Visual perception and camouflage response to 3D backgrounds and cast shadows in the European cuttlefish, Sepia officinalis

Abstract

To conceal themselves on the seafloor European cuttlefish Sepia officinalis express a large repertoire of body patterns. Scenes with 3-D relief are especially challenging because neither is it possible to directly recover visual depth from the 2-D retinal image, nor for the cuttlefish to alter its body shape to resemble nearby objects. Here we characterise cuttlefish's camouflage responses to 3-D relief, and to cast shadows, which are complementary depth cues. Animals were recorded in the presence of cylindrical objects of fixed (15mm) diameter, but varying in height, greyscale and strength of cast shadows, and to corresponding 2-D pictorial images. With the cylinders the cuttlefish expressed a ‘3-D’ body pattern, which is distinct from previously described Uniform, Mottle, and Disruptive camouflage patterns. This pattern was insensitive to variation in object height, contrast, and cast shadow, except when shadows were most pronounced, in which case the body patterns resembled those used on the 2-D backgrounds. This suggests that stationary cast shadows are not used as visual depth cues by cuttlefish, and that rather than directly matching the 2-D retinal image, the camouflage response is a two-stage process whereby the animal first classifies the physical environment and then selects an appropriate pattern. Each type of pattern is triggered by specific cues that may compete allowing the animal to select the most suitable camouflage, so the camouflage response is categorical rather than continuously variable. These findings give unique insight into how an invertebrate senses its visual environment to generate the body pattern response.

The brain structure and the neural network features of the diurnal cuttlefish Sepia plangon

“… 77 The complexity of camouflage tricks cuttlefish and squid demonstrate is also substantial, but again the former outstripping the latter. Cuttlefish camouflage contains a combination of cryptic coloration, skin texture and arm posture to conceal itself into the 3D characters of the surrounding scene 1 , 3 , 12 , 96 ( Video S4 ). By contrast, the squid mainly relies on color changes on body surface to mimic the 2D background by manipulating colors to match with substrate while reaching close to floor and switching to countershading while hovering in water column.…”

Role of body size and shape in animal camouflage

“…This strategy can make the prey appear larger or smaller than the actual size or blend with the background (Kelley et al., 2022 ). For example, the European cuttlefish Sepia officinalis alters its body color pattern to create depth cues or illusionary depths resembling 3D objects in the background through 3D background matrix and shadows (El Nagar et al., 2021 ). The effectiveness of 3D camouflage depends on the prey's characteristics, such as body shape, and on the predator's visual system, particularly whether they have binocular vision.…”

“…This strategy can make the prey appear larger or smaller than the actual size or blend with the background (Kelley et al, 2022). For example, the European cuttlefish Sepia officinalis alters its body color pattern to create depth cues or illusionary depths resembling 3D objects in the background through 3D background matrix and shadows (El Nagar et al, 2021).…”

Role of Body Size and Shape in Animal Camouflage

“…This strategy can make the prey appear larger or smaller than the actual size or blend with the background (Kelley et al, 2022). For example, the European cuttlefish Sepia officinalis alters its body color pattern to create depth cues or illusionary depths resembling 3D objects in the background through 3D background matrix and shadows (El Nagar et al, 2021). The effectiveness of 3D camouflage depends on the prey's characteristics, such as body shape, and on the predator's visual system, particularly binocular vision.…”