hybrids. But without color-coding, that figure would be more like 28 percent, Hopkins said. Why and how the butterflies make the distinction has yet to be discovered.

Hopkins will be continuing her research as a visiting scientist at the University of Texas, and the clear message from all of her advisers is "follow the butterflies. Everyone wants to know more about the butterflies!"

The research was supported by grants from the National Science Foundation.

By Karl Leif Bates

CITATION:
"Identification of two genes causing reinforcement in the Texas wildflower Phlox drummondii," Robin Hopkins and Mark D. Rausher. Nature, Advance Online Publication, Jan. 9, 2011 DOI:10.1038/nature09641

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Female monarch butterflies on 30-year decline in eastern North America

Female monarch butterflies in eastern North America have significantly declined over the past 30 years, a new study by a University of Georgia researcher reveals.

Andy Davis, a Ph.D. candidate in the Warnell School of Forestry and Natural Resources, analyzed published overwintering and migratory data for the insect from 1976 to the present, discovering that the female to male ratio for the butterflies east of the Rockies has gradually been changing. In the late 1970s, Davis said, females made up around 53 percent of the monarch butterfly population that migrated to Mexico for the winter. Today, that number has dropped to about 43 percent which paints a dire picture for population recruitment. Davis outlines his findings in a new paper co-authored with Eduardo Rendón-Salinas of World Wildlife Fund-Mexico. The paper appears in Biology Letters, rsbl.royalsocietypublishing.org.

“I nearly fell over when I saw the trend,” said Davis. It was an unintentional but extremely important finding.”

The monarch butterfly, one of the most well-known and widely-recognized insects in the world, is a flagship species for conservation. North American Monarchs can migrate more than 2,000 miles as they fly to Mexico from Canada and the U.S. for the winter. “The implications of this decline are huge,” Davis said. “Female monarchs can lay as many as 400 eggs over their lifetime, which is why the species is so resilient.”

But Davis said that as the monarch population continues to struggle because of breeding habitat loss, widespread pesticide use, and deforestation of the overwintering sites, losing a significant number of females could seriously hinder the population’s ability to rebound after periodic crashes. Davis, who studies monarchs in addition to his doctoral work, said that news of the decline has gone unnoticed until now “because no one’s ever looked at the data like this. For years, scientists have been collecting male and female monarchs at the overwintering sites and during the fall migration. When we compiled the numbers from these collections, along with the year they were made, the trend was obvious.”

At their wintering sites, monarchs cluster on trees and form massive colonies that can number in the millions. Illegal logging of these trees is a serious threat to their wintering stage, but the threats they face in their breeding range in the United States and Canada are just as important. Further, because the decline in females is also present in the fall migration, Davis says, it means that whatever is causing this decrease is happening during the breeding season in the U.S. and Canada.

“That tells us we need to look here to see what the cause is,” he said. Whatever it is, Davis explained, “it must be something that affects females more so than males. This will be the challenge for future studies to sort out. We’ll also need to monitor the numbers of females in the population closely over the next few years, at all stages of their life cycle.

This discovery just goes to show how new insights can be gained from critical re-examination of published studies, and more generally, how much we still need to learn about this amazing insect before it is too late.”

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Spring Planting Can Be for the Birds, and Butterflies

Spring means that backyard gardeners and landscapers are hard at work beautifying their yards. But in all of the bustle and planning, the Georgia Wildlife Resources Division recommends adding a place for wildlife, no matter the yard’s size.

Some tips:

** Plant fruit-producing shrubs like native crabapple, serviceberry, blueberries, strawberries, blackberries, dogwoods and wax myrtle. To attract songbirds including cardinals, robins, bluebirds, orioles, brown thrashers and mockingbirds, plant in clumps, clusters or islands. Cover provides nesting areas for birds and small mammals, as well as shelter from predators and inclement weather.

** Always use caution when using pesticides. Overuse or misuse of lawn chemicals can harm wildlife. Contact a local Cooperative Extension Service with questions about amounts and types of pesticides to use.

** Create a pool as a birdbath and gathering place for wildlife. A pool can be as simple as a small pond or as elaborate as an in-ground reservoir with waterfalls. Also, shallow birdbaths make excellent landscaping focal points.

** Don’t forget the butterflies! Cultivate nectar-producing plants such as salvia, lantana, butterfly bush, milkweeds, blazing star, impatiens and verbena to provide butterfly-viewing opportunities and add an array of color to backyard habitats. Planting butterfly larval host plants like hollyhock, fennel, violets, pawpaw and asters will also encourage butterflies to come to your garden and help them complete their life cycles.

