New research shows how octopuses may have evolved

A new paper in Genome Biology and Evolution suggests that a type of octopus may have lost its genetic code in the process of developing a shell.

The Argonauta argo is an animal that lives in the tropics. Eggs are protected by a spiral, shell-like case in the mouth of a female argonaut. The origin of the egg case has been a topic of research for many years. It appears to be the same shell as the pearly nautilus, which has a hard shell and lives on the ocean floor, but that may be a coincidence.

The argonaut's egg case and the nautilus's shell are not the same as they look on the small scale. The egg case may have evolved from the shell.

A team of researchers from Japan, led by Masa-aki Yoshida and Davin Setiamarga, tried to show how the species adapted to the open ocean and obtained its shell-like egg case by using the draft genomes of the species. It was difficult for scientists to keep the animals in aquaria for research. The location in the Sea of Japan was perfect for fresh samples.

Several features related to shell evolution and egg case formation can be found in the new genome data. The researchers discovered that most of the egg case genes were not used to make shells in other species. The shells of the distant ancestors of the argonaut octopuses probably did not evolve into egg cases.

The argonaut genome shows that the break in synteny is not a general trait of this group. Contrary to popular belief, the evolution of the cephalopods is not a distinct one. The research of metazoan, mollusk, and cephalopod genomes has remained largely unexplored thus far.

More information: Masa-aki Yoshida et al, Gene recruitments and dismissals in the argonaut genome provide insights into pelagic lifestyle adaptation and shell-like eggcase reacquisition, Genome Biology and Evolution (2022). DOI: 10.1093/gbe/evac140