The duck is one of the strangest animals on earth. It has a beak similar to that of a duck, but its body is completely covered with fur. It yields milk, but without teats. And as if to complicate the matter even more, he does not give birth to offspring but lays eggs
When European naturalists first saw the duck's stuffed corpse, they thought it was a bad joke. Their first thought was that someone had sewn a duck beak to the body of a full-grown beaver. Hard to blame them, as the duck is one of the strangest animals on earth. It has a beak similar to that of a duck, but its body is completely covered with fur. It yields milk, but without teats. And as if to complicate the matter even more, he does not give birth to offspring but lays eggs. In short, it is a mix and match of features that we are used to seeing in birds, reptiles and mammals - but not all together.
In recent years, scientists from around the world have gathered with the aim of deciphering the duck's genome, and to understand how its unusual features are related to its DNA. An analysis of the genome was published Tuesday (May 8) in the scientific journal Nature, and it may help scientists reach a more complete understanding of the evolution of all mammals, including humans. The duck itself is classified as a mammal, as it is covered in fur and produces milk.
"The fascinating mix of traits in the duck genome provides many clues to the evolution and way mammalian genomes work," says Dr. Richard K. Wilson, director of the Genome Center at the University of Washington and lead author of the paper. "By comparing the duck's genome to the genomes of other mammals, we can study genes that have been conserved during evolution."
The duck represents one of the first buds of the mammal line, which began its existence about 166 million years ago. It is one of the earliest primitive mammalian ancestors, and while later mammals have lost their reptilian features, the duck still faithfully represents the ancient lineage from which it descended.
The article in Nature analyzes the genome sequence of a duck named Glennie, from New South Wales, Australia. The project was funded in large part by the National Human Genome Research Institute, which belongs to the National Institutes of Health in the USA. The authors of the study came from the United States, Australia, England, Germany, Japan, New Zealand, Spain and of course - also from Israel, in the person of Professor Doron Lantz from the Weizmann Institute of Science.
"At first glance, the duck appears to be the product of an evolutionary accident," says Dr. Francis S. Collins, director of the National Human Genome Research Institute. "But despite its strange shape, its genome sequence is invaluable, and it will allow us to understand how biological processes evolved in mammals."
"While we've always been able to compare and weigh these creatures based on their physical attributes, internal anatomy and behavior, it's really amazing to be able to compare their 'creature plans,' and look closely at how evolution brings about change," says Wilson.
As part of the analysis, the researchers compared the duck genome with the genomes of a human, mouse, dog, opossum (marsupial) and chicken. The chicken was chosen as a representative of the egg-layers, which also include long-extinct reptiles, but much of whose DNA was transferred to the duck and other mammals during evolution.
One of the most important developments in the transition from reptiles to mammals was the transition from laying eggs to giving birth to milk-sucking animals. Eggs contain many nutrients that allow the fetus inside to grow. Mammals, on the other hand, nourish the fetus inside the body, through the placenta, and after birth they nurse it with rich milk. The evolution that the ancient reptiles went through to the mammals we know today must have been long and tortuous, and the duck is a kind of 'living fossil' that reveals to us one of the stages of this transition. The researchers discovered that the duck's DNA reflects this position. It contains all the genes necessary to make casein - an important protein in milk. On the other hand, the vitellogenin genes, which make up the yolk in the egg, are in the process of reduction - there is only one copy of the vitellogenin gene in the duck, while there are three copies in the chicken. In other words, first the ability to produce milk developed, and only then did the reptile's egg-laying system begin to degenerate.
The researchers also tried to determine which of the duck's features are related to reptiles at the DNA level. The male ducks are armed with spurs on their hind legs, with which they are able to inject a dose of poison strong enough to kill a dog. When the scientists analyzed the genetic sequences responsible for producing the poison in the male duck, they discovered that these genes evolved from a gene called defensin, which originally coded for an antimicrobial protein. The gene coding for the poison of various reptiles also evolved from the defensin gene, but in a different way. It is evident that this case is a beautiful example of convergent evolution in different organisms.
