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.     

A preliminary analysis of sleep-like states in the cuttlefish Sepia officinalis

Sleep has been observed in several invertebrate species, but its presence in marine invertebrates is relatively unexplored. Rapid-eye-movement (REM) sleep has only been observed in vertebrates. We investigated whether the cuttlefish Sepia officinalis displays sleep-like states. We find that cuttlefish exhibit frequent quiescent periods that are homeostatically regulated, satisfying two criteria for sleep. In addition, cuttlefish transiently display a quiescent state with rapid eye movements, changes in body coloration and twitching of the arms, that is possibly analogous to REM sleep. Our findings thus suggest that at least two different sleep-like states may exist in Sepia officinalis.     

Food imprinting, new evidence from the cuttlefish Sepia officinalis

Imprinting provides precocial offspring with an efficient means to optimize their subsequent behaviours. We discovered food imprinting using a sophisticated invertebrate model: the cuttlefish. We showed that early juveniles preferred the prey to which they have been visually familiarized, when the amount of information was sufficient and only if such familiarization occurred during a short sensitive period. We also demonstrated that the effects of visual food imprinting overcame those of the first food ingested. Our study shows that visual imprinting is a critical process in animals, surpassing more direct reward experiences that occur outside the critical exposure period.     

Small-scale rearing of cuttlefish (Sepia officinalis) for research purposes

We report a methodology refined over 20 years to culture and maintain a small colony of Sepia officinalis for research year-round. Wild-caught eggs were obtained annually from England and reared in semi-closed natural seawater systems of large volume. Constant temperature (15 °C) and day length (12L/12D) delayed sexual maturation and reproductive behavior. This extended life cycle by roughly 50%, thus providing small research animals for about 18 months from every annual batch of eggs. A novel live food – gammarid crustaceans collected from washed up seagrass– was provided to hatchlings and juveniles. Juveniles were then trained to take thawed shrimp thereafter, thus reducing the expense of live foods. Typical survival to one year was >65%. With these methods, healthy sexually immature cuttlefish were available year-round for behavioral and physiological studies without the confounding influences of hormonally-induced fighting, mating, and egg laying that typically occur within six months.     

Effects of early visual experience on the background preference in juvenile cuttlefish Sepia pharaonis

Although cuttlefish are capable of showing diverse camouflage body patterns against a variety of background substrates, whether they show background preference when given a choice of substrates is not well known. In this study, we characterized the background choice of post-embryonic cuttlefish (Sepia pharaonis) and examined the effects of rearing visual environments on their background preferences. Different rearing backgrounds (enriched, uniformly grey and checkerboard) were used to raise cuttlefish from eggs or hatchlings, and four sets of two-background-choice experiments (differences in contrast, shape, size and side) were conducted at day 1 and weeks 4, 8 and 12 post-hatch. Cuttlefish reared in the enriched environment preferred high-contrast backgrounds at all post-embryonic stages. In comparison, those reared in the impoverished environments (uniformly grey and checkerboard) had either reversed or delayed high-contrast background preference. In addition, cuttlefish raised on the uniformly grey background, exposed to a checkerboard briefly (0.5 or 3 h) at week 4 and tested at week 8 showed increased high-contrast background preference. Interestingly, cuttlefish in the enriched group preferred an object size similar to their body size at day 1 and week 4, but changed this preference to smaller objects at week 12. These results suggest that high-contrast backgrounds may be more adaptive for juvenile cuttlefish, and visually enriched environments are important for the development of these background preference behaviours.     

Effects of temperature on the growth and microstructure formation of cuttlebone from cuttlefish Sepia pharaonis

ABSTRACT

This study investigated the effects of three temperatures (20°C, 27°C, and 31°C) on the physiological performance (survival and growth) and cuttlebone micromorphological features (chamber number, chamber height and lamellae number) of cuttlefish Sepia pharaonis. We examined gross morphological characteristics of the internal calcareous cuttlebone to determine whether lamellar matrix was impacted by temperature. Juvenile survival was significantly affected by temperature (χ²?=?54.580, df?=?2, P?<?0.001). Cuttlebone weight, length and width were also positively correlated with temperature. Scanning electron microscopy revealed that a single chamber structure consists of septa, lamellae and pillars. At 20°C the chamber number of 89.0?±?10.8 was significantly higher than at 27°C with 44.8?±?3.6 or 31°C with 47.5?±?4.3 (Kruskal–Wallis [KW], χ^2?=?26.391, df?=?2, P?=?0.0001), whilst chamber height was lower at 20°C (KW χ^2?=?27.842, df?=?2, P?=?0.0001). Moreover, lamellae number varied among the treatments (KW χ^2?=?22.411, df?=?2, P?=?0.0002). Lamellae numbers at 20°C, 27°C and 31°C were 3–6, 6–9 and 5–8, respectively. The results indicated that the intrinsic lamellar matrix structure was significantly affected by temperature and that this effect may be used in cuttlebone growth studies.     

