Symmetrical crypsis and asymmetrical signalling in the cuttlefish Sepia officinalis

The salience of bilateral symmetry to humans has led to the suggestion that camouflage may be enhanced in asymmetrical patterns. However, the importance of bilateral symmetry in visual signals (and overall morphology) may constrain the evolution of asymmetrical camouflage, resulting in the bilaterally symmetrical cryptic patterns that we see throughout the animal kingdom. This study investigates the cuttlefish (Sepia officinalis), which can control the degree of symmetry in its coloration. Ten juvenile S. officinalis were filmed in two behavioural contexts (cryptic and threatened) to test the prediction that cryptic patterns will be expressed more asymmetrically than an anti-predator signal known as the 'deimatic display'. Cryptic body patterns, particularly those with a disruptive function, were found to exhibit a high degree of bilateral symmetry. By contrast, the components of the deimatic display were often expressed asymmetrically. These results are contrary to the predicted use of symmetry in defensive coloration, indicating that the role of symmetry in both crypsis and visual signalling is not as straightforward as previously suggested.     

Visual interpolation for contour completion by the European cuttlefish (Sepia officinalis) and its use in dynamic camouflage

Cuttlefish rapidly change their appearance in order to camouflage on a given background in response to visual parameters, giving us access to their visual perception. Recently, it was shown that isolated edge information is sufficient to elicit a body pattern very similar to that used when a whole object is present. Here, we examined contour completion in cuttlefish by assaying body pattern responses to artificial backgrounds of 'objects' formed from fragmented circles, these same fragments rotated on their axis, and with the fragments scattered over the background, as well as positive (full circles) and negative (homogenous background) controls. The animals displayed similar responses to the full and fragmented circles, but used a different body pattern in response to the rotated and scattered fragments. This suggests that they completed the broken circles and recognized them as whole objects, whereas rotated and scattered fragments were instead interpreted as small, individual objects in their own right. We discuss our findings in the context of achieving accurate camouflage in the benthic shallow-water environment.     

Perception of visual texture and the expression of disruptive camouflage by the cuttlefish, Sepia officinalis

Juvenile cuttlefish (Sepia officinalis) camouflage themselves by changing their body pattern according to the background. This behaviour can be used to investigate visual perception in these molluscs and may also give insight into camouflage design. Edge detection is an important aspect of vision, and here we compare the body patterns that cuttlefish produced in response to checkerboard backgrounds with responses to backgrounds that have the same spatial frequency power spectrum as the checkerboards, but randomized spatial phase. For humans, phase randomization removes visual edges. To describe the cuttlefish body patterns, we scored the level of expression of 20 separate pattern 'components', and then derived principal components (PCs) from these scores. After varimax rotation, the first component (PC1) corresponded closely to the so-called disruptive body pattern, and the second (PC2) to the mottle pattern. PC1 was predominantly expressed on checkerboards, and PC2 on phase-randomized backgrounds. Thus, cuttlefish probably have edge detectors that control the expression of disruptive pattern. Although the experiments used unnatural backgrounds, it seems probable that cuttlefish display disruptive camouflage when there are edges in the visual background caused by discrete objects such as pebbles. We discuss the implications of these findings for our understanding of disruptive camouflage.     

Role of blood-oxygen transport in thermal tolerance of the cuttlefish, Sepia officinalis

