For deer mice living in the Nebraska Sandhills, color can literally be the difference between life and death.
When they first colonized the region, the dark-coated mice stood out starkly against the light-colored, sandy soil, making them easy prey for predators. Over the next 8,000 years, however, the mice evolved a new system of camouflage – lighter coats, changes in the stripe on their tails and changes in the extent of pigment across their body – that allowed them to blend into their new habitat.
Now Harvard researchers are using their example to answer one of the fundamental questions about evolution - is it a process marked by large leaps – single mutations that result in dramatic change in an organism – or is it the result of many smaller changes that accumulate over time?
As described in a March 15 paper in Science, a team of researchers, including former Postdoctoral Fellow Catherine Linnen, now an Assistant Professor at the University of Kentucky, and led by Professor of Organismic and Evolutionary Biology and Molecular and Cellular Biology Hopi Hoekstra, were able to show that the changes in mouse coat color were the result not of a single mutation, but at least nine separate mutations all within a single gene.
"The findings demonstrate how the cumulative effect of natural selection, acting on many small genetic changes, can produce rapid and dramatic change," Linnen, the first author of the paper, said. "This helps us to understand, from a genetic perspective, the uncanny fit between so many organisms and their environments—by acting on many small changes, rather than a handful of large ones, natural selection can produce very finely honed adaptations."
Surprisingly, Hoekstra said, that honing occurred in a single gene.
The role of this gene, called agouti, in camouflage was first discovered by Linnen, Hoekstra and colleagues in 2009, and it is responsible for changes in pigmentation in the coats of many animals. Every domesticated black cat, for example, has a DNA deletion in the gene.
What surprised Hoekstra and her team, however, wasn't that the gene was involved, but that each of the nine mutations were tied to a unique change in the animal's coats, that all the new mutations led to more camouflaging color, and that the mutations occurred in a relatively short, 8,000-year timeframe.
"Essentially, it seems as though these mutations – each of which makes the mouse a little lighter and more camouflaged – have accumulated over time," Hoekstra said.
Focusing on these mutations, researchers then examined the DNA of natural populations of the mice to determine whether the mutations are actually beneficial.
"For each of the mutations associated with color change, we also find a signal that's consistent with positive selection," Hoekstra said. "That implies that each of the specific changes to pigmentation is beneficial. This is consistent with the story we are telling – about how these mutations are fine-tuning this trait."
While the findings offer valuable insight into the way natural selection operates, Hoekstra said they also highlight the importance of following research questions to their ultimate end.
"The question has always been whether evolution is dominated by these big leaps or smaller steps," she said. "When we first implicated the agouti gene, we could have stopped there and concluded that evolution takes these big steps as only one major gene was involved, but that would have been wrong. When we looked more closely, within this gene, we found that even within this single locus, there are, in fact, many small steps."
Going forward, Hoekstra said, her team hopes to understand the order in which the mutations happened, which would allow them to reconstruct how the mice changed over time.
"For evolutionary biologists, this is exciting because we want to learn about the past, but we only have data from the present to study it," she said. "This ability to go back in time and reconstruct an evolutionary path is very exciting, and I think this data set is uniquely suited for this type of time travel."
Taking the time to understand not only which genes are involved, but which specific mutations may be driving natural selection, Hoekstra said, can give researchers a much fuller picture of not only the molecular mechanisms by which mutations alter traits, but also the evolutionary history of an organism as well.
"By doing this we've discovered all kinds of new things," she said. "While we often think about changes happening in the entire genome, our results suggest that even within a very basic unit – the gene – we can see evidence for evolutionary fine-tuning."
Peter Reuell | EurekAlert!
Designer cells: artificial enzyme can activate a gene switch
22.05.2018 | Universität Basel
Flow of cerebrospinal fluid regulates neural stem cell division
22.05.2018 | Helmholtz Zentrum München - Deutsches Forschungszentrum für Gesundheit und Umwelt
At the LASYS 2018, from June 5th to 7th, the Laser Zentrum Hannover e.V. (LZH) will be showcasing processes for the laser material processing of tomorrow in hall 4 at stand 4E75. With blown bomb shells the LZH will present first results of a research project on civil security.
At this year's LASYS, the LZH will exhibit light-based processes such as cutting, welding, ablation and structuring as well as additive manufacturing for...
There are videos on the internet that can make one marvel at technology. For example, a smartphone is casually bent around the arm or a thin-film display is rolled in all directions and with almost every diameter. From the user's point of view, this looks fantastic. From a professional point of view, however, the question arises: Is that already possible?
At Display Week 2018, scientists from the Fraunhofer Institute for Applied Polymer Research IAP will be demonstrating today’s technological possibilities and...
So-called quantum many-body scars allow quantum systems to stay out of equilibrium much longer, explaining experiment | Study published in Nature Physics
Recently, researchers from Harvard and MIT succeeded in trapping a record 53 atoms and individually controlling their quantum state, realizing what is called a...
The historic first detection of gravitational waves from colliding black holes far outside our galaxy opened a new window to understanding the universe. A...
A team led by Austrian experimental physicist Rainer Blatt has succeeded in characterizing the quantum entanglement of two spatially separated atoms by observing their light emission. This fundamental demonstration could lead to the development of highly sensitive optical gradiometers for the precise measurement of the gravitational field or the earth's magnetic field.
The age of quantum technology has long been heralded. Decades of research into the quantum world have led to the development of methods that make it possible...
02.05.2018 | Event News
13.04.2018 | Event News
12.04.2018 | Event News
22.05.2018 | Life Sciences
22.05.2018 | Earth Sciences
22.05.2018 | Trade Fair News