2022-11-15 by Khushi Goel

[Transcript] IndiaAsksWhy | Why Do Snakes Not Have Limbs?

[00:10] Both- “Hi Everyone”

U- I am Utsuka

J- I am Jigyasa

Both- And you are listening to IndiaAsksWhy.

U- A science podcast supported by IndiaBioScience

J: Where we do the research for you to get smarter.

U: Join us, as India becomes more curious,

Both: one question at a time!

[0:33] J: Utsuka and Jigyasa spotted a snake charmer on the streets. Utsuka was mesmerized by its dance. But they both realized that the dancing snake had no legs or arms. That made them wonder: “Why snakes don’t have limbs?” Listen to the episode as they explore the reasons why snakes must have lost limbs.

And in the interview segment, they talk with Dr. Megha Kumar, a scientist from CCMB who studies early forms of animals – embryos. Dr. Kumar talks about how researchers study snakes and other animals to answer questions about how their bodies develop.

[1:20] U: Look how the snake moves! It looks like it is standing and making waves in the air.

J: Even though it has no legs and arms, you say it's standing and dancing?

U: Yikes! You are right! I wonder why snakes do not have limbs.

[Research typing sound] [01:44] J: Evolution! The answer to why snakes don't have limbs lies in how the snakes have evolved! But, Utsuka beware! We are now entering uncertain territories.

U: Uncertain territories?

[02:00] J: Evolution involves the study of the past! Since we cannot time travel, we have limited evidence. That's why it's uncertain or debatable. Scientists have different ideas on why snakes don't have limbs. One of the ideas is that many many years ago there could have been snake ancestors that used to have limbs, but over time they have lost their limbs!

[02:30] U: Lost their limbs? What do you mean Jigyasa?

[02:34] J: Recent studies by evolution scientists have found that ancient snakes like pythons start developing legs when they are just embryos. And their experiments suggest that the genes which control leg development are mutated, and that's why snakes don't complete their leg development.

[02:54] U: Wait, wait, that was a lot of new information. First, let me recap- snakes are reptiles- so they also hatch from eggs.

[03:07] J: Yes! And here scientists studied snake babies much before they were even ready to hatch.

[03:16] U: Coooool! And you said genes are mutated? What does that mean?

J: Yes. Do you remember genes, Utsuka?

U: Yes! Genes are fragments of DNA that have specific functions in the cells of our body.

J: ..and do you remember mutations are small changes in the DNA of a living organism? Right?

U: Yes I remember!

[03:42] J: So these small changes can sometimes show as big changes in the body! Like it could cause an organ to not form correctly in the embryo. U: Then will the embryo be able to live?

[03:57] J: Probably not. But then there can also be times when the mutations don't show up as big changes in the body.

U: So you mean, a small change happens and no one will know it happened?

[04:14] J: Exactly. And let's say over many years of generations of some slithery snake ancestor family, these small secret changes kept happening. But the effects didn’t show up in the individuals from the younger generations. U: Okay, but then if there was no effect, then how did snakes lose their limbs?

[04:40] J: It could have happened that in one younger generation there were enough mutations that a big change finally showed up!

U: big change- meaning losing the limb? [04:54] J: Yes! The mutations finally affected the development of limbs in the snake's embryo. And now, in this younger generation, the snakes that hatched out of the eggs were completely limbless!

U: Woah! But wait, how did this snake then walk or move without limbs? How did it do its functions?

[05:20] J: That’s a good question. It might have seemed the most difficult thing at that moment. We don't know, because we can't time travel! But it could be possible that without the limbs, the snakes might have been able to hide better or bury better into the soil, or be able to find food sources in the places where other snakes might not have reached!

[05:47] U: You mean that they were better at some skills which set them apart from others?

J: Yes, exactly. The limblessness might have given them an advantage over the other snakes! This could mean, the limbless snakes might have survived better than others and reproduced more snake babies like themselves! And those limbless snake babies reproduced to make more limbless snakes!

[06:22] U: But Jigyasa, all of this talk is of the past. Since we can't go back in time, how do scientists know this is really true?

J: That's a very good question Utsuka. This is exactly why some scientists study present-day snake embryos. And they found some exciting information there.

U: Oooo! Tell me more!

[06:46] J: So, when a snake baby or embryo is just starting to form in the egg, several genes are contributing to the development of different features in the snake body. Now, in the snake cells, while it is developing in the egg, there is one gene that helps in the development of toes, and another helps in the development of bones of the leg, etc. And then there is also a regulator gene that controls these genes.

[07:21] U: So does it mean, leg development starts in the snake embryo? But then why does the snake not have legs?

[07:29] J: Yes, yes. I am getting there. So even though it begins the development of the leg, it isn't able to sustain that development. And that's why the leg development stops abruptly and the leg bones don't develop further.

[07:49] U: Ohhh! These were the Mutations that might have accumulated over time and generations. And now we see it as a big change- limbless snakes!

J: Bingo! That’s exactly what I was getting at. And to confirm this idea, another study went a step further. They placed this mutated regulator gene of the snake into the mouse embryo’s DNA. So this time the mouse had the mutated regulator gene, instead of its normal regulator gene. Can you guess what might have happened?

[08:29] U: Umm…did the mouse not develop legs at all?

J: Perfect! The mouse embryo showed a behavior similar to the snake embryo! Further proving the point that the regulator gene is important for the correct and sustained development of legs in snakes!

U: This is super fascinating! Jigyasa, Does this mean we can put the same regular in any animal and make them lose limbs?

J: I know the perfect person to answer your question! Let's ring Dr. Megha Kumar!

