Contact chemoreception in multi-modal sensing of prey by Octopus.

Octopuses have keen vision and are generally considered visual predators, yet octopuses predominantly forage blindly in nature, inserting their arms into crevices to search and detect hidden prey. The extent to which octopuses discriminate prey using chemo- versus mechano-tactile sensing is unknown. We developed a whole-animal behavioral assay that takes advantage of octopuses' natural searching behavior to test their ability to discriminate prey from non-prey tastes solely via contact chemoreception. This methodology eliminated vision, mechano-tactile sensing and distance chemoreception while testing the contact chemosensory discriminatory abilities of the octopus arm suckers. Extracts from two types of prey (crab, shrimp) and three types of non-prey (sea star, algae, seawater) were embedded in agarose (to control for mechano-tactile discrimination) and presented to octopuses inside an artificial rock dome; octopuses reached their arms inside to explore its contents - imitating natural prey-searching behavior. Results revealed that octopuses are capable of discriminating between potential prey items using only contact chemoreception, as measured by an increased amount of sucker contact time and arm curls when presented with prey extracts versus non-prey extracts. These results highlight the importance of contact chemoreception in the multi-modal sensing involved in a complex foraging behavior.

Dark scene elements strongly influence cuttlefish camouflage responses in visually cluttered environments.

This study investigated how cuttlefish (Sepia officinalis) camouflage patterns are influenced by the proportions of different gray-scales present in visually cluttered environments. All experimental substrates comprised spatially random arrays of texture elements (texels) of five gray-scales: Black, Dark gray, Gray, Light gray, and White. The substrates in Experiment 1 were densely packed arrays of square texels that varied over 4 sizes in different conditions. Experiment 2 used substrates in which texels were disks separated on a homogeneous background that was Black, Gray or White in different conditions. In a given condition, the histogram of texel gray-scales was varied across different substrates. For each of 16 cuttlefish pattern response statistics c, the resulting data were used to determine the strength with which variations in the proportions of different gray-scales influenced c. The main finding is that darker-than-average texels (i.e., texels of negative contrast polarity) predominate in controlling cuttlefish pattern responses in the context of cluttered substrates. In Experiment 1, for example, substrates of all four texel-sizes, activation of the cuttlefish "white square" and "white head bar" (two highly salient skin components) is strongly influenced by variations in the proportions of Black and Dark gray (but not Gray, Light gray, or White) texels. It is hypothesized that in the context of high-variance visual input characteristic of cluttered substrates in the cuttlefish natural habitat, elements of negative contrast polarity reliably signal the presence of edges produced by overlapping objects, in the presence of which disruptive pattern responses are likely to achieve effective camouflage.

Stretchable surfaces with programmable 3D texture morphing for synthetic camouflaging skins.

Technologies that use stretchable materials are increasingly important, yet we are unable to control how they stretch with much more sophistication than inflating balloons. Nature, however, demonstrates remarkable control of stretchable surfaces; for example, cephalopods can project hierarchical structures from their skin in milliseconds for a wide range of textural camouflage. Inspired by cephalopod muscular morphology, we developed synthetic tissue groupings that allowed programmable transformation of two-dimensional (2D) stretchable surfaces into target 3D shapes. The synthetic tissue groupings consisted of elastomeric membranes embedded with inextensible textile mesh that inflated to within 10% of their target shapes by using a simple fabrication method and modeling approach. These stretchable surfaces transform from flat sheets to 3D textures that imitate natural stone and plant shapes and camouflage into their background environments.

Dynamic camouflage by Nassau groupers Epinephelus striatus on a Caribbean coral reef.

This field study describes the camouflage pattern repertoire, associated behaviours and speed of pattern change of Nassau groupers Epinephelus striatus at Little Cayman Island, British West Indies. Three basic camouflaged body patterns were observed under natural conditions and characterized quantitatively. The mean speed of pattern change across the entire body was 4.44 s (range = 0.97-9.87 s); the fastest pattern change as well as contrast change within a fixed pattern occurred within 1 s. Aside from apparent defensive camouflage, E. striatus used camouflage offensively to approach crustacean or fish prey, and three successful predation events were recorded. Although animal camouflage is a widespread tactic, dynamic camouflage is relatively uncommon and has been studied rarely in marine teleosts under natural conditions. The rapid changes observed in E. striatus suggest direct neural control of some skin colouration elements, and comparative studies of functional morphology and behaviour of colour change in other coral-reef teleosts are likely to reveal new mechanisms and adaptations of dynamic colouration.

