Meeting Abstract

23.4  Jan. 5  Sucker-Arm Coordination in Octopus During Grasping and Manipulation of Objects GRASSO, Frank W.; Brooklyn College, the City University of New York fgrasso@brooklyn.cuny.edu

In natural settings octopuses use their arms and suckers in a variety of dexterous manipulation tasks, such as extracting prey from crevices and burrows, opening bivalve shells and arranging middens as barriers in front of their den entrances. Octopuses attach multiple suckers to surfaces for a power grasp which enables the octopus to move objects relative to its body. To transport or reposition objects octopuses have been observed to project an arm from their body, attach a group of distal suckers and pull an object to toward them by shortening the arm. They have also been reported bend the arm once suckers adhere producing dynamic joints where needed to move the object. The former behavior is loosely analogous to squid tentacle extension and prey capture. The later parallels vertebrate jointed manipulation albeit via dynamic joint induction. We investigated octopuses� use of suckers in object relocation tasks under controlled, reproducible laboratory conditions. Because larger suckers can generate larger adhesion forces we hypothesized that octopuses would prefer to use larger suckers toward the base of the arm when they were available for tasks requiring the arm to employ relatively greater force. We found, that a squid-like approach (deploying distal, and therefore small, suckers and then shortening the arm)was not commonly used in the tasks studied. Instead, in many cases the animals used combinations of arm-bends and different functional groups of suckers dynamically assigned to different roles. When animals were restricted to the use of a single arm they preferred significantly, to use suckers in the middle of the arm to support this coordinated arm-sucker activity. These results are consistent with a pattern of sophisticated sucker-arm coordination and are contrary to a view of suckers as passive agents reflexively supplying adhesion in reaction to surface contact.