Albertin, C.B.; Simakov, O.; Mitros, T.; Yan Wang, Z.; Pungor, J.R.; Edsinger-Gonzales, E.; Brenner, S.; Ragsdale, C.W., and Rokhsar, D.S. The octopus genome and the evolution of cephalopod neural and morphological novelties. Nature. 13 August 2015. Doi: 10.1038/nature14668 (Open access!)
Octopuses are curious creatures with lots of cool features, including most famously eight legs lined with suction cups that can be used to grab things, camera-like eyes, and an extraordinary ability to change color to blend in with their surroundings. Furthermore, octopuses exhibit behaviors that might be called intelligent, especially among their cephalopod (think squid, cuttlefish, nautilus) brethren, such as living in long-term mate pairs, building homes, and learning. Such complex behaviors are enabled by an intricate nervous system unique among invertebrates, and rivaling that of vertebrates. Intriguingly, octopus intelligence seems to have evolved via a different route than our vertebrate intelligence. While our nervous systems operate centrally, octopuses possess highly decentralized nervous systems. That is, their legs do not communicate directly with their brains, but essentially have minds of their own, which allow them to respond effectively to their environments. In fact, compared to a mouse an octopus possesses something like six times the number of axons (the branches of the nervous system responsible for transmission of short-distance signals).
To better understand the origins of octopus intelligence a multinational team lead by Caroline Albertin and Oleg Simakov sequenced the genome of the California two-spot Ocotopus (that’s Octopus bimaculoides to you Latin junkies), which they report in a recent issue of Nature.
Albertin and others utilized the same “shotgun” approach first used to sequence the human genome in 2003 to sequence the octopus genome. Shotgun sequencing is the modern method of choice for sequencing and involves repeated sequencing of short random fragments of DNA, which are then assembled by a computer. The genome only says so much without functional information about what it encodes, hence they also sequenced several transcriptomes that tell what genes are turned on where and when, improving the researchers chances of correctly assigning gene functions. The resulting octopus genome is 2.7 billion base pairs in length encoding about 34,000 proteins rivaling the 3 billion base pair 25,000 protein-encoding human genome.
Genome in hand, the team looked for patterns that might provide a basis for octopus intelligence in comparison to other invertebrates. They identified two gene families the protocadhedrins involved in the formation of nervous system development, and the lesser understood C2H2 zinc-finger family genes involved in gene regulation (turning genes on and off), that were greatly expanded (more abundant) in the octopus genome in relation to other invertebrates, and in common with vertebrates.
Inspecting the transcriptome data, the team observed increased expression of protocadhedrin and C2H2 zinc-finger genes in the neural tissues of embryonic and adult octopuses, supporting their role in nervous system construction and operation. Put simply, they discovered the capacity for the octopus to build a complex nervous system, as well as the potential for that nervous system to be manipulated through a sophisticated operating board of genetic switches.
The findings of Albertin, Simakov, and co-workers shed light into the origin of cephalopod intelligence in the modern octopus, providing a basis for differences in the decentralized nervous system of the octopus as compared to the centralized nervous system of the squid, which are thought to have diverged some 270 million years ago. Moreover, these findings hint at the phenomenon of “convergent evolution” whereby to distinct lineages, the vertebrates and invertebrates arrived at the same end, a complex nervous system, from distinct starting points. Perhaps most excitingly of all, the work of Albertin and others provides researchers interested in the ins and outs of the octopus a basis to answer a multitude of fascinating question about a truly strange creature of the deep.
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Abrahim is a PhD student at Scripps Institution of Oceanography in San Diego where he studies marine chemical biology.