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Two-headed worms tell us something interesting about evolution

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Two-headed worms tell us something interesting about evolution

Ashley Pope: This is a 60-second Science American science, I’m Ashley Pap.

You could say so Guillermo Ponz is a scientific monster hunter – even though he thinks the term “monster” never encompassed his subjects.

Guillermo Ponz: So these are ordinary animals that have gone through various developmental processes that ended up building bodies that you don’t expect.

Pap: What this researcher from Madrid, Spain, actually loves are the amazingly amazing animals. After all, study two-headed worms.

Ponz: We have worms that are usually normal, for example, with one head and one tail, this is normal, but sometimes they can have two heads or two tails. And on the other hand – worms, which always have one head and many tails.

Pap: Officially he looks at forked ringworms, which means things like earthworms that came out of their larval stage with two heads, or spontaneously grew two tails, or … some other combination of mixed appendages.

We know that some species, like some salamanders and insects, have the ability to grow appendages at the right time. But there is one type of ringworm that can re-grow unlike anything else we have ever seen in the kingdom.

Their segmented bodies, like earthworms with rows of ringed compartments, help them easily grow a new head or tail at the first sign of trouble.

Or even crazier, they can restore a whole new right side of their body if you cut it in half.

Ponz: … worms that do such crazy things that are very weird, very, you know, very, very weird things that these worms shouldn’t do, quote-don’t quote.

Pap: Once Ponz began to study the anatomically dangerous distances these worms traveled to grow and survive, he was fully involved.

And he realized that he and his team were not the first to get carried away. Ponz discovered that during the 18th and 19th centuries there was a golden age of research on “ugly creatures”.

Ponz: … 100-year-old literature will refer to the feelings of monsters, creatures, or monsters, or quirks, or, you know, they, all these variations that describe them. And after all, these animals are not monsters.

Pap: Fixation with a “resuscitated monster” makes sense, especially then. Mary Shelley’s novel “Frankenstein” was published in 1818, and it only heightened interest, and part of that interest turned into real research.

Ponz and a group of international researchers conducted an extensive review of existing knowledge about monster worms. They delved into 275 years of research – searching the journals of scientists’ observations, reading historical texts and even turning to the general scientific community to find out if anyone knew anything about the records of abnormal worms.

They wanted to understand all the different types and patterns of bifurcation and see if there are any clues as to how the oddities developed.

Their search led them to the jackpot of both history and science.

They came across documents and drawings of bifurcated worms from all over the world – in Latin, French and German, up to Russian, Japanese and even Indonesian. In all, they spent more than a year working on archives, translating old texts and following in the footsteps of monster worms.

They learned that bifurcation in worms was observed in more than 60 species of ringworm worms, and in some species up to 20% of the young were eventually bifurcated. This work was recently published in the journal Biological Reviews. [Guillermo Ponz-Segrelles et al., Monsters reveal patterns: bifurcated annelids and their implications for the study of development and evolution]

Ponz: That is, for example, in the case of a bifurcation, that when an animal is cut and regenerates, such as a tail, there must be some mechanism that determines where that tail will be, how it will be oriented, what’s behind, what’s front, what’s left, that right, that back, that ventral. And these mechanisms can be disrupted. And this can lead to different anatomies.

And it gives us clues as to what is important during this process. Of course, these are childish steps. So we just point to this process, it’s a phenomenon, we say, okay, hello, it’s happening, there are these animals doing such amazing things. We must not forget about them, let us consider them.

Pap: They also realized that there is a strong correlation between the type of bifurcation and the development of internal organs. This means that the method of separating the worms reliably indicates when additional sets of organs are present.

With this information, Ponz and his team were able to essentially draw up a plan, or instructions, for the reliable and reusable creation of bifurcated worms … which is potentially a very useful resource for scientists interested in studying developmental mechanisms.

This long-forgotten study of worm developmental abnormalities seems ready to return. According to Ponzo, this information can go far beyond ringed and even insects to help us better understand how things like growth and development … both ordinary and monster, actually happen.

Ponz: In a sense, we are now following this trend that they started then, studying these animals to try to understand larger-scale pictures of nature. Usually development leads to a certain way of approving them to a certain point. So you have a development that ends in a more or less preserved anatomy. But sometimes this is not the case. And it can teach us for some reason about development processes. And it’s interesting.

Pap: For the 60-second Scientific American Science I am Ashley Pap.

[The above text is a transcript of this podcast.]

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