Abstract
Living under intense predation pressure, octopuses evolved an effective and impressive camouflaging ability that exploits features of their surroundings to enable them to “blend in.” To achieve such background matching, an animal may use general resemblance and reproduce characteristics of its entire surroundings, or it may imitate a specific object in its immediate environment. Using image analysis algorithms, we examined correlations between octopuses and their backgrounds. Field experiments show that when camouflaging, Octopus cyanea and O. vulgaris base their body patterns on selected features of nearby objects rather than attempting to match a large field of view. Such an approach enables the octopus to camouflage in partly occluded environments and to solve the problem of differences in appearance as a function of the viewing inclination of the observer.
Highlights
Predation is a strong evolutionary driving force selecting for the development of various defensive mechanisms and behaviors, including cryptic coloration and camouflage [1]
Cephalopods, octopuses, possess the remarkable ability to change their body patterns to match changes in their visual background, categorized and described in detail for Octopus cyanea by Hanlon and Messenger [12].Taking a different approach, crypsis has been described as a range of strategies that prevent detection [13]
The camouflaging animal needs to choose whether to attempt to match a large part of its background or a common, smaller, yet more specific structure in its immediate environment. In this field study we addressed the following question: does an octopus take into account its entire nearby visual field to achieve what is termed ‘‘general resemblance’’ [3], or does it sample specific features of structures in its surroundings toward what is known as ‘‘deceptive resemblance’’ ([3], reviewed in [31])? Both species examined (O.cyanea and O.vulgaris) are known as shallow water diurnal predators [40,41], each with a wide repertoire of body patterns [30]
Summary
Predation is a strong evolutionary driving force selecting for the development of various defensive mechanisms and behaviors, including cryptic coloration and camouflage [1]. Background matching is a dynamic, visually driven process, in which the animal assesses a range of background variables such as contrast, brightness, edge, orientation, and size of objects when deciding what camouflage pattern to display [12,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29] To create such a wide variety of body patterns (described in detail by Borreli [30] for various cephalopod species), an octopus uses its sophisticated skin, which contains pigmented chromatophore organs, reflecting iridophores, and light scattering leucophores (reviewed in [12]). O. cyanea is found throughout the Indo-Pacific region, mostly in coral reef environments, while O. vulgaris is common in temperate climate regions where it is frequently found on gravel and in rocky areas
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