In Israel, Professor Doron Lantz and Dr. Tzvia Olander from the Weizmann Institute joined the research, who reviewed the genome and looked for clues to the duck's sensory system. They discovered that, like many mammals and reptiles, the duck is endowed with two parallel olfactory systems. The second system, called the vomeronasal system, does not exist in humans, and enables the sensing of solid and liquid substances that are not airborne. This system has a certain similarity to the sensory system of the tongue. For example, it allows snakes, which send their tongues to the ground in front of them, to feel the tracks of their prey in the dirt. The duck is well adapted to its underwater environment, where it spends most of its life. He closes his eyes and ears when he swims, but he is apparently able to locate, with the help of the vomeronasal system, 'smells' even underwater. The importance of this parallel organ is evidenced by the fact that while most mammals do not have more than a hundred or two hundred vomeronasal olfactory receptors, the duck has about a thousand such receptors, which may allow it to track underwater prey as if it were a hunting dog.
Perhaps the most surprising discovery of the study was that the duck has no less than ten sex chromosomes. As a comparison, humans have only two sex chromosomes - X and Y. The duck's sex chromosomes are very different from those of other mammals, and in fact there is no similarity between our sex chromosomes and the duck's sex chromosomes. The only duck chromosome that resembles our X chromosome is autosome number 6, which is not a sex chromosome. This finding corresponds to the theory that has been proposed for a long time, according to which the sex chromosomes of mammals evolved from normal chromosomes - autosomes - of reptiles.
It is hard to believe that the early naturalist who sent the first stuffed duck carcass to Europe imagined in his mind that it would have such great importance. Sequencing and analyzing the duck genome yielded many insights that shed new light on the evolutionary processes that occurred during the transition from reptiles to mammals 166 million years ago. These insights help us to better understand where we came from and the changes we went through on the long road from the snake to man.
Thanks to Professor Doron Lantz from the Weizmann Institute for his help and advice. (For the center's knowledge, Prof. Lantz's articles)
For information on the website of Washington University in St. Louis
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to Arya Seter
The term "primitive" in its scientific context means - ancient. while in its social context
Its meaning is retarded. Therefore, since we are dealing with scientific matters, the use of the term primitive=ancient is absolutely correct since it comes to indicate the evolutionary stage that that animal represents. For example, you may remember from mathematics that the integral of a function is also called a "primitive".
Therefore, on behalf of the other ducks, I respectfully apologize and confirm the wording that appears in the article.
lion:
After all, because of the possibility you described in your last response (which is the one supported by the fossil findings) I wrote my words and because of the possibility that you may not have meant that the marsupials were on the way between the lamb and its young, I only wrote that your words imply that this is the case and that this is not exactly your claim.
Michael
When I pointed out a similarity or gradation in the stages, it was not to claim that the marsupials are a step on the way to the placental mammals. They can of course be separate branches from the beginning in the evolutionary tree and it is possible, just for example, that the marsupials evolved from mammals that were more similar to the placental mammals. You never know - until you base it on genome research.
For example, it is known that the lungs and the swim bladder are homologous organs. It is trivial to think, and so did Darwin, that the lungs developed from the swim bladder, while the opposite is true...
lion:
From what you say, it sounds as if marsupials are an evolutionary stage on the way between egg-laying and brood-bearing.
This is not the prevailing opinion today as can be seen here:
http://en.wikipedia.org/wiki/Marsupialia
To complete the picture on the classification of mammals and the duck. The department of mammals is divided into three sub-departments (or whatever it's called): 1. The placental mammals (because their fetus is wrapped in the placenta) - which is us and most of the other mammals we know. 2. The marsupials - the kangaroo, the koala and the other Australian marsupials as well as the opossums from the American continent. 3. The bib mammals - the duck and the ant hedgehog. They are called bib mammals because they have a common opening for secretions and sex - like reptiles and birds. As mentioned, bib mammals do not have nipples. The mother produces milk in glands scattered on her ventral skin and the pup simply licks her belly. It is easy to understand how evolutionary development led to the concentration of these glands in defined areas and the formation of nipples. With pouch mammals, the pup comes out when it is actually a tiny fetus that stays in the pouch and suckles there. There is a certain sequence between egg laying and littering. Some lay eggs, some the embryo half comes out and half stays inside and suckles (marsupials) some hatch and suckle and there are fish that spawn fry - the eggs hatch inside.
Do not call a duck a primitive mammal (or other creatures - primitive), this is just human chauvinism. Every creature we know has developed in its own way and is adapted to its environment and succeeds in it.