Mechanisms that affect thermal tolerance of ectothermic organismshave recently received much interest, mainly due to global warmingand climate-change debates in both the public and in the scientificcommunity. In physiological terms, thermal tolerance of severalmarine ectothermic taxa can be linked to oxygen availability,with capacity limitations in ventilatory and circulatory systemscontributing to oxygen limitation at extreme temperatures. Thepresent review briefly summarizes the processes that definethermal tolerance in a model cephalopod organism, the cuttlefishSepia officinalis, with a focus on the contribution of the cephalopodoxygen-carrying blood pigment, hemocyanin. When acutely exposedto either extremely high or low temperatures, cuttlefish displaya gradual transition to an anaerobic mode of energy productionin key muscle tissues once critical temperatures (T_crit) arereached. At high temperatures, stagnating metabolic rates anda developing hypoxemia can be correlated with a progressivefailure of the circulatory system, well before T_crit is reached.However, at low temperatures, declining metabolic rates cannotbe related to ventilatory or circulatory failure. Rather, wepropose a role for hemocyanin functional characteristics asa major limiting factor preventing proper tissue oxygenation.Using information on the oxygen binding characteristics of cephalopodhemocyanins, we argue that high oxygen affinities (= low P₅₀values), as found at low temperatures, allow efficient oxygenshuttling only at very low venous oxygen partial pressures.Low venous PO₂s limit rates of oxygen diffusion into cells,thus eventually causing the observed transition to anaerobicmetabolism. On the basis of existing blood physiological, molecular,and crystallographical data, the potential to resolve the roleof hemocyanin isoforms in thermal adaptation by an integratedmolecular physiological approach is discussed.     

Perception of edges and visual texture in the camouflage of the common cuttlefish, Sepia officinalis

The cuttlefish, Sepia officinalis, provides a fascinating opportunity to investigate the mechanisms of camouflage as it rapidly changes its body patterns in response to the visual environment. We investigated how edge information determines camouflage responses through the use of spatially high-pass filtered 'objects' and of isolated edges. We then investigated how the body pattern responds to objects defined by texture (second-order information) compared with those defined by luminance. We found that (i) edge information alone is sufficient to elicit the body pattern known as Disruptive, which is the camouflage response given when a whole object is present, and furthermore, isolated edges cause the same response; and (ii) cuttlefish can distinguish and respond to objects of the same mean luminance as the background. These observations emphasize the importance of discrete objects (bounded by edges) in the cuttlefish's choice of camouflage, and more generally imply that figure-ground segregation by cuttlefish is similar to that in vertebrates, as might be predicted by their need to produce effective camouflage against vertebrate predators.     

Cytobiological studies on hemocyanin metabolism in the branchial heart complex of the common cuttlefish Sepia officinalis (Cephalopoda, Dibranchiata)

The present study confirms previous investigations that demonstrated a high copper content in the branchial heart and its appendage, and that gave the first indication that this organ complex might be involved in hemocyanin metabolism in Sepia officinalis L. Immunocytochemical localization of hemocyanin molecules within the endocytotic lysosomal system of the ovoid cells and tracer experiments with ¹²⁵I-labeled Sepia hemocyanin suggest its endocytotic uptake. Energy-dispersive X-ray microanalysis and histochemical methods reveal a high copper content within the ovoid cells of the branchial heart. In view of the turnover of the respiratory pigment in the branchial heart of Sepia officinalis L., we believe that the ovoid cells are a site of hemocyanin catabolism.     

Identification and expression of two oxytocin/vasopressin-related peptides in the cuttlefish Sepia officinalis

Two novel members of the oxytocin/vasopressin superfamily have been identified in the cephalopod Sepia officinalis. Oxytocin/vasopressin gene sequences were cloned by Race PCR. The two precursors we identified exhibit the classical organization of OT/VP superfamily precursors: a signal peptide followed by a nonapeptide and a neurophysin domain. The neurophysin domain is entirely conserved for the cuttlefish precursors, but the nonapeptides and the signal peptides differ. The first nonapeptide, called sepiatocin, is highly homologous to Octopus vulgaris octopressin. The second nonapeptide, called pro-sepiatocin, shows sequence homologies with a Crustacean oxytocin/vasopressin-like peptide identified in Daphnia culex and with a novel form of oxytocin described in New World monkeys. The expression of pro-sepiatocin is restricted to the supraesophageal and subesophageal masses of the brain whereas sepiatocin is expressed in the entire central nervous system. Sepiatocin, as described for octopressin, modulates the contractile activity of several muscles such as penis, oviduct and vena cava muscles; this suggests its involvement in reproduction and blood circulation. Pro-sepiatocin is released in the hemolymph; it is a neurohormone able to target numerous peripheral organs.     

