Cephalopods such as octopuses, squids and cuttlefish are highly intelligent animals with complex nervous systems. Octopus brains, in particular, have developed remarkably over time due to an expansion of their pool of micro-ribonucleic acids (RNAs).
If we go back far enough in evolutionary history, we will encounter the last common ancestor of humans and cephalopods: a primitive, worm-like animal with minimal intelligence and simple eyes. Later, the animal kingdom was divided into two groups of organisms: those with a backbone and those without, it shows Phys.org.
While vertebrates, especially primates and other mammals have gone through complex brain development with various cognitive abilities, invertebrates have not undergone the same evolutionary process. The only exception? Cephalopods.
Fundamental role of microRNAs in complex brain development
Scientists have long wondered why a nervous system like this was only able to develop in molluscs.
An international team from the Max Delbrück Research Center in Berlin, Germany and Dartmouth College in the US has advanced a possible reason why the brain of cephalopods has developed in such a remarkable way.
In an article published in Science Advancesthe researchers explained that an octopus possesses an extensive pool of microRNAs in its neural tissue, thus reflecting similar developments that have occurred in vertebrates.
“So this is what connects us to octopuses,” said Professor Nikolaus Rajewsky, scientific director of the Max Delbrück Center Institute for Medical Systems Biology in Berlin and author of the paper.
Rajewsky also explained that this finding likely means that microRNAs play a fundamental role in the development of a complex brain.
Largest expansion of microRNA families in the animal world found in octopuses
The marine research station Stazione Zoologica “Anton Dohrn” in Naples, Italy, sent Rajewsky samples of 18 different types of tissues from dead octopuses. The results of the analyzes were surprising.
“Indeed, there was a large amount of RNA editing going on, but not in the areas that we thought were of interest,” Rajewsky said. The most interesting finding was actually the dramatic expansion of a well-known group of RNA genes, the microRNAs, he said.
In total, 42 new families of microRNAs were found – especially in neuronal tissue and especially in the brain. Given that these genes have been conserved during the evolution of cephalopods, the team concludes that they were clearly beneficial to animals and are therefore functionally important.
“This is the third largest expansion of microRNA families in the animal world and the largest outside of vertebrates. To give you an idea of the scale, oysters, which are also molluscs, have acquired only five new families of microRNAs from the last ancestor they shared with octopuses – while octopuses have acquired 90,” says lead author Grygoriy Zolotarov, a Ukrainian scientist who interned in Rajewsky’s lab.
Oysters, Zolotarov adds, aren’t exactly known for their intelligence.
The signs of intelligence that octopuses emit
From an evolutionary perspective, octopuses are unique among invertebrates. Octopuses have both a central brain and a peripheral nervous system, meaning one that is capable of acting independently. If an octopus loses a tentacle, it remains sensitive to touch and can still move. The reason octopuses are the only ones to have developed such complex brain functions may be that they use their arms intentionally – as tools to open shells, for example.
Octopuses also show other signs of intelligence. They are very curious and can remember things. What’s more, octopuses can recognize people and even like some more than others. Researchers today believe that they can even dream because their skin changes color and structure during sleep.
The research team plans to apply a technique developed in Rajewsky’s lab that will make cells in octopus tissue visible at the molecular level.