The evolution of Dark-flyFebruary 04, 2016
On November 11, 1954, Syuiti Mori turned out the lights on a small group of fruit flies. More than sixty years later, the descendents of those flies have adapted to life without light. These flies--a variety now known as "Dark-fly"--outcompete their light-loving cousins when they live together in constant darkness, according to research reported in the February issue of G3: Genes|Genomes|Genetics. This competitive difference allowed the researchers to re-play the evolution of Dark-fly and identify the genomic regions that contribute to its success in the dark.
"We hope understanding the genetics behind Dark-fly's adaptations will shed light on how genes are selected during rapid evolution," says study leader Naoyuki Fuse of Kyoto University. The Dark-fly project is the longest-running example of an experimental evolution study where scientists follow a population over many generations. It is also the first to analyze genome evolution in a multicellular organism adapted to a defined condition in the lab.
The project was initiated by Mori as part of a series of experiments investigating how the traits of fruit flies are altered in response to changes in their environment. The fruit fly Drosophila melanogaster is a heavily studied model organism often used to examine genetic changes during evolution. To keep the flies away from light, they are reared in vials kept in a large pot painted black on the inside and covered with a blackout cloth. When the vials and food need to be changed, the researchers tend to the flies in the pitch dark, then use a feeble red light to check on their work. Fruit flies can't see this light because the species lacks those light receptor proteins that absorb red wavelengths.
When Mori retired, he passed on the precious fly stocks to his colleagues at Kyoto University, who have maintained them continuously to this day. The stock of flies has now spent more than 1,500 generations without light. In human terms, that would be like sequestering generations of our ancestors in the dark for 30,000 years.
Today, Dark-fly looks almost identical to normal (wild-type) D. melanogaster, but the variety is also subtly different. For example, Dark-fly individuals move around more in response to sudden light exposure, even after spending a generation in normal day/night cycles. They are also more sensitive to certain smells and have longer head bristles, which are sensory organs that serve as the fruit fly version of a cat's whiskers. Dark-fly also produces more offspring when kept in constant darkness than in alternating light and dark.
But although Dark-fly does better in the dark than the light, is it more highly adapted than the wild-type to its dim environment? The team tested this hypothesis by housing the two types of fruit flies together, allowing them to mate at random, and then assessing the parentage of the flies that made up the next generations. The results showed that Dark-fly has a competitive advantage in reproduction over the wild-type when bred in the dark. Fuse suggests this might be due to differences in pheromone signaling when the flies select their mates, or to altered circadian rhythms of mating or sleep behaviors.
Which genes are responsible for the adaptation to dark conditions? Previously, the team sequenced the Dark-fly genome, identifying mutations that distinguish it from wild-type. But not many of those genetic variants are likely to be responsible for the adaptations that help Dark-fly thrive without light; many of the variants may have no effect, or may affect unrelated traits. To hone in on the dark-adaptation genes, the team performed another kind of experimental evolution study.
They first reared Dark-flies and normal flies in mixed colonies, allowing the two types to interbreed freely for 49 generations. These colonies were maintained in constant dark and compared to control colonies with normal 24-hour light/dark cycles. With each generation, those flies that produced the most offspring contributed more of their genes to the colony as a whole. As the genomes of the two types of fly mixed, those genes responsible for Dark-fly's unique adaptations should become more common in the colony kept in the dark. To find those genes, the team sequenced the genomes of flies at the beginning and end of the experiment and looked for genetic variants originating in Dark-fly that became more common only under the dark conditions.
Such variants were located in 28 regions of the Dark-fly genome. From these regions, the researchers narrowed down the candidates to 84 genes. Among these candidates are likely the genes associated with dark-adaptive traits. These include genes that encode chemical receptors, and genes involved in pheromone synthesis, the formation of smell memories, and circadian rhythms. In future work, the team will examine the activity and functions of these candidates to link them to specific Dark-fly adaptations.