Expression of squid iridescence depends on environmental luminance and peripheral ganglion control.

Squid display impressive changes in body coloration that are afforded by two types of dynamic skin elements: structural iridophores (which produce iridescence) and pigmented chromatophores. Both color elements are neurally controlled, but nothing is known about the iridescence circuit, or the environmental cues, that elicit iridescence expression. To tackle this knowledge gap, we performed denervation, electrical stimulation and behavioral experiments using the long-fin squid, Doryteuthis pealeii. We show that while the pigmentary and iridescence circuits originate in the brain, they are wired differently in the periphery: (1) the iridescence signals are routed through a peripheral center called the stellate ganglion and (2) the iridescence motor neurons likely originate within this ganglion (as revealed by nerve fluorescence dye fills). Cutting the inputs to the stellate ganglion that descend from the brain shifts highly reflective iridophores into a transparent state. Taken together, these findings suggest that although brain commands are necessary for expression of iridescence, integration with peripheral information in the stellate ganglion could modulate the final output. We also demonstrate that squid change their iridescence brightness in response to environmental luminance; such changes are robust but slow (minutes to hours). The squid's ability to alter its iridescence levels may improve camouflage under different lighting intensities.

Vertical visual features have a strong influence on cuttlefish camouflage.

Cuttlefish and other cephalopods use visual cues from their surroundings to adaptively change their body pattern for camouflage. Numerous previous experiments have demonstrated the influence of two-dimensional (2D) substrates (e.g., sand and gravel habitats) on camouflage, yet many marine habitats have varied three-dimensional (3D) structures among which cuttlefish camouflage from predators, including benthic predators that view cuttlefish horizontally against such 3D backgrounds. We conducted laboratory experiments, using Sepia officinalis, to test the relative influence of horizontal versus vertical visual cues on cuttlefish camouflage: 2D patterns on benthic substrates were tested versus 2D wall patterns and 3D objects with patterns. Specifically, we investigated the influence of (i) quantity and (ii) placement of high-contrast elements on a 3D object or a 2D wall, as well as (iii) the diameter and (iv) number of 3D objects with high-contrast elements on cuttlefish body pattern expression. Additionally, we tested the influence of high-contrast visual stimuli covering the entire 2D benthic substrate versus the entire 2D wall. In all experiments, visual cues presented in the vertical plane evoked the strongest body pattern response in cuttlefish. These experiments support field observations that, in some marine habitats, cuttlefish will respond to vertically oriented background features even when the preponderance of visual information in their field of view seems to be from the 2D surrounding substrate. Such choices highlight the selective decision-making that occurs in cephalopods with their adaptive camouflage capability.

Neural control of tuneable skin iridescence in squid.

Fast dynamic control of skin coloration is rare in the animal kingdom, whether it be pigmentary or structural. Iridescent structural coloration results when nanoscale structures disrupt incident light and selectively reflect specific colours. Unlike animals with fixed iridescent coloration (e.g. butterflies), squid iridophores (i.e. aggregations of iridescent cells in the skin) produce dynamically tuneable structural coloration, as exogenous application of acetylcholine (ACh) changes the colour and brightness output. Previous efforts to stimulate iridophores neurally or to identify the source of endogenous ACh were unsuccessful, leaving researchers to question the activation mechanism. We developed a novel neurophysiological preparation in the squid Doryteuthis pealeii and demonstrated that electrical stimulation of neurons in the skin shifts the spectral peak of the reflected light to shorter wavelengths (greater than 145 nm) and increases the peak reflectance (greater than 245%) of innervated iridophores. We show ACh is released within the iridophore layer and that extensive nerve branching is seen within the iridophore. The dynamic colour shift is significantly faster (17 s) than the peak reflectance increase (32 s), revealing two distinct mechanisms. Responses from a structurally altered preparation indicate that the reflectin protein condensation mechanism explains peak reflectance change, while an undiscovered mechanism causes the fast colour shift.

