Monday, September 14, 2015

The octopus: alternative evolution toward learning and intellect?

Common octopus by Albert Kok

The evolutionary drive toward complexity and specifically organizational, neuronal complexity is highly evident during evolution. Octopuses, which have independently evolved camera-type eyes (with a lens, iris and retina), a highly derived early embriogenesis, closed circulatory systems and large brains, are a very good case study for parallel evolution. The recently sequenced octopus genome shows a spectacular example of the evolutionary drive toward greater complexity. The octopus probably achieved the limit of intellectual, organizational complexity that is possible in a non vertebrate animal. They are among the very few animals that are known to master tool use. Octopuses display extraordinarily sophisticated behaviors, including complex problem solving, task-dependent conditional discrimination, observational learning and spectacular displays of camouflage. Its dexterous arms are lined with hundreds of suckers that function as specialized tactile and chemosensory organs, and they have an elaborate special pigments containing cell system that enables rapid changes in appearance by direct neural control. Vastly modified in size and organization relative to other mollusks, the octopus nervous system is diffuse, with only one third of it is located inside the actual brain. Axial nerve cords in each arm function with some functional autonomy. Altogether in these structures nearly half a billion neurons, more than six times the number of mouse brain, are contained.

In early 2012 dozens of researchers agreed to work together to uncover the octopus sequence, the largest-known genome in the invertebrate world. Since the octopus has more genes (33, 000) than that of humans (20,000 to 25,000), the work has been especially difficult. The collaboration of scientists has payed off, as the octopus genome was recently published in the journal Nature. The octopuses radically different evolutionary path to intelligence from that of vertebrates is an amazing puzzle and has huge evolutionary importance. In octopuses a sophisticated neuronal wiring system forms throughout their entire bodies, which allows fast and intricate camouflage by expanding and contracting pigment filled sacks within milliseconds. This regulation can change overall color and even patterning in a blink of an eye. This complex neuronal network also empowers the octopus complex sensing with its suckers. Genes, known to be involved in developing complex neural networks in mammals is shared with the octopus. RNA editing is a molecular process through which some cells can make discrete changes to specific nucleotide sequences within a RNA. Shared with humans and other animals, octopuses mastery of this molecular process might help them regulate highly organized, concerted nerve firings. The new genetic analysis also shows the genes ability to move around on the genome, which might play a role in boosting learning and memory. Gene duplication, a well known evolutionary step in vertebrates, seems to be missing in octopuses, which makes their intellectual and organizational complexity all the more remarkable.

The octopus genome demonstrates the power of evolution to enhance complexity in the living world. Although they display impressive learning ability and some purposeful behavior, octopuses do not form emotions, which is the basis of intellectual abilities of mammals and birds. However, this does not mean that they are not engaged in some of the funniest purposeful behavior: Judge for yourself!

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