A new world of tiny predators

A new world of tiny predators

Researchers have discovered a previously unknown supergroup of rare single-celled creatures with healthy appetites, assigning it a new branch on the evolutionary tree

The journal Nature published an article in which researchers from the Russian Academy of Sciences and researchers from Canada, Great Britain and France presented a group of creatures that do not belong to any branch of the evolutionary tree of life. In fact, it adds a fairly large new branch to the evolutionary tree.

This is a supergroup that consists of single-celled creatures that prey on other single-celled creatures and feed on them. It is divided into two groups, one was named Nibbleridia – creatures that use tooth-like structures to swallow parts of their prey, and the other group was called Nebulidia – creatures that swallow the prey whole. Both groups represent a branch that is ancient in years but new to science called Provora.

The evolutionary tree of life

Many times we wonder how the animal world was created and how evolution works. The evolutionary tree of life, or the phylogenetic tree, is a graphic tool built in the form of a tree, which presents the estimated historical-evolutionary relationships between biological species – those that live today and those that have already become extinct, based on genetic or structural similarity between them. The branches of the tree describe how the many species on Earth evolved from common ancestors beginning with the beginning of life, billions of years ago.

The animal world is divided into three superkingdoms (Domains): Bacteria – creatures without a cell nucleus, Archaea – a group of ancient bacteria living in extreme conditions, and Eukaryotes – creatures with a cell nucleus, which include most of the living creatures known to us today, including plants, fungi, yeast, The animals and of course man. Each group that is defined as a superkingdom splits into branches called kingdoms such as the animal kingdom or the mushroom kingdom. From there the branches continue to split and become more and more defined, until at the end of the branch you reach the single species.

Every day new species are discovered in the world that are added to the tree of life, but in the new study it is not about another new species, but a completely new branch; A new supergroup that contains a large variety of carnivorous microorganisms, which are genetically different from any other life form that has so far been known on Earth. These creatures are placed in the evolutionary tree below the highest group, the super-kingdom, and above the kingdom, in the branch named ‘super group’.

Dividing the animal world from the general to the individual. Classification and taxonomic sorting VectorMine, Shutterstock

predatory microorganisms

The researchers discovered the new life form in a wide variety of saltwater and freshwater samples collected from around the world, for example from the coral reefs of Curaçao in the southern Caribbean Sea, the Black Sea, the Red Sea, the Pacific Ocean and the Arctic region. They noticed in the water samples strange, fast-swimming microorganisms with two tails. They noticed another strange phenomenon: these microorganisms devoured other single-celled creatures that were in their environment, such as protozoa, and these disappeared in a short time.

“I noticed that in some water samples there were tiny creatures with two tails, which moved around in place or swam very quickly. That’s how my hunt for them began,” said Denis Tikhonenkov, the first author of the article. “In the samples where these single-celled creatures were, all the other creatures disappeared within a day or two. How? They were just eaten. To grow the hungry creatures, you had to feed them other single-celled creatures.” That’s why the scientists called the microorganisms they discovered “the lions of the microbial world”.

Although this supergroup is widespread throughout the world and very diverse, the creatures that belong to it are numerically very rare. But despite their low numbers, they have great ecological importance, just as lions are rare in nature relative to the animals they prey on.

A graphical representation of the evolutionary relationships between biological species. The evolutionary tree of life VectorMine, Shutterstock

Classify the flora and fauna

Throughout history, humans have tried to sort and classify the animal and plant world into groups and subgroups. The field that deals with this is called taxonomy. In the past, taxonomists characterized creatures based on appearance, but when technologies were developed to isolate the genetic material and reproduce it in the laboratory, a change occurred, and scientists began to classify creatures according to their genetic sequence. The field of metagenomics, which is based on sequencing a large amount of genes, and sometimes sequencing the entire genome, has greatly contributed to the identification and characterization of new species of microorganisms. But even the advanced methods have limitations, here we are talking about very rare creatures and sometimes they are simply hard to find.

To discover the rare creatures and isolate enough cells for genetic characterization, scientists had to find a way to grow them in the laboratory. Growing these single-celled predators was not simple, in order for them to survive in laboratory conditions, a suitable mini-ecosystem had to be established and the predators provided with their food – the prey.

Finally, after a long and complex collaboration between researchers from Canada and Russia, which was greatly delayed due to the Corona epidemic and the war in Ukraine, the scientists discovered ten new carnivore species. Sequencing their genetic material revealed that carnivores are genetically, structurally and behaviorally significantly different from any other living creature on Earth. For example, when you compare the sequence of letters in the 18S rRNA gene, which is used in research to distinguish the differences between living creatures, you find that there are only six differences between a human and a vole (guinea pig). In contrast, the single-celled carnivores differ in 170 to 180 sites compared to any other creature that lives on Earth. Because they are so different from every other eukaryotic organism, they have been placed in a separate place and given their own new branch or supergroup.

Thanks to advanced molecular methods, the evolutionary tree changes and is updated all the time. Life forms that we did not know existed are revealed to the mornings and new data reshapes it. These life forms are not really new, they have been here for a long time and all we have to do is discover them.


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