When black mice first invaded the sandhills of Nebraska they contrasted with the light colors of the sand, making them easy prey. Over the next 8,000 years the mice developed camouflage systems, brighter colors, changes in tail stripes, and changes in pigments that allowed them to blend in with the landscape.
For the deer mice living in the sandhills of Nebraska, color can mean the difference between life and death.
When black mice first invaded the area they contrasted with the light colors of the sand, which made them easy prey. Over the next 8,000 years the mice developed camouflage systems, brighter colors, changes in tail stripes, and changes in pigments that allowed them to blend in with the landscape.
Now researchers at Harvard University are using their example to answer fundamental questions about evolution. Is it a process that requires big leaps - a single mutation that manifests itself in a dramatic change in the living creature itself - or the result of many small changes that accumulate over time?
In an article published on March 15 in the journal Science, a team of researchers, including one who was a postdoctoral fellow at Howard, Kathryn Leinen, then a professor at the University of Kentucky, and Hopi Haekstra, a professor of organismal and evolutionary biology and molecular and cellular biology, were able to show that the changes in the colors of the mouse's fur are not The result of a single mutation but a sequence of at least nine mutations in the same gene.
The findings demonstrate how the cumulative effect of natural selection, acting on many small gene changes, can produce rapid and dramatic changes." says Leinen. This helps us to understand from the genetic point of view the good compatibility between many creatures and the environment in which they live. By acting on many small changes, rather than on perceived large changes, natural selection can produce the most subtle and finely tuned adaptations."
Whereas Huekstra says that surprisingly this delicacy happened in one garden.
The role of this gene, known as agouti, in camouflage was first discovered by the two and their colleagues in 2009, and is responsible for changes in pigmentation in the fur of many animals. Every black domestic cat, for example, lacks this gene in its DNA.
What surprised the researchers and their staff was not that this gene was involved in determining the color, but that each of the nine mutations were associated with unique changes in the animal's fur, and that all the new mutations led to more camouflage colors, and that the mutations were created in the last 8,000 years."
"These mutations, each of which made the mouse slightly brighter and better camouflaged, appear to have accumulated over time," Hoekstra said. Focusing on these mutations, the researchers examined the DNA in natural mouse populations to determine whether these mutations are indeed beneficial."
"For each of the mutations associated with the changes in the deer, we found signals that this is a positive selection," Hoekstra said. "The implication is that each of the specific changes in pigmentation was beneficial and this strengthens our explanation of how the mutations enable fine-tuning of a trait."
While the findings provide valuable insight into the mechanism of the natural selection process, the two want to emphasize the importance of follow-up studies to answer important questions: "We have always asked whether ovulation is controlled by big jumps or small steps," Hoekstra said. "When we first examined the agouti gene, we could have stopped and concluded that evolution had taken a big step and that only one gene was involved in the process, but that was a wrong conclusion. When we examined the issue closely, inside the garden, we found that even within one site, there were many small changes."
She hopes to understand in depth the order in which the mutations occurred, in order to reproduce the stages of change in this mouse species. "For evolutionary biologists, this is exciting because we want to learn about the past, but we only have data from the present to study." saying. "The ability to go back in time and reconstruct an evolutionary trajectory is fascinating, and I believe that this data series would be suitable for this type of time travel."
According to Hoekstra, taking the time to understand not only which genes are involved in the process but also which specific mutations drive natural selection can provide researchers with a more complete picture of not only the molecular mechanisms by which mutations change traits, but also the evolutionary history of the creature. "When we did this we discovered not only a variety of new things" she said. "While the common thought is to examine changes occurring in the entire genome, our results show that even within the most basic unit - the gene - we see evidence of evolutionary refinement."
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There are issues of lack of information in this article:
1. 8,000 years may be a short time for species whose number of offspring is small and their reproduction rate is slow, but mice become active from the age of two months and can produce 5-8 offspring every 26 days for about 3 years. This is one reason why they are used for research.
2. One genetic mutation may have changed the color of the fur to something other than black, but certainly not all nine mutations were effective but only some of them. According to the description in the article, it seems as if the researchers are actually saying that they know the order in which the mutations appeared and that they appeared in such a way that mutations that would not have been effective if they had appeared first, actually appeared at a later stage where their combination optimized the effective mutations and therefore all mutations are effective. The problem is that this is an assumption from the context and not what was said in it.
3. Black is indeed an effective color - at night, against many predators. In addition, the mouse must have survived there too because apart from color, it has other survival skills. In fact, without additional qualifications, he probably would not have reached a critical mass sufficient to create the expression of genetic changes. In order for a mutation to manifest, a biosphere/niche stable enough to contain many different individuals that will produce offspring is needed. The increase in the population with the color similar to the environment makes sense because in this environment, the aforementioned color gives a defensive advantage from crazies.
And yet the article claims they were easy prey because of the black color. which contradicts the ability for sufficient stability. (Although, as I mentioned at the beginning, mice reproduce quickly and put many generations in 8000 years).
For anyone who claimed that there is no connection between evolution and genetics