"We will soon have the ability to try my dream experiment: using genome-editing technology to introduce defined mutations into the wild-type to try to reproduce the Dark-fly's traits. This would give us a precise molecular profile of this remarkable example of evolution in the lab," says Fuse.
Dynamics of Dark-Fly Genome Under Environmental Selections
Minako Izutsu, Atsushi Toyoda, Asao Fujiyama, Kiyokazu Agata, and Naoyuki Fuse
G3: Genes|Genomes|Genetics February 2016 6: 365-376; doi:10.1534/g3.115.023549
This work was supported by GCOE program of Kyoto University, NIG Collaborative Research Program, and Japan Society for the Promotion of Science grants.
About the Genetics Society of America (GSA)
Founded in 1931, the Genetics Society of America (GSA) is the professional scientific society for genetics researchers and educators. The Society's more than 5,000 members worldwide work to deepen our understanding of the living world by advancing the field of genetics, from the molecular to the population level. GSA promotes research and fosters communication through a number of GSA-sponsored conferences including regular meetings that focus on particular model organisms. GSA publishes two peer-reviewed, peer-edited scholarly journals:GENETICS, which has published high quality original research across the breadth of the field since 1916, and G3: Genes|Genomes|Genetics, an open-access journal launched in 2011 to disseminate high quality foundational research in genetics and genomics. The Society also has a deep commitment to education and fostering the next generation of scholars in the field. For more information about GSA, please visit http://www.genetics-gsa.org.
Genetics Society of America
Related Evolution Articles:
The evolution of cells and organisms is thought to have been preceded by a phase in which informational molecules like DNA could be replicated selectively.
A new study by University of Arizona biologists helps explain why different groups of animals differ dramatically in their number of species, and how this is related to differences in their body forms and ways of life.
A genome project, comprising six evolutionary biologists from Professor Axel Meyer's research team from Konstanz and researchers from China and Singapore, sequenced and analyzed the genome of the tiger tail seahorse.
Rapid evolution of other species happens all around us all the time -- and many of the most extreme examples are associated with human influences.
Landscapes are formed by a combination of uplift and erosion.
How enzymes -- the biological proteins that act as catalysts and help complex reactions occur -- are 'tuned' to work at a particular temperature is described in new research from groups in New Zealand and the UK, including the University of Bristol.
On Nov. 11, 1954, Syuiti Mori turned out the lights on a small group of fruit flies.
A team of researchers, among them a zoologist from the University of Cologne, has succeeded in reconstructing a 160 million year old compound eye of a fossil crustacean found in southeastern France visible.
Evolution may be more intelligent than we thought, according to a University of Southampton professor.
Organized opposition to the teaching of evolution in public schoolsin the United States began in the 1920s, leading to the famous Scopes Monkey trial.
Related Evolution Reading:
Why Evolution Is True
by Jerry A. Coyne (Author)
"Coyne's knowledge of evolutionary biology is prodigious, his deployment of it as masterful as his touch is light." -Richard Dawkins
In the current debate about creationism and intelligent design, there is an element of the controversy that is rarely mentioned-the evidence. Yet the proof of evolution by natural selection is vast, varied, and magnificent. In this succinct and accessible summary of the facts supporting the theory of natural selection, Jerry A. Coyne dispels common misunderstandings and fears about evolution and clearly confirms the scientific truth that... View Details
Evolution: The Cutting-Edge Guide to Breaking Down Mental Walls and Building the Body You've Always Wanted
by Joe Manganiello (Author)
Joe Manganiello first gained recognition around the world for his incredible, sculpted body while winning both popular and critical praise as the star of HBO's True Blood. Now, from the man that Magic Mike director Steven Soderbergh called “walking CGI,” comes the cutting-edge guide to achieving the perfect body and therefore enhancing your overall quality of life.
