Size Matters: Observed and Modeled Camouflage Response of European Cuttlefish (Sepia officinalis) to Different Substrate Patch Sizes during Movement

Abstract

Camouflage is common throughout the phylogenetic tree and is largely used to minimize detection by predator or prey. Cephalopods, and in particular Sepia officinalis cuttlefish, are common models for camouflage studies. Predator avoidance behavior is particularly important in this group of soft-bodied animals that lack significant physical defenses. While previous studies have suggested that immobile cephalopods selectively camouflage to objects in their immediate surroundings, the camouflage characteristics of cuttlefish during movement are largely unknown. In a heterogenic environment, the visual background and substrate feature changes quickly as the animal swim across it, wherein substrate patch is a distinctive and high contrast patch of substrate in the animal's trajectory. In the current study, we examine the effect of substrate patch size on cuttlefish camouflage, and specifically the minimal size of an object for eliciting intensity matching response while moving. Our results indicated that substrate patch size has a positive effect on animal's reflectance change, and that the threshold patch size resulting in camouflage response falls between 10 and 19 cm (width). These observations suggest that the animal's length (7.2-12.3 cm mantle length in our case) serves as a possible threshold filter below which objects are considered irrelevant for camouflage, reducing the frequency of reflectance changes-which may lead to detection. Accordingly, we have constructed a computational model capturing the main features of the observed camouflaging behavior, provided for cephalopod camouflage during movement.

Camouflage in a dynamic world

“…Minimisation of motion signals may be why cuttlefish, which are capable of rapid colour change [31], switch to low contrast patterns when moving [32]. They also change their mean whole-body reflectance as they move over light or dark substrates [33], but only if the patch size is larger than their body length [34]; again consistent with reducing a motion signal (Figure 2).…”

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

“…When we classify objectsfor example, as chairs or sofaswe make categorical decisions (Harnad, 1987), and there is evidence that cuttlefish camouflage operates in a similar way. Studies have shown that there are thresholds of visual stimuli that trigger certain responses; the sizes and aspect ratios of black and white contrasts needed to elicit a white square response (Chiao and Hanlon, 2001b), and the patch size on a uniform background needed to elicit a response in a moving cuttlefish (Josef et al, 2017). Cuttlefish are able to switch from background matching and being cryptic to masquerading as an inedible object.…”

“…In such conditions, camouflaging as an average visual aspect of the scene would break the camouflage, as it would look neither like the background nor like another present object; hence, there could be thresholds between visual cues that trigger camouflage responses to switch directly from one to the other. As prey, it would be most adaptive to develop camouflage thresholds that are similarly sensitive to the visual cues that will be noticed by the eyes of the predators (Josef et al, 2017). An analogous phenomenon was noted when the cuttlefish was on a uniform background scene containing only one object about the size of its mantle, where a choice needed to be made between matching the background or resembling the object.…”

Cephalopod Experimental Projected Habitat (CEPH): Virtual Reality for Underwater Organisms

“…Cephalopods multilayered and sophisticated skin structure consists of a dense network of pigmented muscle-driven chromatophore cells, which are neurally stimulated to actuate and affect local skin coloring (reviewed in Hanlon and Messenger, 1998). When camouflaging, these visually-oriented mollusks alter their appearance to match their surroundings which, providing researchers a glimpse into the animal's apparent visual perspective (Messenger, 1977;Muntz and Gwyther, 1988;Hanlon and Messenger, 1998;Chiao and Hanlon, 2001b;Barbosa et al, 2007;Hanlon et al, 2009;Josef et al, 2012Josef et al, , 2017Schwarz, 2015). Theoretically, by manipulating the visual environment it might be possible to characterize and test the background effect and eliciting these various displays.…”

“…More recently, computational technologies have been utilized in hopes of objectively quantifying and categorizing cephalopods skin patterns (Barbosa et al, 2008;Hanlon et al, 2009;Chiao et al, 2010;Zylinski et al, 2010;Josef et al, 2012Josef et al, , 2017Orenstein et al, 2016) and other marine organisms behavior under gradient sensory cues (Berdahl et al, 2013). Modulating the visual surroundings while concurrently studying an organism's behavior provides a subjective and interactive modality which opened new avenues for behavioral, physiological and psychological research.…”