Central distribution and three-dimensional arrangement of fin chromatophore motoneurons in the cuttlefish Sepia officinalis

Cephalopod body patterning is a most complex invertebrate behavior. Generated primarily by pigment-containing chromatophore organs, this behavior enables rapid alteration of body coloration as a result of direct innervation of chromatophores by motoneurons. This study focuses on location and arrangement of fin chromatophore motoneurons in the cuttlefish Sepia and investigates the possibility of central topography. Retrograde labeling of topographically arranged fin nerve branches in the periphery revealed the posterior subesophageal mass (PSEM) of the brain as the primary location of fin chromatophore motoneurons; within this region, most cells were located in the posterior chromatophore and fin lobes. Additionally, a small percentage of labeled motoneurons occurred in the anterior subesophageal mass and the stellate ganglia. Data from three-dimensional reconstructions of PSEMs showed the arrangement of labeled motoneurons within individual lobes; these data suggest no obvious topographic arrangement. Further, electrical stimulation of the PSEM generated chromatophore activity on the fin and mantle. These stimulation results, coupled with the retrograde labeling, suggest that chromatophore motoneurons are located across multiple PSEM lobes.     

Motor and behavioural effects induced by putative neurotransmitter injection into the optic lobe of the cuttlefish, Sepia officinalis

This paper presents a technique using local injections of different drugs directly into the optic lobe of Sepia. The cholinomimetic drugs induce a general decrease of the motricity, muscle tone, frequency of respiratory movements and decoloration of the animal. Dopamine and noradrenaline produce the same complex motor effects obtained by chronic electrical stimulation. Serotonin induces complex effects, particularly on the coloration. Some serotoninergic synapses could be implicated in the triggering of colour patterns.     

Microstructural and histochemical advances on the digestive gland of the common cuttlefish,Sepia officinalis L.

The cephalopod digestive gland is a complex organ that, although analogous to the vertebrate liver, has additional functions, with special (albeit not exclusive) note on its active role in digestion. Although the structure of the digestive cell and its main constituents are well known (among which “boules” and brown bodies are distinctive features), histological details of other cell types and the general structure of the digestive gland need still further research. By a thorough combination of histological and histochemical techniques, it is shown that the digestive gland diverticula of the common cuttlefish (Sepia officinalis L.) are comprised of three essential cell types: digestive, basal and excretory. Basal (“pyramidal”) cells are multi-functional, being responsible for cell replacement and detoxification, mainly through the production of calcic spherulae containing metals like copper and lead in a complex organic matrix of proteins and ribonucleins. Since copper- and lead-positive spherulae were almost absent from other cell types and lumen of the tubules, it appears that controlled bioaccumulation of these metals, rather than excretion, is the main detoxification mechanism. The results show that the organ is crossed by an intricate network of blood vessels, especially arteries and arterioles, whose contents share histochemical properties with a particular set of “boules” that are shed into the lumen of diverticula for elimination, suggesting that the organ actively removes unwanted metabolites from the haemolymph. Conversely, the rarer excretory cells appear to be specialized in the elimination of salts. Although the exact nature of many excretory and secretory products, as the metabolic pathways that originate them, remain elusive, the findings suggest an intricate interaction between the different cell types and between these and the surrounding media: haemolymph and digestive tract.     

Identification of SepCRP analogues in the cuttlefish Sepia officinalis: a novel family of ovarian regulatory peptides

In the cuttlefish, Sepia officinalis, the ovary appears to be one of the main sources of regulatory peptides involved in the successive steps of egg-laying. Following the identification of the SepCRP-1, which is a peptide extracted from ovary and involved in egg capsule secretion, investigations were focused on the identification of related peptides. Seven related-Sepia Capsule Releasing Peptides (R-SepCRPs) were identified by means of mass spectrometry and characterized using MS/MS spectra and/or Edman degradation. Finally, primary structures were verified by the comparison of MS/MS spectra from endogenic and synthetic peptides. This new ovarian peptide family exhibits a conserved SLXKD tag involved in the biological activity. LC-MS/MS screening clearly demonstrates that R-SepCRPs are restricted to the female genital tract. Expressed during vitellogenesis, they are released by vitellogenic follicles and full-grown oocytes (FGO) in the genital coelom. Biological activities suggest that R-SepCRPs would be responsible for the storage of FGO before mating and would take part in the mechanical secretion of egg capsule products, as previously described for SepCRP-1.     

