Sensorial Hierarchy in Octopus vulgaris' s Food Choice: Chemical vs. Visual

Abstract

Octopus vulgaris possesses highly sophisticated sense organs, processed by the nervous system to generate appropriate behaviours such as finding food, avoiding predators, identifying conspecifics, and locating suitable habitat. Octopus uses multiple sensory modalities during the searching and selection of food, in particular, the chemosensory and visual cues. Here, we examined food choice in O. vulgaris in two ways: (1) We tested octopus's food preference among three different kinds of food, and established anchovy as the preferred choice (66.67%, Friedman test p < 0.05); (2) We exposed octopus to a set of five behavioural experiments in order to establish the sensorial hierarchy in food choice, and to evaluate the performance based on the visual and chemical cues, alone or together. Our data show that O. vulgaris integrates sensory information from chemical and visual cues during food choice. Nevertheless, food choice resulted in being more dependent on chemical cues than visual ones (88.9%, Friedman test p < 0.05), with a consistent decrease of the time spent identifying the preferred food. These results define the role played by the senses with a sensorial hierarchy in food choice, opening new perspectives on the O. vulgaris' predation strategies in the wild, which until today were considered to rely mainly on visual cues.

Keywords: Octopus vulgaris; cephalopod; cephalopod behaviour; chemical cues; food choice; octopus sense organs; problem-solving; visual cues.

Figure 1

Octopus’s problem-solving abilities [26,27,28,29,30,31,32] through learning and memory abilities [19,33,34,35,36,37,38,39,40,41,42] (associative learning [43,44,45], spatial memory [46,47,48], visual learning [43,49,50,51], chemo-tactile learning [52], long-term and short-term memory [34,38,39,53,54]).

Figure 2

Experimental design to establish the sensorial hierarchy in food choice in Octopus vulgaris between chemical and visual cues. Food preference test (FP); food types provided in the transparent screw-jars with pierced lids (T1), positive control, both chemical and visual cues; food types in transparent screw-jars with no-pierced lids (T2), only visual cues; food types in blind screw-jars with pierced lids (T3), only chemical cues; food types in screw-jars with pierced lids with outside a photo of food (anchovies, clam, mussel) that is different from the food inside (T4), chemical true and visual false cues; food types inside blind screw-jars with no-pierced lids as control (T5), negative control, both chemical and visual cues are absent.

Figure 3

Violin plot of the time spent (Δt) by Octopus vulgaris in problem-solving. T1 combined chemical and visual discriminations; T2 only visual discrimination; T3 only chemical discrimination; T4 real chemical and false visual discriminations; T5 negative control. Δt (s): time spent to choose the jar to open, from the very first touch to the grab and wrap of the jar starting to open it. Wilcoxon matched-pairs test vs T1: significance is denoted with asterisks * for p < 0.05.

Figure 4

Visual vs. chemical perception in Octopus vulgaris. Percentage of the successful decisions to open as first the jar that contained the preferred food, based on chemical (purple) or visual (orange) cues. Wilcoxon matched-pairs test vs. T1 significance is denoted with asterisks * for p < 0.05.