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How Did the Bumblebee Get Its Stripes?

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How Did the Bumblebee Get Its Stripes?

Heather Hines

UNIVERSITY PARK, Pa. -- Say the word, “bumblebee,” and most people in the eastern United States will envision a fuzzy, pollinating insect with yellow and black bands. To a person in the Rocky Mountains, however, the image—while similar—will also have a bright orange band set among the yellow and black.

It turns out this color difference is not indicative of two separate species as one might expect. Instead, each of the color patterns comprises numerous species of bumblebee that have converged on one “look” as a way of avoiding predation.

According to Heather Hines, assistant professor of biology and entomology, bumblebees are distasteful to predators because of their sting and they mimic each other to avoid being eaten. “By looking like each other wherever they co-occur, bumblebee species enhance the warning signal to predators that they are distasteful,” she said. “It reduces predation overall.”

Hines noted that mimicry patterns of bumblebees vary with region of the world. “Through processes like mimicry, these bees have undergone an exceptional natural radiation, exhibiting hundreds of different body color patterns across the globe,” she said.

Hines has received an $817,000 Faculty Early Career Development (CAREER) award from the National Science Foundation to study the genetics of color-pattern variation and mimicry among bumblebees. According to her, scientists know why bumblebees mimic each other, but little is known about how they do it. With the CAREER award, Hines plans to investigate the genetics underlying color-pattern variation and how these patterns have evolved through time.

“One of my main goals is to investigate how exceptional diversity can be achieved at a genetic level,” said Hines. “Overall, we have very little understanding of how most functional traits are genetically coded. We’re trying to figure out how changes in traits—like color pattern—happen genetically to understand how evolution can happen.”

Hines is particularly interested in examining whether all species of bumblebee use the same gene(s) to create color variation, and, if they do, whether this came about through a single mutation that was selected for and has been maintained across populations through time or whether separate species independently evolved the use of the same gene(s).

According to Hines, a set of genes, known as Hox genes, is known to be involved in specifying segments of the bumblebee body. “Because the color pattern of bumblebees is segmental, Hox genes, or genes related to Hox genes, may be involved in turning on and off pigments in these segments,” she said. “Part of our goal with the grant is to examine the role of such genes in driving the variation in pigmentation.”

To answer these questions, Hines will combine field work—including characterizing the distribution of bumblebee species and color patterns throughout the United States by collecting live specimens and examining museum specimens—with lab work. She also will enlist undergraduate students to help provide data.

“This project will involve creating a module for analytical chemistry classes at Penn State that will enable students to discover new pigments across insects,” said Hines. “This allows novel discovery in the classroom, and we hope to be able to publish some of the results.”

The end result of the project could be a thorough understanding of how pigmentation develops in bumblebees and how the insects alter this process to adapt to their environment.

“Ultimately,” said Hines, “understanding the genetics underlying traits tells us how the differences across life came to be at the raw mechanistic level, as well as the constraints and opportunities our molecules pose in the ability to attain different forms.”