Octopuses taste their food when they touch it with their arms

octopus

The California two-spot octopus

Minden Pictures/Alamy

Octopuses can taste their prey before eating it by using their arms to “lick” it, which researchers say adds to evidence that the cephalopods’ eight appendages are analogous to tongues with “hands” and “brains”.

Octopus arms are lined with suckers that include cells for neural processing of touch and taste signals. These allow them to determine if an animal is good to eat or is toxic, says Nicholas Bellono at Harvard University. That is particularly useful since octopuses tend to “blindly” hunt, sticking their limbs into holes and crevices to find hidden prey.

Bellono and his colleagues studied the sucker cells of California two-spot octopuses (Octopus bimaculoides) microscopically and at a molecular level, finding that some respond to touch and others to the “taste” of chemicals in the water, with branched endings typical of sensory cells.

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They then used electrophysiology, which measures cells’ electrical activity, to test how sensitive the suckers’ taste and touch receptors were to different kinds of flavours and odours, respectively. The scientists determined that the receptors reacted to water-soluble chemicals, like bitter chloroquine, as well as to chemicals that don’t dissolve well in water, such as those emitted by toxic prey, says Bellono.

Many marine animals, including octopuses, have olfactory organs that probably detect water-soluble chemicals and possibly some poorly soluble ones. However, this “underwater smelling” is usually thought to occur over distance in the water, like the way noses function over distance in the air. Poorly soluble molecules require close range for detection, which is made easier by direct contact, similar to how tongues work.

Octopuses do actually possess a tongue-like organ in their mouths called the radula, which cuts and scrapes prey, especially shellfish. Yet it doesn’t seem capable of taste. The radula acts “more like teeth”, says Bellono.

So far, the taste/touch receptors “seem to be specific to the suckers”, says Bellono.

Journal reference: Cell, DOI: 10.1016/j.cell.2020.09.008

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source: newscientist.com