Among invertebrates Octopus are acclaimed to be most
intelligent animals and have largest nervous system. Octopus, a Mollusc falls
under category of modern cephalopod. Other important soft shelled smart animals
that belong to the class Cephalopods are Cuttle fish, Squid and Nautilus.
While it is known that vertebrates with their distinct
nervous system are far more intelligent scientists are keen about investigating
the system that renders these invertebrates with superior cognitive skills.
Caroline Albertin and her colleagues of University of Chicago in an effort to
understand the basis for intelligence in Cephalopods have mapped the genome of
Octopus. The report published in the Nature journal is collaborative effort of
the University of Chicago, University of California Berkeley, University of
Heidelberg, Okinawa Institute of Science and Technology. The scientists have
carried out gene expression studies of 12 different tissues as well. They have
identified two genetic families whose presence is more pronounced than the
simpler Molluscs. These are the C2H2 Zinc-finger transcription proteins and the
protocadherin proteins that regulate neuronal development.
Octopus has uniquely shelled eight tentacles that serve as
prehensile arms, suckers, cameras and has effective colouring system to camouflage.
It has unusually large genome almost as large as the human genome and has 33,000
protein coding genes compared to 25,000 of human beings.
Sophisticated Cephalopods have nearly half a billion neuronal
cells as against 200 million in rat. These contribute to the extraordinary
observational learning, complex problem solving, task-dependent conditional
discrimination. Octopus has twice the number of Protocadherins genes than mammals.
Protocadherin proteins are responsible for synaptic specificity, short-range
interactions needed for circuit formation. These contribute to neuronal
complexity of Octopus and accounts of its unusually large sized brain. Even the
anatomy of various important organs is also peculiar. The tentacles have
independent computing capacity and hence even if they are separated from main
body they can execute cognitive tasks.
C2H2 transcripts are found in the nervous tissue and embryonic
tissues and have crucial role in cell fate determination, transposon silencing
and early development. Elevated transposon expression accounts for elevated
memory and learning. Interestingly, nearly half of the octopus genome is made
of transposons which are mobile. They translocate to new locations causing enhancement
or decrease of gene expression. Octopus has 18,000 Zinc-finger transcription
genes second to 20,000 genes of Elephants. These transcription factor genes
adjust the expression of other genes and in Octopus these regulates the genes
in suckers and in receptors of skin. Suckers have large number of genes that
code for the neuronal transmitter acetyl choline. Octopus has proteins
reflectins coded by six genes on skin. These proteins help in altering the
brightness of the light in several ways and in effectively disguising itself. Unlike
higher vertebrates where large number of gene duplications contributes to large
genomes Octopus genes have evolved genuinely in response to natural selection.
Unlike vertebrates, neurons in Octopus are not concentrated
in brain and spinal cord. But these travel to localised organs of the body like
tentacles/arms. They appear as protuberances and take up specialised function
depending upon their location. While brain can completely take over the control
of entire body, Octopus has a decentralised nervous system that allows the arms
to function autonomously. Hence they are less dependent on the long range
signal transmissions even. Precisely, this mechanism allows octopus to act
quickly and instinctively. Neurobiologists and Roboticists marvel this very
unique kind of intelligence characteristic of Octopus.
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