[09:05] J: It’s time to ask a scientist

[09:12] U: Welcome back everybody now we have Dr Megha Kumar, senior scientist at CCMB, Hyderabad. Among many other exciting things, she studies how animals, zebrafish embryos develop and how aeries during cell division causes embryos to develop defectively. So Jigyasa, let’s go ahead and ask our questions, Shall we?

[09:34] J: Yeah.. is it possible that if we put this regulator in other animals, let's say a whale, a cat, a dog or any other animal… is it possible that they will also not develop limbs?

[09:51] M: Yes, so if you look at an example by the type of animal you are talking about, we consider, say whales.. It doesn’t have limbs, right? It swims like fish in the water. So if you look at the embryo of a whale you’ll see a similar pattern just as a snake that the limb genes are present in the embryo but this regulatory element or this regulator is absent. And that’s why whales do not develop limbs. But if you look at a cat or a dog, they have fully formed limbs, right? The hind- and the forelimbs. So if you look at a dog or a cat embryo, yes, this regulator is present and this results in the formation of a limb. So if we take a snake regulator and put it in a cat embryo, yes you’ll see some sort of reduction in the formation of the entire limb. So the hindlimb and forelimb may not be entirely formed. Because this regulator is going to stop the activity. So evolution has not gone in a very linear or a straight manner. But what has happened is that multiple times during evolution, different animals have lost different sets of genes.

[11:11] U: And how do you know it is only this gene which is responsible for whatever you see in the embryo?

M: So what different scientists have done is tried to tinker and manipulate different genes to see what kind of effects they have on the embryo. So sometimes some genes can directly affect a process, sometimes there is a combination of genes that works.

[11:40] U: Why are you interested in asking such questions? Like what brings you to ask so many curious questions about embryos?

[11:49] M: So why am I interested in this field is because embryos are spectacular biological entities which are so dynamic and they change constantly, right? It starts with one fertilized cell where male and female cells fuse, the sperm and the oocyte. Then they have all the information spectrum inside them to form a complete individual, right? And how these cells start to divide, how do they know that they are neighbors to this cell and how do they know their orientation and how they form different structures. How do the cells communicate to each other?

[12:37] J: Did you always know that you always wanted to study this ?

M: So till high school, till class twelve, I liked all aspects of biology. But when I came to undergraduate, during my bachelors is when I studied developmental biology as a subject where you look at different embryos. So undergraduate is when I realized that this subject is very interesting and gave me a basic primer on how the embryo tends to develop over time and how different structures are formed. I realized that becoming a scientist will give me a full time, full day chance to look at the embryo to study, to do any kind of experimentation and ask questions that I am interested in. So that time I decided to pursue science as a career for research. During my PhD I started working with fish. And they are very nice, small 2-4 cm long fish, the zebrafish. And they are called zebrafish because they have stripes like the zebra animal does. So that’s why we named it zebrafish. And now we understand that more than 80-90% of the human gene is also present in the zebrafish. So most diseases that happen in humans can be checked in the zebrafish. So if you look at a zebrafish embryo, it is actually transparent. So you can see different structures forming in real time just by using a simple microscope. Because it is transparent. And at some point I am studying basic biology for the interest of my curiosity but also to understand what kind of defects happen in children when they are born with such problems. Then that gives you a clinical aspect of understanding how embryos develop and why babies have certain problems and defects when they are born. So only when we understand basic science, we will be able to take it to what kind of defects happen in human babies.

[14:53] J: This has been amazing and we really enjoyed that it is possible to see the transparent fish embryos in the microscope when they develop. So if somebody is as curious as you and is determined to ask similar kinds of curious questions, what advice would you like to give to our listeners in that context?

[15:15] M: I think find something that you really, really enjoy doing and you are passionate about. Those two things have to come that you need to be passionate about it consistently and enjoy what you are doing and choose a profession that makes you do these two things together. So you may not have to be a scientist to enjoy science, right? There are many other kinds of careers you can pursue after doing basic science also. But do choose a profession where you are really, really enjoying and you are passionate and that’s why you become something like Sachin Tendulkar of your field, okay? So you don’t have to be doing cricket to be Sachin Tendulkar. You can be Sachin in your comfort zone and that's the most important thing.

J&U: Thank you so much.

[16:15] J: Do you now understand why snakes don’t have limbs?

U: Yes! It’s a long story spanning millions of years. Research says that some snakes had a mutation in a very important gene that tells their body to develop limbs. And as we can see, these snakes without limbs not only survived but thrived. Eventually, all snakes of the present generation had this mutation and they continue to pass it on.

J: Exactly! How do scientists know that the mutation was only in this particular gene?

U: Scientists like Dr. Megha Kumar, study with model embryos to understand the roles of different genes in embryo development.

J: Yes! Dr Megha studies one such model embryo in her lab. While she enjoys pursuing her curious questions in the lab, she advises our listeners to find what brings them joy and then pursue it with all their passion!

[17:20] J: But listeners what we know about snake embryos and snake genes may change over time.

U: Who knows one of our listeners might study snakes and find out something about them that we never knew before!

[17:42] U: So that’s it for today.

J: If you want to know more about today’s scientist, we have linked his profile in the Show Notes!

U: If you have any questions that you want us to explore, shoot them away to Indiaakswhy@gmail.com

J: If you'd like to directly talk to us directly, then join the fun, join the fun on our Telegram Group. Link in the show notes.

U: For updates on IndiaAsksWhy, follow us on @IndiaAsksWhy on Twitter, and @India_AsksWhy on Instagram.

J: Shweata N. Hegde and Ruchi Manglunia are the hosts for the podcast.

U: Indulekha M.S. edited this episode.

J: And Khushi Goel transcribed it.

U: and we are funded by the indiabioscience’s second outreach grant.

J: Until next time! Till then, stay tuned and stay curious.