Oval Squid Sepioteuthis Lessoniana Research Articles

Squid adjust their body color according to substrate

Coleoid cephalopods camouflage on timescales of seconds to match their visual surroundings. To date, studies of cephalopod camouflage-to-substrate have been focused primarily on benthic cuttlefish and octopus, because they are readily found sitting on the substrate. In contrast to benthic cephalopods, oval squid (Sepioteuthis lessoniana species complex) are semi-pelagic animals that spend most of their time in the water column. In this study, we demonstrate that in captivity, S. lessoniana Sp.2 (Shiro-ika, white-squid) from the Okinawa archipelago, Japan, adapts the coloration of their skin using their chromatophores according to the background substrate. We show that if the animal moves between substrates of different reflectivity, the body patterning is changed to match. Chromatophore matching to substrate has not been reported in any loliginid cephalopod under laboratory conditions. Adaptation of the chromatophore system to the bottom substrate in the laboratory is a novel experimental finding that establishes oval squid as laboratory model animals for further research on camouflage.

Allometry for Eyes and Optic Lobes in Oval Squid (Sepioteuthis lessoniana) with Special Reference to Their Ontogenetic Asymmetry

Eyes develop in relation to body size and brain area for visual processing in some vertebrates. Meanwhile, it is well known that many animals exhibit left–right asymmetry in both morphology and behavior, namely, lateralization. However, it remains unclear whether the eyes and visual processing brain areas synchronously develop for their asymmetry. Oval squid (Sepioteuthis lessoniana) exhibits lateralization of optic lobe volume and left or right eye usage toward specific targets during their ontogeny. We address the question of how left–right asymmetry of the eyes and optic lobes exhibit an allometric pattern. To examine this question, we estimated the left and right volumes of eyes and optic lobes using microcomputed tomography. We found that, for the optic lobe volume, the right enlargement that appeared at ages 45 and 80 days then shifted to the left at age 120 days. In contrast, the volume of eyes did not show any left–right asymmetries from hatching to age 120 days. We also found that the volume of the eyes and optic lobes showed a slower increase than that of the whole-body size. Within these two visually related organs, the eyes grew faster than the optic lobes until age 120 days. These results are discussed in the context of the survival strategy of oval squid that form schools, two months post-hatching.

The overlapping reproductive traits of the two male mating types of the oval squid Sepioteuthis lessoniana

The oval squid Sepioteuthis lessoniana is polyandrous, and a female mates with several males during a spawning season. This has resulted in two alternative male mating tactics in this species. The larger consort males usually use the male-parallel (MP) mating posture to put spermatophores at the opening of the oviduct; the smaller sneaker males predominantly use the male-upturned (MU) mating posture to place spermatophores around the female’s buccal membrane. Since squid eggs are released from the oviduct, MP mating is expected to have a higher fertilization rate than MU mating. Given the fact that these two male mating tactics are largely dependent on the body size of the male relative to the female, it is unclear how the smaller males are able to reproductively compete with the larger males. On analyzing spermatophore and sperm morphology from populations of adult male squids, spermatophore size was found to be positively correlated with mantle length of these squids, but sperm length was negatively correlated with squid mantle length. More importantly, no distinct size dimorphism exists in relation to either spermatophore morphology or sperm morphology. The overlap in size distributions of the spermatophores and sperms of the male squid thus implies that medium-sized males may have flexible reproductive strategies, switching between MP and MU mating tactics depending on the context of the mating event and/or female choice. This presumed behavioral plasticity might increase the reproductive success of these males and maintain the dynamic stability of two alternative mating types in this polyandrous species.

Morphological changes of the optic lobe from late embryonic to adult stages in oval squids Sepioteuthis lessoniana.

The optic lobe is the largest brain area within the central nervous system of cephalopods and it plays important roles in the processing of visual information, the regulation of body patterning, and locomotive behavior. The oval squid Sepioteuthis lessoniana has relatively large optic lobes that are responsible for visual communication via dynamic body patterning. It has been observed that the visual behaviors of oval squids change as the animals mature, yet little is known about how the structure of the optic lobes changes during development. The aim of the present study was to characterize the ontogenetic changes in neural organization of the optic lobes of S. lessoniana from late embryonic stage to adulthood. Magnetic resonance imaging and micro-CT scans were acquired to reconstruct the 3D-structure of the optic lobes and examine the external morphology at different developmental stages. In addition, optic lobe slices with nuclear staining were used to reveal changes in the internal morphology throughout development. As oval squids mature, the proportion of the brain making up the optic lobes increases continuously, and the optic lobes appear to have a prominent dent on the ventrolateral side. Inside the optic lobe, the cortex and the medulla expand steadily from the late embryonic stage to adulthood, but the cell islands in the tangential zone of the optic lobe decrease continuously in parallel. Interestingly, the size of the nuclei of cells within the medulla of the optic lobe increases throughout development. These findings suggest that the optic lobe undergoes continuous external morphological change and internal neural reorganization throughout the oval squid's development. These morphological changes in the optic lobe are likely to be responsible for changes in the visuomotor behavior of oval squids from hatching to adulthood.

Mismatch between the eye and the optic lobe in the giant squid.

