Octopuses have captured the human imagination for centuries, inspiring sagas of sea monsters from Scandinavian kraken legends to TV’s “Voyage to the Bottom of the Sea” and, most recently, Netflix’s less-threatening “My Octopus Teacher.” With their eight suction-cup covered tentacles, their very appearance is unique, and their ability to use those appendages to touch and taste while foraging further sets them apart.
In fact, scientists have wondered for decades how
those arms, or more specifically the suction cups on them, do their work,
prompting a number of experiments into the biomechanics. But very few have
studied what is happening on a molecular level. In a new report, Harvard
researchers got a glimpse into how the nervous system in the octopus’ arms (which
operate largely independently from its centralized brain) manage this feat.
The work published in Cell.
The scientists identified a novel family of sensors in
the first layer of cells inside the suction cups that have adapted to react and
detect molecules that don’t dissolve well in water. The research suggests these
sensors, called chemotactile receptors, use these molecules to help the animal
figure out what it’s touching and whether that object is prey.
“We think because the molecules do not solubilize
well, they could, for instance, be found on the surface of octopuses’ prey and
[whatever the animals touch],” said Nicholas Bellono, an assistant professor of
molecular and cellular biology and the study’s senior author. “So, when the
octopus touches a rock versus a crab, now its arm knows, ‘OK, I’m touching a
crab [because] I know there’s not only touch but there’s also this sort of
taste.'”
In addition, scientists found diversity in what the
receptors responded to and the signals they then transmitted to the cell and
nervous systems.
“We think that this is important because it could
facilitate complexity in what the octopus senses and also how it can process a
range of signals using its semi-autonomous arm nervous system to produce
complex behaviors,” Bellono said.
The scientists believe this research can help uncover
similar receptor systems in other cephalopods, the invertebrate family that also
includes squids and cuttlefish. The hope is to determine how these systems work
on a molecular level and answer some relatively unexplored questions about how
these creatures’ capabilities evolved to suit their environment.
“Not much is known about marine chemotactile behavior
and with this receptor family as a model system, we can now study which signals
are important for the animal and how they can be encoded,” said Lena van
Giesen, a postdoctoral fellow in the Bellono Lab and lead author of the paper.
“These insights into protein evolution and signal coding go far beyond just
cephalopods.”
Along with Giesen, other co-authors from the lab
include Peter B. Kilian, an animal technician, and Corey A.H. Allard, a
postdoctoral fellow.
“The strategies they have evolved in order to solve
problems in their environment are unique to them and that inspires a great deal
of interest from both scientists and non-scientists alike,” Kilian said.
“People are drawn to octopuses and other cephalopods because they are wildly
different from most other animals.”
The team set out to uncover how the receptors are able
to sense chemicals and detect signals in what they touch, like a tentacle
around a snail, to help them make choices.
Octopus arms are distinct and complex. About
two-thirds of an octopus’s neurons are located in their arms. Because the arms
operate partially independently from the brain, if one is severed it can still
reach for, identify, and grasp items.
The team started by identifying which cells in the
suckers actually do the detecting. After isolating and cloning the touch and
chemical receptors, they inserted them in frog eggs and in human cell lines to
study their function in isolation. Nothing like these receptors exists in frog
or human cells, so the cells act essentially like closed vessels for the study
of these receptors.
The researchers then exposed those cells to molecules
such as extracts from octopus prey and others items to which these receptors
are known to react. Some test subjects were water-soluble, like salts, sugars,
amino acids; others do not dissolve well and are not typically considered of
interest by aquatic animals. Surprisingly, only the poorly soluble molecules
activated the receptors.
Researchers then went back to the octopuses in their
lab to see whether they too responded to those molecules by putting those same
extracts on the floors of their tanks. They found the only odorants the
octopuses receptors responded to were a non-dissolving class of naturally
occurring chemicals known as terpenoid molecules.
“[The octopus] was highly responsive to only the part
of the floor that had the molecule infused,” Bellono said. This led the
researchers to believe that the receptors they identified pick up on these
types of molecules and help the octopus distinguish what it’s touching. “With
the semi-autonomous nervous system, it can quickly make this decision: ‘Do I
contract and grab this crab or keep searching?'”
While the study provides a molecular explanation for
this aquatic touch-taste sensation in octopuses through their chemotactile
receptors, the researchers suggest further study is needed, given that a great
number of unknown natural compounds could also stimulate these receptors to
mediate complex behaviors.
“We’re now trying to look at other natural molecules
that these animals might detect,” Bellono said.
No comments:
Post a Comment