Deliciously fetching behaviour

um...

Architeuthis
Supporter
#1
This week’s Nature contains a brief article describing some observations of octopus fetching movements made by the “Octopus Group” at Hebrew University. After an octopus has grasped a tasty morsel in one of its arms, it often transfers the item to its mouth using a movement reminiscent of articulated appendages. Here’s what happens (sorry if this is a bit clunky):

First, the food item is grasped at some point on the arm. Next, the octopus stiffens the arm into a “quasi-articulated” structure resembling three segments and three “joints”—sort of like your arm. The prey is grasped in the part that corresponds to your hand, which we’ll call the distal segment. The next segment towards the body, what would be your forearm, we’ll call the medial segment. Between these two segments, the octopus forms a bend (the distal bend) which functions as the “wrist”. The last segment, closest to the octopus’s body, is called the proximal segment and corresponds to your upper arm. The octopus forms another bend (the medial bend) between the medial and proximal segments, and this acts pretty much like your elbow. The last joint, the “shoulder” or proximal bend, occurs at the base of the arm. The fetching motion consists mainly of a rotation around the medial bend which brings the distal segment close to the base of the arm, followed by a rotation around the distal bend that brings the food item to the mouth for munching. The researchers observed that:
  • The lengths of the proximal and medial segments remained essentially constant during the fetching movement;
  • The lengths of the proximal and medial segments were close to being equal;
  • The length of the distal segment tended to shorten as the movement progressed;
  • The lengths of the medial and proximal segments varied according to the location on the arm at which the item was initially grasped.

Isn’t that neat? The octopus could bring the food to its mouth in an enormous number of ways, given the freedom of motion of its arms, but it actually does so in a “simple” way that resembles the motion used by an animal burdened with a skeleton (internal or external). Here’s what the authors had to say about that:

Fetching seems to be an example of evolutionary selection of solutions that are similar even though they are based on quite different mechanisms — on morphology in arthropod and vertebrate limbs, and on stereotypical motor control in the octopus. This functional convergence suggests that a kinematically constrained, articulated limb with two segments of almost equal length is the optimal design for accurately moving an object from one point to another.
Anyway, here’s a figure that might help you to understand what the heck I was trying to say:


L1 = length of proximal segment
L2 = length of medial segment
L3 = length of distal segment


All of this courtesy of: Sumbre G, Fiorito G, Flash T, Hochner B (2005). Motor control of flexible octopus arms. Nature 433:595-596.


And here’s a movie of a wunderpus’s fetching behaviour:

Small (~1.3 MB)
Large (24 MB)
 

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Tintenfisch

Architeuthis
Staff member
Moderator
#4
Wow, neato. I'll have to watch Slime at the aquarium and see if she does the same thing when retrieving clusters of eggs that have detached from the brood in her cave - we saw her scooping some renegade bunches back into her lair the other day, but weren't really watching for particular arm geometry.
Thanks for that!
 

Melissa

Larger Pacific Striped Octopus
Supporter
#6
The author of the Nat. Geo. piece is enthusiastic enough for TONMO, calling octos "those boneless, brainy, denizens of the deep".

What do you make of the picture of the "common octopus"?

Melissa
 

erich orser

Architeuthis
Supporter
Registered
#7
"Common"...

I find such class-based labels archaic in nature and rather offensive. Proletariat octopus of the world unite against your aristocratic/Capitalist exploiter octopus oppressors! We'll be having a meeting at the bookstore right off campus this evening; you know, the one with the nice juice bar right next to the Hemporium boutique...

Actually, I think it's just good old o.vulgaris.
 

um...

Architeuthis
Supporter
#8
:lol: Good old O. vulgaris, the completely classless octopus. :heee:

Hillary Mayell said:
When hunting and grabbing dinner, the octopus uses all the flexibility the arm is capable of.
Really? I doubt that is strictly true, since researchers from the same group at the Hebrew University have also documented stereotypical reaching behaviour in octopuses. Someone here mentioned that study a while back, and it's probably worth revisiting. The fetching behaviour described here is also probably not absolute, but it would make sense to me that an octopus should tend to limit itself to a subset of its virtually limitless possible movements. Most of those possibilities would end up being inefficient and wasteful of neural resources, wouldn't they? Similarly, a person could move around with a different silly walk each day, but only a very odd person would ever do that on purpose.

I wonder what that 100 foot octopus is grabbing for dinner? :goofysca:
 

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