With a build that men envy and women adore, Joe Manganiello is more than qualified to write the end-all guide to sculpting the perfect body. His fit physique catapulted him to the top of the list of... View Details
Evolution: A Visual Record
by Robert Clark (Author)
Stunning images to reawaken us to the scientific process that drives the amazing diversity of life on earth
Evidence of evolution is everywhere. Through 200 revelatory images, award-winning photographer Robert Clark makes one of the most important foundations of science clear and exciting to everyone. Evolution: A Visual Record transports readers from the near-mystical(human ancestors) to the historic (the famous 'finches' Darwin collected on the Galapagos Islands that spurred his theory); the recently understood (the link between dinosaurs and modern birds)... View Details
by Douglas J. Futuyma (Author), Mark Kirkpatrick (Author)
Extensively rewritten and reorganized, this new edition of Evolution--featuring a new coauthor: Mark Kirkpatrick (The University of Texas at Austin)--offers additional expertise in evolutionary genetics and genomics, the fastest-developing area of evolutionary biology. Directed toward an undergraduate audience, the text emphasizes the interplay between theory and empirical tests of hypotheses, thus acquainting students with the process of science. It addresses major themes--including the history of evolution, evolutionary processes, adaptation, and evolution as an explanatory... View Details
Evolution: Still a Theory in Crisis
by Michael Denton (Author)
More than thirty years after his landmark book Evolution: A Theory in Crisis (1985), biologist Michael Denton revisits his earlier thesis about the inability of Darwinian evolution to explain the history of life. He argues that there remains “an irresistible consilience of evidence for rejecting Darwinian cumulative selection as the major driving force of evolution.” From the origin of life to the origin of human language, the great divisions in the natural order are still as profound as ever, and they are still unsupported by the series of adaptive transitional forms predicted by... View Details
Improbable Destinies: Fate, Chance, and the Future of Evolution
by Jonathan B. Losos (Author)
A major new book overturning our assumptions about how evolution works
Earth’s natural history is full of fascinating instances of convergence: phenomena like eyes and wings and tree-climbing lizards that have evolved independently, multiple times. But evolutionary biologists also point out many examples of contingency, cases where the tiniest change—a random mutation or an ancient butterfly sneeze—caused evolution to take a completely different course. What role does each force really play in the constantly changing natural world? Are the plants and animals that... View Details
Evolution: Making Sense of Life
by Carl Zimmer (Author), Douglas J. Emlen (Author)
Dr. Gundry's Diet Evolution: Turn Off the Genes That Are Killing You and Your Waistline
by Steven R. Gundry (Author)
"Dr. Gundry has crafted a wise program with a powerful track record.â
âMehmet Oz, M.D., professor and vice chair of surgery, NY Presbyterian/Columbia Medical Center
Does losing weight and staying healthy feel like a battle? Well, itâs really a war. Your enemies are your own genes, backed by millions of years of evolution, and the only way to win is to outsmart them. Dr. Steven Gundryâs revolutionary book shares the health secrets other doctors wonât tell you:
â¢ Why plants are âgoodâ for you because theyâre âbadâ for you,... View Details
Evolution: How We and All Living Things Came to Be
by Daniel Loxton (Author), Daniel Loxton (Illustrator)
Evolution is the process that created the terrible teeth of Tyrannosaurus rex and the complex human brain, clever enough to understand the workings of nature. Young readers will learn how a British naturalist named Charles Darwin studied nature and developed his now-famous concepts of natural selection and survival of the fittest. And how modern-day science has added to our understanding of the theory of evolution. Can something as complex and wondrous as the natural world be explained by a simple theory? The answer is yes, and now Evolution explains how in a way that makes it easy to... View Details
Evolution: The Human Story
by DK (Author)
How did we develop from simple animals inhabiting small pockets of forest in Africa to the dominant species on Earth? Traveling back almost eight million years to our earliest primate relatives, Evolution: The Human Story charts the development of our species from tree-dwelling primates to modern humans.
Investigating each of our ancestors in detail and in context, from the anatomy of their bones to the environment they lived in, Evolution: The Human Story profiles every human relative and ancestor discovered to date, and illustrates them in lifelike form.
Amazingly... View Details