** Use native plants as much as possible. Native wildlife is adapted to the plants, and the plants are adapted to surviving under local conditions with little need for extra fertilizer or water.

** Remember the field guide and binoculars. Watching wildlife can be fun for the entire family, especially considering Georgia’s rich diversity of wild animals and plants. Close-focusing (6 feet or less) binoculars allow you to observe butterflies up close. Field guides featuring birds and butterflies are great resources in helping identify species.

With proper planning, any yard can feature trees, shrubs and other plants that will provide food, shelter and habitat for wildlife. For more information on spring planting for birds and butterflies, visit Wildlife Resources’ Web site, www.georgiawildlife.com, click “Conservation” and choose “Wildlife in Your Backyard.”

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Planting for Pollinators

Butterflies, hummingbirds, bees and even bats and flies are all pollinators that feed off plants in your yard. So when you’re adding new flowers to your landscape, choose those that provide nectar and pollen for winged workers.

“Almost all native plants that rely on pollination rely on these limited numbers of insects,” said Paul Thomas, a horticulture professor at the University of Georgia College of Agricultural and Environmental Sciences. “Plants that attract pollinators provide food for the insects. But they’re not just helping the plants in your gardens. They are helping all native plants.”

Pollinators are vital to agriculture. They pollinate most fruit, vegetable and seed crops. Healthy pollinator populations can improve plant and fruit size and quality. By adding plants to your landscape that provide food and shelter for pollinators through their active seasons, you can help the pollinators and help maintain the biodiversity of native species.

Attracting pollinators

Whether you hope to attract butterflies and hummingbirds to your home or provide a food source for honeybees, there are a few things to consider. Pollinators need consistent nectar sources, open roaming areas, tree-canopy cover nearby and a source of moisture and soil salts.
Select a sunny spot for a pollinator garden. “It is tough to plant a pollinator garden in the shade,” Thomas said. “To provide nectar and pollen, full-sun plants are the way to go.”

Salvia, lantana and trumpet vine will take the heat. Echinacea can tolerate drought conditions as well.

To extend the flower season, “plant the perennials you want, fill in with annuals and provide some full-summer blooming shrubs,” he said. “The more varied your garden the better.”

Thomas recommends hardy lantana, blue sage salvia, purple coneflower, verbena canadensis and thrift. A good native butterfly plant is Joe Pye weed, which provides fall blooms.

Pay attention to each plants' height, vigor and space accordingly. Miss Huff lantana and the butterfly bush Black Knight may look small the day you plant them. But each can grow into a 4-foot-wide bush.

Provide a variety of plant colors and shapes to attract multiple pollinators. Hummingbirds are attracted to red and blue flowers while bees tend to prefer white and yellow blooms. Butterflies are happy with pinks and purples.

Bees need rounded flowers where they can more easily reach the nectar and pollen. Butterflies can sip from tubular or cone shaped flowers.

Hummingbirds

Hummingbirds look for flags or certain plants that signal an appropriate feeding and breeding site.

“If a male hummingbird sees a native horse chestnut, he knows the area is a suitable habitat,” Thomas said.

Males are also attracted to bright red flowers like those on native honeysuckle. Later in the summer, young hummingbirds prefer flowers such as blue sage. Other recommended plants for hummingbirds are red flowering chestnut, abelias, summer phlox, chaste tree, columbine, cardinal flower, bee balm, red hot poker, hibiscus and most salvias.

Butterflies

“For a successful butterfly garden, it’s vital to select nectar-producing plants with accessible flowers,” Thomas said.

He suggests lantana and purple coneflower because they produce nectar and attract butterflies continuously, even during the driest droughts. Choose plants that will bloom in sequence, providing nectar from March 1 to the first killing frost.

Homestead purple verbena will bloom in early spring through early summer and flower again in late fall. This provides nectar for early- and late-season butterflies such as Question Mark, Red Admiral and Zebra and Tiger Swallowtails.

Blue anise sage and purple coneflower will bloom in cycles if you pick off the spent flowers. Verbena bonariensis will stop flowering early, but you can cut it halfway back in early August to stimulate new flowers for fall.

Having a food source for caterpillars is vital, too. To accommodate this early butterfly stage, include an ornamental fennel, the favorite food of Eastern Black Swallowtails. Dill, fennel, carrot and parsley do well, too.

By April Sorrow
University of Georgia

April Sorrow is a news editor for the University of Georgia College of Agricultural and Environmental Sciences.

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