Research in four countries, including the Technion researcher, investigated the evolution of venomous teeth in snakes: the success of snakes in the world lies in developmental changes that led to the appearance of the bite teeth and the venom gland
The enormous success of the group of advanced snakes in the world lies in a series of changes that occurred during evolution, which changed the embryonic development process of the tooth ridge in the upper jaw and led to the appearance of the bite teeth and the venom gland. This is what 16 researchers from four different countries write in Nature, among them Dr. Ram Rashef from the Faculty of Biology at the Technion.
The group of snakes evolved from a group of lizards about 140 million years ago. Several processes characterize the development of the new group. One is the lengthening of the body in which the thoracic region "took over" and occupied most of the area of the body axis with the exception of the head and tail. Another event related to the process and which apparently occurred at the same time, is the process of losing limbs. At first the front limbs became smaller and smaller until they were completely lost including the limb girdle and at a later stage the hind limbs also became smaller and in certain species that include all advanced snakes these limbs disappeared completely including the limb girdle. In the group of snakes, you can find a hind limb girdle and no femur that is underdeveloped. These processes of losing limbs and lengthening the body probably occurred simultaneously with the occupation of underground living niches.
The loss of limbs left the task of capturing, holding and fixing the prey to the front part of the body, i.e. the mouth. At this stage, several dramatic changes related to this task are revealed. One is the release of a relatively large number of skull bones from their connection to the brain box. Thus, for example, a number of bones related to the structures of the upper jaw are connected by joints only to the brain box and can move relatively freely along the axis - forward, backward and even to the sides, which helps a lot in holding, transporting and moving the prey inside the mouth. Another example is the release of the quadrate bone (the bone that connects the bones of the skull to the bones of the lower jaw, which made it possible to create a wider opening of the pharynx in order to swallow whole and large prey.
In the strangler family, the prey is captured and killed by suffocation using the massive body muscles. In the advanced snake families there is great variability as to the method of capture and killing. In this context, we find for the first time in evolution the development of a special gland located in the back of the upper jaw and developing from a bud common to it and the back of the maxillary dental ridge (the dental ridge located in the anterior-external part of the upper jaw).
The article in "Nature" resolves a long debate among researchers regarding the origin and development of venomous teeth in the advanced group of snakes, that is, zamenians, vipers (including the rattlesnakes, of America), the pathans (the cobras and mambas and various sea snakes) and the seraphim (such as the Ein Gedi snake found in our country). In this work, the SHH gene that is expressed at the beginning of the process of tooth development was used. From the expression of this gene and from experiments done on the embryonic development of the Israeli land viper and the water snake that lives in our region, we learn that the venom teeth that appear in venomous snakes come from the back of the maxillary tooth ridge. This tooth ridge, which is in the gnat family, is uniform and bears teeth that are mostly equal in shape and size, splitting at an early stage in evolution (about 60 million years ago) into two tooth ridges that have been preserved in this way among the gnat family. These two tooth ridges develop during embryonic development from two separate and independent developmental centers along the upper jaw, one anterior and the other posterior. This separation in the developmental processes is a key evolutionary point in the development of the venom gland and venom teeth. Indeed, at this stage we find that a new gland appears which during embryonic development develops in close connection with the posterior tooth ridge.
From looking at the morphology of many species of the Zemani family we find great variation in the appearances of the back teeth and the gland starting from a gland that secretes relatively few active substances to glands that secrete many and complex venoms and from an anatomical picture in which the collecting tube of the gland opens near relatively short teeth to a complicated connection between the tube of the gland and the teeth of the promising venom The flow of the secretion through canals or closed tubes within elongated teeth with sharp ridges.
When we examine the families of venomous snakes (vipers and cobras) we find that the front maxillary tooth ridge disappears during evolution and the back ridge carrying the venom teeth "migrates" forward during embryonic development in relation to other skull structures so that at the end of the process (toward hatching) this tooth ridge is located in the front of the mouth. These groups significantly improved the structure of the venom teeth and the quality of the venoms produced in the gland.
These changes that occurred as a result of genetic changes in the control of the developmental process enabled the contemporary appearance of the sophisticated biting mechanisms and consequently the success of the group of advanced snakes in the world. At their peak, these changes include a flexible skull adapted to injecting venom and swallowing large prey whole and activated by a complicated muscle system, one of which is connected to the venom gland and adapted to injecting venom during the bite.
"The venom gland produces and secretes a series of active substances, enzymes, toxins and others designed to ensure efficient hunting of prey used for beneficial and efficient nutrition," says Dr. Reshef. "Unfortunately, the poisonous snakes also use this complicated and complex mechanism for defensive purposes, sometimes against us, and the results are well felt in Israel, especially lately."
14 תגובות
Hill:
Ok. There are many types of evolution cheats.
