Many cephalopods like octopus, cuttlefish and squid are remarkably intelligent, especially considering the fact that they are all invertebrates. Now, a team of scientists have worked to uncover how the animals evolved to have such complex nervous systems due to a genetic ability.
Evolutions of vertebrates and invertebrates
According to the Max Delbruck Center for Molecular Medicine, humans and cephalopods have a common ancestor which was a primitive wormlike animal that had simple eyespots and minimal intelligence. Since that time, the animal kingdom bifurcated into two different groups—those with backbones and those without.
Many of the vertebrates, animals with backbones, went on to evolve large and complex brains that brought with them different levels of cognitive abilities. Invertebrates, on the other hand, continued to mostly evolve with relatively simple nervous systems and rudimentary “intelligence,” with one major exception—cephalopods.
Octopus: Unique among vertebrates
Octopuses are unique among invertebrates from an evolutionary perspective. They have a central brain along with a peripheral nervous system that is capable of acting independently. They have been observed using these arms almost like tools, using them to open shells, for instance.
They are also naturally curious animals that are also capable of remembering things. Some researchers believe that they can even dream, since they sometimes change their colour and skin structure while sleeping.
Micro RNAs and neural tissue
The reason why Octopuses were able to develop such complex brains and cognitive abilities has remained a scientific enigma for a long time. But now, a team of scientists from the Max Delbruck Center and Dartmouth College have put forward a possible reason as to why this could have happened, published in the journal Science Advances.
In the paper, scientists explain that octopuses have a “highly expanded repertoire” of microRNAs in their neural tissue. MicroRNAs are small RNA molecules that are involved in the formation of RNA molecules. The scientists assert that these microRNAs played an important role in the development of complex octopus brains, reflecting similar developments that happened with vertebrates.
Earlier research has discovered that a lot of RNA editing occurs with these cephalopods, which means that they make substantial use of some enzymes that can recode their RNA. To investigate this further, the scientists collaborated with the Stazione Zoologica Anton Dohrn marine research station in Naples to obtain 18 different tissue types from dead octopuses.
The results from the analyses of the samples turned out to be surprising. “There was indeed a lot of RNA editing going on, but not in areas that we believe to be of interest,” said Nikolaus Rajewsky, the last author of the paper, in a press statement. Rajewsky is the Scientific Director of the Berlin Institute for Medical Systems Biology of the Max Delbrück Center (MDC-BIMSB) and head of the Systems Biology of Gene Regulatory Elements Lab.
The researchers’ most significant discovery was a significant expansion of microRNAs, with them discovering a total of 42 new microRNA families in the neural tissue and mostly in the brain.
Based on the fact that these genes were conserved during cephalopod evolution, the team concluded that they were functionally important and preserved because they were beneficial to the animals.
“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 just five new microRNA families since the last ancestors they shared with octopuses – while the octopuses have acquired 90,” says lead author Grygoriy Zolotarov, in a press statement.
According to Zolatarov, the researchers’ molecular-biological tools are limited because octopuses are not typical model organisms. Due to this, they don’t yet know which types of cells express the microRNAs.