Chemotactic behaviour inOctopus

Summary

• 1. Small octopuses,Octopus vulgaris, (150 g) were blinded by section of the optic nerves to eliminate the use of visual cues. The animals were placed in a transparent Plexiglas tube (9 cm × 60 cm) that was continuously perfused with fresh sea water, and their behaviour was observed following the introduction of single organic compounds at known concentrations (Fig. 1).

• 2. Alterations in the ventilation rhythm (puffing) were elicited by glutamic acid 10⁻⁴ mol/l, glycine 10⁻⁴ mol/l and adenosine 5′-monophosphate (AMP) 10⁻⁷ mol/l. Arm waving and the forced expulsion of water through the siphon (blowing) were also observed with the same stimuli. Sea water controls showed significantly lower rates of response (Fig. 2).

• 3. Locomotion was elicited by glutamic acid 10⁻⁴ mol/l, glycine 10⁻³ mol/l, and AMP 10⁻⁶ mol/l (Fig. 2). The direction of locomotion was invariably upstream (51 trials). Because the stimuli were introduced to either the right or the left of a partition which bisected the upper third of the experimental tube, it was possible to evaluate the animal's perception of stimulus location. Two criteria were used: the entry of an animal into the space at either side of the partition, and the initial distribution of an animal's probing arms on the two sides (Table 2). In both cases, the results indicate an orientation towards the stimulus source, i.e. chemotaxis.

• 4. The frequency of responding, for all types of response, decreased from the first to the last trial in each testing session (Fig. 3). Sensitization was demonstrated by giving theOctopus a small piece of fish between stimulus trials (Fig. 4).

• 5. The suckers on the arms of theOctopus are believed to be the sensory structures responsible for the observed behaviours. The chemical sense may be an important adjunct to vision in the search for food under natural conditions.