To be seen or to hide: visual characteristics of body patterns for camouflage and communication in the Australian giant cuttlefish Sepia apama.

It might seem obvious that a camouflaged animal must generally match its background whereas to be conspicuous an organism must differ from the background. However, the image parameters (or statistics) that evaluate the conspicuousness of patterns and textures are seldom well defined, and animal coloration patterns are rarely compared quantitatively with their respective backgrounds. Here we examine this issue in the Australian giant cuttlefish Sepia apama. We confine our analysis to the best-known and simplest image statistic, the correlation in intensity between neighboring pixels. Sepia apama can rapidly change their body patterns from assumed conspicuous signaling to assumed camouflage, thus providing an excellent and unique opportunity to investigate how such patterns differ in a single visual habitat. We describe the intensity variance and spatial frequency power spectra of these differing body patterns and compare these patterns with the backgrounds against which they are viewed. The measured image statistics of camouflaged animals closely resemble their backgrounds, while signaling animals differ significantly from their backgrounds. Our findings may provide the basis for a set of general rules for crypsis and signals. Furthermore, our methods may be widely applicable to the quantitative study of animal coloration.

Cephalopod dynamic camouflage: bridging the continuum between background matching and disruptive coloration.

Individual cuttlefish, octopus and squid have the versatile capability to use body patterns for background matching and disruptive coloration. We define--qualitatively and quantitatively--the chief characteristics of the three major body pattern types used for camouflage by cephalopods: uniform and mottle patterns for background matching, and disruptive patterns that primarily enhance disruptiveness but aid background matching as well. There is great variation within each of the three body pattern types, but by defining their chief characteristics we lay the groundwork to test camouflage concepts by correlating background statistics with those of the body pattern. We describe at least three ways in which background matching can be achieved in cephalopods. Disruptive patterns in cuttlefish possess all four of the basic components of 'disruptiveness', supporting Cott's hypotheses, and we provide field examples of disruptive coloration in which the body pattern contrast exceeds that of the immediate surrounds. Based upon laboratory testing as well as thousands of images of camouflaged cephalopods in the field (a sample is provided on a web archive), we note that size, contrast and edges of background objects are key visual cues that guide cephalopod camouflage patterning. Mottle and disruptive patterns are frequently mixed, suggesting that background matching and disruptive mechanisms are often used in the same pattern.

Modular organization of adaptive colouration in flounder and cuttlefish revealed by independent component analysis.

Flounders and cuttlefish have an impressive ability to change colouration, for camouflage and, in the case of cuttlefish, for communication. We pursue the hypothesis that these diverse patterns are created by combining a small number of distinct pattern modules. Independent component analysis (ICA) is a powerful tool for identifying independent sources of variation in linear mixtures of signals. Two versions of ICA are used, one assuming that sources have independence over time, and the other over space. These reveal the modularity of the skin colouration system, and suggest how the pattern modules are combined in specific behavioural contexts. ICA may therefore be a useful tool for studying animal camouflage and communication.

Cuttlefish camouflage: visual perception of size, contrast and number of white squares on artificial checkerboard substrata initiates disruptive coloration.

We investigated some visual background features that influence young cuttlefish, Sepia pharaonis, to change their skin patterning from 'general resemblance' of the substratum to disruptive coloration that breaks up their body form. Using computer-generated black/white checkerboard patterns as substrata, we first found that the size of the white squares had to be within a certain narrow range (relative to the size of the cuttlefish 'white square') for the animal to exhibit disruptive skin patterning. Second, given the appropriate size of checker, cuttlefish regulated their disruptive skin patterns according to the contrast between white and black squares. Third, by manipulating the number of white squares on a black background, we found that as few as four white squares among 316 black squares (or 1.25%) produced disruptive patterning, yet increasing the number of white squares to 20, 40 or 80 did not increase the frequency of appearance of the cuttlefish 'white square', but only its clarity of expression. These results demonstrate that the size, contrast and number of white objects in the surrounding substratum influence the production and expression of disruptive skin patterns in young cuttlefish.