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.     

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.     

Behavioural responses of juvenile cuttlefish (Sepia officinalis) to local water movements

Physiological studies have shown that the epidermal head and arm lines in cephalopods are a mechanoreceptive system that is similar to the fish and amphibian lateral lines (Budelmann BU, Bleckmann H. 1988. A lateral line analogue in cephalopods: Water waves generate microphonic potentials in the epidermal head lines of Sepia officinalis and Lolliguncula brevis. J. Comp. Physiol. A 164:1-5.); however, the biological significance of the epidermal lines remains unclear. To test whether cuttlefish show behavioural responses to local water movements, juvenile Sepia officinalis were exposed to local sinusoidal water movements of different frequencies (0.01-1000 Hz) produced by a vibrating sphere. Five behavioural responses were recorded: body pattern changing, moving, burrowing, orienting, and swimming. Cuttlefish responded to a wide range of frequencies (20-600 Hz), but not to all of the frequencies tested within that range. No habituation to repeated stimuli was seen. Results indicate that cuttlefish can detect local water movements (most likely with the epidermal head and arm lines) and are able to integrate that information into behavioural responses.     

Acetylcholine release and choline uptake by cuttlefish (Sepia officinalis) optic lobe synaptosomes

Acetylcholine (ACh), which is synthesized from choline (Ch), is believed to hold a central place in signaling mechanisms within the central nervous system (CNS) of cuttlefish (Sepia officinalis) and other coleoid cephalopods. Although the main elements required for cholinergic function have been identified in cephalopods, the transmembrane translocation events promoting the release of ACh and the uptake of Ch remain largely unsolved. The ACh release and Ch uptake were quantitatively studied through the use of in vitro chemiluminescence and isotopic methods on a subcellular fraction enriched in synaptic nerve endings (synaptosomes) isolated from cuttlefish optic lobe. The ACh release evoked by K+ depolarization was found to be very high (0.04 pmol ACh.s(-1).mg(-1) protein). In response to stimulation by veratridine, a secretagogue (a substance that induces secretion) that targets voltage-gated Na+ channels, the release rate and the total amount of ACh released were significantly lower, by 10-fold, than the response induced by KCl. The high-affinity uptake of choline was also very high (31 pmol Ch.min(-1).mg(-1) protein). The observed ACh release and Ch uptake patterns are in good agreement with published data on preparations characterized by high levels of ACh metabolism, adding further evidence that ACh acts as a neurotransmitter in cuttlefish optic lobe.     

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.     

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.     

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.     

Functional response of early stages of the cuttlefish Sepia officinalis preying on the mysid Mesopodopsis slabberi

The functional response of Sepia officinalis early stages, preying on mysids of the species Mesopodopsis slabberi was investigated. The effects of five prey densities (12.5, 25, 37.5, 50 and 125 mysids l^-1) and two hatchling ages (1-day-old and 7-day-old) on consumption rate and the frequency of non-feeding animals were tested. Older animals were approximately 50% heavier than newly hatched ones. Hatchlings were individually assayed under 0.25 W m^-2 natural light, 37.8 psu in salinity and 19°C. The effect of prey density on consumption rate was highly significant and no effect of age was detected within the age range tested. Maximal values recorded for consumption rate were about 0.45 mysids h^-1. The frequency of non-feeding individuals was strongly reduced at saturating prey densities. The functional response curve showed an interval of prey densities for which density-dependent prey mortality is probable.     

Quantification of cuttlefish (Sepia officinalis) camouflage: a study of color and luminance using in situ spectrometry

Cephalopods are renowned for their ability to adaptively camouflage on diverse backgrounds. Sepia officinalis camouflage body patterns have been characterized spectrally in the laboratory but not in the field due to the challenges of dynamic natural light fields and the difficulty of using spectrophotometric instruments underwater. To assess cuttlefish color match in their natural habitats, we studied the spectral properties of S. officinalis and their backgrounds on the Aegean coast of Turkey using point-by-point in situ spectrometry. Fifteen spectrometry datasets were collected from seven cuttlefish; radiance spectra from animal body components and surrounding substrates were measured at depths shallower than 5 m. We quantified luminance and color contrast of cuttlefish components and background substrates in the eyes of hypothetical di- and trichromatic fish predators. Additionally, we converted radiance spectra to sRGB color space to simulate their in situ appearance to a human observer. Within the range of natural colors at our study site, cuttlefish closely matched the substrate spectra in a variety of body patterns. Theoretical calculations showed that this effect might be more pronounced at greater depths. We also showed that a non-biological method (“Spectral Angle Mapper”), commonly used for spectral shape similarity assessment in the field of remote sensing, shows moderate correlation to biological measures of color contrast. This performance is comparable to that of a traditional measure of spectral shape similarity, hue and chroma. This study is among the first to quantify color matching of camouflaged cuttlefish in the wild.