The octopus is one of the most intelligent invertebrate animals. It has an extensive nervous system, much of which is distributed by its eight tentacles. Each of these has a central nerve that branches to the suckers, each of which has a nerve ganglion dedicated to its control. The tentacles allow the octopus to explore its environment in a way that is inaccessible to animals without them. This gives them an important advantage to obtain food in the niche they occupy.
It is known that suction cups, in addition to the sense of touch, also have the ability to “taste” what the octopus touches. The nerve ganglia of each of the octopus’ tentacle suckers function as a kind of small brain dedicated to the autonomous control of each sucker. The ganglia process information that is communicated to them from the surface of the sucker, according to what it may be touching at any given time.
It has long been known that the edges of suckers possess receptor cells similar to those of other animals. These cells must have detector molecules that capture information both on the mechanical properties of surfaces and on their chemical composition. The latter is interesting, because the chemical composition of odorous substances is different in water than in air. The most accepted idea is that aquatic animals detect substances soluble in water that are dragged by currents.
However, this idea does not seem to be completely true, since some marine animals are capable of detecting substances that do not dissolve in water and, for this reason, are found attached to the surfaces of the oceans and seas. For example, mollusks produce a series of insoluble substances, oily in nature, called terpenoids, which would disperse on surfaces instead of being washed away by water. Terpenoids are one of the most abundant classes of organic molecules in nature and are produced by many animals as a means of defense, since many of them are toxic.
Researchers from Harvard University, in the USA, decided to study in detail the detector cells located on the edges of the suckers of a species of octopus with the curious name of the two-spotted California octopus (Octopus bimaculoides). This animal reacts differently depending on whether or not the surface it is presented to explore contains terpenoids attached to it.
The researchers find that, as expected, the sucker receptor cells have molecules on their surface capable of detecting terpenoids and related substances, suggesting that the animal may avoid capturing toxic prey. However, in their studies, they also find that these same molecules on the surface of cells are equally capable of capturing, at the same time, information about the mechanical properties of the surfaces to which the suction cups adhere. These receptor molecules capture both tactile information and olfactory or taste information.
This type of double receptor molecules had not been identified before in any other animal, so this discovery now allows us to raise other interesting questions, including whether cuttlefish and squids, animals with tentacles but capable of floating and swimming, also have these double receptor molecules or if, on the contrary, these suppose a particular adaptation of the octopus, due to its way of life.
Referencia: van Giesen et al., Molecular Basis of Chemotactile Sensation in Octopus, Cell (2020),
Jorge Laborda, November 8, 2020
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