I didn't mean your kind.
point:
And one more thing.
When you say that you do not know how the research will lead to anything other than the facts that it discovers and do so without knowing what the facts that it will discover are, you are actually underestimating the importance of facts that you do not know about.
point,
Development of organs in animals is controlled by a series of ~13 genes called HOX. A unique thing about the HOX gene series is that each gene is activated according to its position in the DNA. That is, the genes are arranged in a certain order one after the other, and the first will be expressed in the head, the second will be expressed in the abdomen, the third will be expressed in the hind limbs and so on (I am simplifying things here, but This is the general principle.
Beyond the interest that exists in genes that work in such a coordinated way, we can suddenly understand where front limbs came from, for example, during evolution. It turns out that in order to create the front limbs, the posterior Hox genes are activated, not the front ones. The conclusion from this is that the hind limbs developed first of all during evolution, and then underwent duplication in the embryonic creation plan, and as a result of the duplication, the front limbs were created (but that the genes that control them are still the ones that controlled the creation of the hind limbs).
Understanding the hox series yields results every day in new experiments in embryology and developmental biology. Embryology, at the very least, is closely related to medicine and in the near future also to tissue engineering.
In short, out of small insights and junior research facts jump big studies and significant insights.
And if you already mentioned the police, it seems to me that such studies can be exempted due to lack of public interest. 🙂
In any case, I don't think that this debate is essential, but only about highlights of what is interesting science and what is boring science.
To Michael, I still find it difficult to see how such a study on a change in the direction of tooth development in certain snakes can lead to something beyond the facts that the study itself reveals, in the same way one can study each and every element in any living creature whatsoever. Such studies will not lead to anything beyond the facts of the study itself.
Extinction of a large and dominant species is certainly worthy of research because it seems to contradict the principle of evolution and therefore it is interesting. Development of one tooth or another. It's not interesting anymore.
Michael
I rule out the theory of evolution (because in my opinion it is statistically impossible)
But does not exclude the sacrifice of monkeys to dogs, mice and pigs.
Where does this generalization come from?
point:
I don't accept your opinion because the search in all directions continues at the same time and each field contributes to the other.
Take for example the subject of dinosaurs.
They don't know what destroyed them, but there are good reasons to believe that it was a meteorite. If we had not asked the question we would have had much less chance of discovering the evidence of the meteorite as well.
All in all, this is an investigation that is very similar to a police investigation, with the only difference being the time frames.
It turns out that this difference in time is seen by many as a qualitative difference instead of a quantitative difference.
This is also the reason why evolutionists are willing to accept genetic evidence of familial kinship between humans but reject it when it comes to familial kinship between humans and monkeys.
Simple, because evolution is driven by 2 principles. And the principle that determines how the teeth will develop is the principle of survival. And only if we had concrete knowledge about the environment in which the snake developed in each generation, then we would be able to learn something, but even that is not fundamental because the environment can be different.
point:
And why do you think the research will not yield a new principle?
If you think about the regular script of science - that of experiment-theory-experiment, etc. then the new theory is always created when the experiment disproves a certain idea in the previous theory.
The experiment, in the historical sciences, is a search for evidence from the past to see if they correspond to the principles of existing theories.
The obvious goal (which is important in itself) is to confirm or disprove the known theories, but during the research, more serendipitous discoveries can be made.
Michael, it seems to me that the goal and interest in science are the principles and not the technical details (these are their role only to confirm or disprove the principles).
Therefore, an investigation of a certain subject without it leading to some kind of understanding of a new principle, or an intensification of an existing principle, is not scientifically interesting.
And in addition (to what Michael wrote), and this is perhaps the main point. !!! The most amazing phenomenon in the scientific process is that, almost always, the results, consequences, conclusions and applications of the "technical" scientific discoveries are surprising, diverse and completely predictable in advance.
Therefore, no one (apart from Einstein) can determine in advance what is worth and what is not worth researching, where an important discovery will come from and where not. Hence the enormous importance of academic pluralism.
point:
Science is driven by the desire to understand things - including things that happened in the past.
This desire leads to all kinds of science - including the historical sciences that include evolution and cosmology.
Throw away this desire and you have thrown away all science.
Sometimes I wonder if all this genetic-evolutionary research will be interesting in 200 years. Life there will already be genetically engineered.
If we use the analogy of a hard disk on a computer running an operating system.
So investigating the history of the snake's teeth is equivalent to investigating the history of the information in different places on the hard disk (that is, investigating why the specific bits appear in a specific location). Because on the one hand it is clear that the information written on the harisk was not written randomly, but on the other hand it is also clear that if the information had been written in a different place it would not have mattered so much (obviously a slightly different history ended up with that).
In short, this whole investigation seems terribly technical to me.
Kudos to Dr. Reshef!