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The Evolution of Butterfly Vision

During the spring and summer months, many people enjoy gazing at brightly colored flowers and the butterflies that frequent them, but few of us stop to consider: what do the butterflies see?

A few evolutionary biologists have pondered that question, and through research have uncovered a possible--and if it exists, surprising--link between the evolution of color vision in butterflies and in humans. One of those researchers is Adriana Briscoe (pictured left), an assistant professor in the Department of Ecology and Evolutionary Biology at the University of California, Irvine, and a Latina scientist. Briscoe’s lab is one of a few worldwide studying the evolution of red-green color vision in butterflies and their closest relatives, moths and skippers. Research suggests that a gene duplication event, similar to the one that produced color vision in primates--humans, chimps, and gorillas--may have occurred in butterflies.

Phenotypic variation in the visual system of butterflies is just one of many areas that scientists may explore in molecular evolution and evolutionary physiology. Briscoe believes that evolutionary biology is an important--and growing--discipline that will continue to offer a range of career opportunities. “The field is going to expand because of the usefulness of evolutionary theory for all areas of biology,” she says. “The biomedical sciences will become increasingly reliant on a group of well-educated people who can deal with genome sequence analysis and, for example, make predictions about the evolution of diseases, such as avian flu.”

Briscoe's field site, Tioga Pass Road, Eastern Sierra Nevada, California

The Origins of Life--and a Career

Briscoe credits her parents with instilling in her a deep love of reading. But, she says, it was religion--her catechism studies especially--that provoked her interest in science. “I was raised Catholic, so I became interested in ethics, philosophy, and origins of the universe, and that kind of spun into my current interests in natural sciences.”

Briscoe was educated in the public schools of southern California and entered Stanford University in the fall of 1988, taking the maximum number of credits each quarter and earning three degrees: a B.A. in philosophy in 1992, a B.S. in biological sciences in 1993 (both with departmental honors), and an M.A. in philosophy, also in 1993. Her philosophy training, says Briscoe, helped her to become a clear and concise writer, which comes in handy when writing grants and scientific papers.

Briscoe decided to pursue a Ph.D. related to Darwinian evolution. The discipline has lots of well-respected academicians, but Harvard had two of the field's best-known thinkers-- Stephen Jay Gould and Richard Lewontin. So Briscoe traded coasts and headed to Cambridge, Massachusetts. “Gould and Lewontin were not only giants in evolutionary biology, but also in philosophy of biology,” Briscoe explains. “I had been trained in philosophy of biology at Stanford, and I was very interested in working with Lewontin in particular.”

After finishing her Ph.D. in 1999, she completed two postdocs--at the University of Arizona and the University of Colorado, Denver--before gaining a faculty appointment at the School of Biological Sciences at UC-Irvine.

Preparing for Success

Successful careers in evolutionary biology don’t happen overnight; lots of planning and hard work must come first. Briscoe has some advice to first-year grad students, postdocs seeking employment, and first-year assistant professors in the field.

  • Graduate Students—Be as broadly trained as possible and look at the big picture rather than focusing too quickly on a particular area of research. Also important is exposing yourself to new ideas, those that differ from what you are comfortable or familiar with. Take field-based courses at other institutions and religiously attend departmental seminars and journal clubs.

  • Postdocs—Understand that search committees are looking for individuals whose work will not only stand out from the crowd, but will also provide a foundation for others to build upon. Remember that during your interview, they are trying to determine if they want to run into you in the hallway for the next 30 years, so be collegial.

  • Assistant Professors—Read the book Lab Dynamics: Management Skills for Scientists by Science's Next Wave columnists Carl M. Cohen and Suzanne L. Cohen. This is an extraordinarily useful tool which trains you to observe your own behavior and to anticipate the consequences of your behavior on your colleagues, employees, and students.

The Eyes Have It

It was in Lewontin’s lab, she says, that she became fascinated with color vision and butterflies. After reading about work that Jeremy Nathans and others had done on primates in the 1980s, Briscoe, with the assistance of Lewontin and co-advisor Naomi Pierce, developed a dissertation focus. “Color vision requires the presence of at least two color receptors, with different sensitivities to light,” Briscoe explains. “The proteins expressed by these receptors are different opsins, each combined with the same retinal-derived chromophore. They form the visual pigments that are found in the eyes of organisms. Nathans and others demonstrated that humans, chimps, and gorillas evolved red-green color vision via an opsin gene duplication event, so I wanted know if butterflies evolved red-green color vision through a similar genetic mechanism.”

Briscoe was the first person to clone six opsin genes from the Eastern Tiger Swallowtail ( Papilio glaucus), a papilionid butterfly, work she did during her Ph.D. research. As a postdoc at the University of Arizona, she continued the work by examining the pattern of opsin mRNA expression in swallowtail eyes using molecular biology techniques. Briscoe’s researchconfirmed that the red-sensitive opsin of swallowtail butterflies had evolved from a duplication of a green-sensitive opsin ancestor, and that this gene-duplication event had occurred after the divergence of the lineages leading to papilionid and nymphalid butterfly families. “This suggested to me that butterflies lacking this duplicate opsin gene may be red-green color blind,” she says. Since then, Guillermo Zaccardi, a visiting graduate student to Briscoe’s UC-Irvine lab, has used behavioral studies that Briscoe says proves the hypothesis. The work is not yet published.

Briscoe is also investigating how many times opsin gene duplications have occurred in butterflies, when they happened, and whether the evolution of opsins has led to new photoreceptor subtypes. For instance, a recent paper from her lab and the lab of Steven Reppert at the University of Massachusetts Medical School, Worcester, published in Neuron, showed that the monarch butterfly has a novel pattern of ultraviolet opsin expression in the polarization-sensitive dorsal rim area of the eye. Briscoe’s future work will explore whether this same pattern of opsin expression is found in butterflies that have evolved additional opsin genes.

Other work from Briscoe’s labhas shown a link between butterfly vision and wing color. “The same genes that are responsible for generating wing color pigments,” Briscoe says, “are very likely those that produce the highly variable filtering pigments of the eyes, which directly affect the part of the spectrum to which the butterfly may perceive color.” In other words, two closely related species of butterfly may exhibit different wing colors and see color differently. One group may see color in the red-green spectrum whereas the other may discriminate color in the blue-ultraviolet spectrum. These differences may subtly bias these insects to only take nectar from the flowers they can see, decreasing the competition for one kind of plant. One of Briscoe's graduate students is investigating this hypothesis in field studies.

Undergraduate Cindy Wang and doctoral students, Nélida Pohl and Marilou Sison-Mangus, at the field site.

A Darwinian Disciple

Charles Darwin and others studied the pattern of wing color in butterflies to help them understand evolution. Briscoe continues the tradition by using technology Darwin could only imagine. By studying the evolution of the sensory system in butterflies, Briscoe has shown how gene duplication produces color sensitivities that have an impact on an animal’s ability to interact with its environment. As a result of that work, “we can no longer assume what one butterfly is able to see in a garden is the same as what another butterfly is able to see.”

Robin Arnette is editor of MiSciNet.

Photo credits: Cheryl Himmelstein and Adriana Brisoe.

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