Experimental evidence for spatial learning on octopuses (octopus bimaculoides).

Octopuses forage far from temporary home dens to which they return for shelter. Spatial tasks may assess learning. Octopuses (Octopus bimaculoides) were placed in a novel arena, and their movements were tracked for 72 hr. Movements around the arena decreased across time, consistent with exploratory learning. Next, octopuses were given 23 hr to move around an arena; after a 24-hr delay, their memory of a burrow location was tested. Most remembered the location of the open burrow, demonstrating learning in 1 day. Finally, octopuses were trained to locate a single open escape burrow among 6 possible locations. Retention was tested after a week and was immediately followed by reversal training (location rotated 180 degrees ). Octopuses learned the original location of the burrow, remembering it for a week. Path lengths increased significantly after reversal, gradually improving and showing relearning. Octopuses show exploratory behavior, learning, and retention of spatial information.

Cuttlefish use polarization sensitivity in predation on silvery fish.

Cephalopods are sensitive to the linear polarization characteristics of light. To examine if this polarization sensitivity plays a role in the predatory behavior of cuttlefish, we examined the preference of Sepia officinalis when presented with fish whose polarization reflection was greatly reduced versus fish whose polarization reflection was not affected. Cuttlefish preyed preferably on fish with normal polarization reflection over fish that did not reflect linearly polarized light (n = 24, chi 2 = 17.3, P < 0.0001), implying that polarization sensitivity is used during predation. We suggest that polarization vision is used to break the countershading camouflage of light-reflecting silvery fish.

Three-dimensional odor tracking by Nautilus pompilius.

The 'living fossil' Nautilus pompilius is thought to use olfaction as its primary sensory system during foraging, yet neither the organs responsible for olfaction nor the mechanisms or behaviors associated with odor tracking have been subjected to experimentation. Flume testing under dark conditions revealed that Nautilus could consistently detect and follow turbulent odor plumes to the source over distances up to 10 m, exhibiting two types of orientation behavior while sampling in three dimensions. The paired rhinophores were necessary for orientation behavior: when they were temporarily blocked either uni- or bilaterally, Nautilus detected odor but could not track the plume and locate the source. Animals that were tested post-blockage were able to track and locate the source. The role of the 90 thin tentacles remains enigmatic; they seemed to be able to detect odor, but they were not capable of guiding orientation behavior towards a distant odor source. Bilateral chemical sensing by rhinophores in three dimensions may have been the Umwelt of ammonites and belemnites before the evolution of complex eyes and fast locomotion in modern coleoids.

Pattern of inheritance of microsatellite loci in the squid Loligo pealeii (Mollusca: Cephalopoda).

Six microsatellite loci are described for the squid Loligo pealeii. All loci exhibit some degree of allelic diversity. The pattern of inheritance was tested for 3 loci through an analysis of the filial genotypes from a female-male mating. At all 3 loci, the ratios of the filial genotypes conformed to the ratios expected by Mendelian inheritance. The hypervariable loci will be useful in studies on sexual selection in this species, whereas the relatively less variable loci will be useful to address questions of population structure.

Observational learning does not explain improvement in predation tactics by cuttlefish (Mollusca: Cephalopoda).

When first presented with live crab prey, naive cuttlefish typically approached from the front and were often pinched. In subsequent trials, this initial group rapidly improved their prey capture techniques and attacked from above or behind the crab. Naive cuttlefish that first watched experienced conspecifics prey on crabs captured crabs without getting pinched. However, naive cuttlefish that first watched non-attacking cuttlefish in the same tank with crabs also avoided pinches, as did naive cuttlefish that were exposed only to crab odor. All three experimental groups were as successful on their first predation as the initial group was on its second predation, but the attack techniques they used were not as well developed as those of the initial group on their fifth trial. Results suggest that odor may serve as a primer for cuttlefish predatory attack behavior, perhaps by enhancing food arousal and improving attention. Practice was required for further improvements in predation techniques. We found no evidence that cuttlefish improved their predation techniques by observing conspecifics.