Components of the cellular defense and detoxification system of the common cuttlefish Sepia officinalis (Mollusca,Cephalopoda)

Endocytotic-active cells in the branchial heart complex of Sepia officinalis were studied by in situ injection of different types of xenobiotics and by in vitro perfusion of the organ complex with a bacterial suspension. The rhogocytes (ovoid cells) ingest particles of all tested sizes by endocytosis and phagocytosis. The hemocytes of the circulating blood and the adhesive hemocytes in the wall of the branchial heart incorporate all tested kinds of foreign materials, including bacterial cells due to phagocytosis achieved by the triangular mesenchymatic cells. The ultrastructural findings also give strong evidence that the triangular mesenchymatic cells are fixed hemocytes that have migrated into the branchial heart tissue. The ingestion and digestion of allogeneic substances and bacteria or their debris by rhogocytes and/or all (forms of) hemocytes suggests the involvement of these either fixed or mobile endocytotic-active cells in the defense and detoxification system of cephalopods.     

Nitric oxide synthase in the nervous system and ink gland of the cuttlefish Sepia officinalis: molecular cloning and expression

Nitric oxide (NO) signaling is involved in numerous physiological processes in mollusks, e.g., learning and memory, feeding behavior, neural development, and defence response. We report the first molecular cloning of NOS mRNA from a cephalopod, the cuttlefish Sepia officinalis (SoNOS). SoNOS was cloned using a strategy that involves hybridization of degenerate PCR primers to highly conserved NOS regions, combined with RACE procedure. Two splicing variants of SoNOS, differing by 18 nucleotides, were found in the nervous system and the ink gland of Sepia. In situ hybridization shows that SoNOS is expressed in the immature and mature cells of the ink gland and in the regions of the nervous system that are related to the ink defence system.     

Localization of an extracerebral NSV-ganglion in the cephalopod, Sepia officinalis

The neurosecretory system of the vena cava (NSV) of Sepia officinalis contacts the palliovisceral lobe with some axons that run parallel to the visceral nerves. Distal to the palliovisceral lobe the NSV- system widens to form a hitherto unknown extracerebral ganglion containing approximately 4200 perikarya. This is regarded as the primary origin of neurotransmitters. Distal to this nucleus area the volume and the number of cell bodies in the NSV-system is reduced. It contains neurosecretory nerve cells, two glial cell types, large cell accumulations, connective tissue and capillaries. Histochemical, immunohisto- and immunocytochemical examinations show the existence of catecholamines, and the coexistence of serotonin and FMRFamide in the NSV-System. A HPLC analysis differentiated between dopamine, noradrenaline, and adrenaline.     

Behavioral laterality and morphological asymmetry in the cuttlefish, Sepia lycidas

Behavioral laterality is widely found among vertebrates, but has been little studied in aquatic invertebrates. We examined behavioral laterality in attacks on prey shrimp by the cuttlefish, Sepia lycidas, and correlated this to their morphological asymmetry. Behavioral tests in the laboratory revealed significant individual bias for turning either clockwise or counterclockwise toward prey, suggesting behavioral dimorphism in foraging behavior. Morphological bias was examined by measuring the curvature of the cuttlebone; in some the cuttlebone was convex to the right (righty), while in others, the cuttlebone was convex to the left (lefty). The frequency distributions of an index of cuttlebone asymmetry were bimodal, indicating that populations were composed of two types of individuals: "righty" and "lefty." Moreover, an individual's laterality in foraging behavior corresponded with the asymmetry of its cuttlebone, with righty individuals tending to turn counterclockwise and lefty ones in the opposite direction. These results indicate that cuttlefish exhibit behavioral dimorphism and morphological antisymmetry in natural populations. The presence of two types of lateral morph in cuttlefish provides new information on the relationship between antisymmetric morphologies and the evolution of individual laterality in behavioral responses in cephalopods. The implications of these findings for the interpretation of ecological meaning and maintenance mechanisms of laterality in cuttlefish are also discussed.