Giant squids (Architeuthis) are a legendary species among the cephalopods. They live in the deep sea and are well known for their enormous body and giant eyes. It has been suggested that their giant eyes are not adapted for the detection of either mates or prey at distance, but rather are best suited for monitoring very large predators, such as sperm whales, at distances exceeding 120 m and at a depth below 600 m (Nilsson et al. 2012 Curr. Biol. 22, 683–688. (doi:10.1016/j.cub.2012.02.031)). However, it is not clear how the brain of giant squids processes visual information. In this study, the optic lobe of a giant squid (Architeuthis dux, male, mantle length 89 cm), which was caught by local fishermen off the northeastern coast of Taiwan, was scanned using high-resolution magnetic resonance imaging in order to examine its internal structure. It was evident that the volume ratio of the optic lobe to the eye in the giant squid is much smaller than that in the oval squid (Sepioteuthis lessoniana) and the cuttlefish (Sepia pharaonis). Furthermore, the cell density in the cortex of the optic lobe is significantly higher in the giant squid than in oval squids and cuttlefish, with the relative thickness of the cortex being much larger in Architeuthis optic lobe than in cuttlefish. This indicates that the relative size of the medulla of the optic lobe in the giant squid is disproportionally smaller compared with these two cephalopod species. This morphological study of the giant squid brain, though limited only to the optic lobe, provides the first evidence to support that the optic lobe cortex, the visual information processing area in cephalopods, is well developed in the giant squid. In comparison, the optic lobe medulla, the visuomotor integration centre in cephalopods, is much less developed in the giant squid than other species. This finding suggests that, despite the giant eye and a full-fledged cortex within the optic lobe, the brain of giant squids has not evolved proportionally in terms of performing complex tasks compared with shallow-water cephalopod species.

Quantitative Analysis of Dynamic Body Patterning Reveals the Grammar of Visual Signals during the Reproductive Behavior of the Oval Squid Sepioteuthis lessoniana

Cephalopods use a diverse range of body patterns for visual communication. Each pattern is composed of several distinct chromatic components that are under neural control and are expressed dynamically. In the oval squid Sepioteuthis lessoniana, males use distinct body patterns to interact with females and other males at the spawning site. To systematically examine their visual signals during reproductive behavior, an ethogram of 27 body pattern components produced by S. lessoniana was observed in both the wild and captivity; these were then characterized. Five behaviors were commonly seen among these reproductively active squids, namely parallel swimming, male guarding, male-male fighting, male-parallel mating, and male-upturn mating. Each behavior was found to be composed of the expression in a temporal sequence of different chromatic components. By analyzing the dynamic body patterning time series associated with each behavior, it was found that a certain subset of components was expressed simultaneously or sequentially in response to conspecifics. Importantly, the results not only revealed that each behavior is composed of multiple chromatic components, but the findings also showed that each component is often associated with multiple behaviors. To gain insight into the visual communication associated with each behavior in terms of the body patterning's key components, the co-expression frequencies of two or more components at any moment in time were calculated in order to assess uniqueness when distinguishing one behavior from another. This approach identified the minimum set of key components that, when expressed together, represents an unequivocal visual communication signal. While the interpretation of the signal and the associated response of the receiver during visual communication are difficult to determine, the concept of the component assembly is similar to a typical language within which individual words often have multiple meanings, but when they appeared together with other words, the message becomes unequivocal. The present study thus demonstrates that dynamic body pattering, by expressing unique sets of key components acutely, is an efficient way of communicating behavioral information between oval squids.

Eleven Novel Polymorphic Microsatellite Loci for Oval Squid Sepioteuthis Lessoniana (Shiro-Ika Type)

The oval squid Sepioteuthis lessoniana is one of the most economically important squid species in Japan; however, its population structure is poorly understood due to the lack of hypervariable markers. Such information is critical for managing sustainable fisheries, as well as for ensuring the existence of wild S. lessoniana stocks. Eleven candidate microsatellite loci were isolated from a small insert genomic DNA library. Polymorphisms in these 11 loci were screened in 24 wild individuals. The number of alleles per locus was found to range from 5 to 19 alleles, and the observed heterozygosity ranged from 0.292 to 0.958. No evidence for linkage disequilibrium was detected among all the loci. The genotypic proportions conformed to Hardy-Weinberg equilibrium, except at one locus. In conclusion, these polymorphic microsatellite loci may be used to develop a genetic framework to manage S. lessoniana in the future.

Distribution of glutamic acid decarboxylase immunoreactivity within the brain of oval squid Sepioteuthis lessoniana

AB Aquatic Biology Contact the journal Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AB 19:97-109 (2013) - DOI: https://doi.org/10.3354/ab00525 FEATURE ARTICLEDistribution of glutamic acid decarboxylase immunoreactivity within the brain of oval squid Sepioteuthis lessoniana Shiori Kobayashi1, Chitoshi Takayama2, Yuzuru Ikeda1,* 1Department of Marine and Environmental Sciences, Graduate School of Engineering and Science, and 2Department of Molecular Anatomy, Graduate School of Medicine, University of the Ryukyus, Okinawa 903-0213, Japan *Corresponding author. Email: ikeda@sci.u-ryukyu.ac.jp ABSTRACT: Coleoid cephalopods (squid, cuttlefish, and octopus) have the largest and most complex brains of all invertebrates and show behavioral abilities similar to those of vertebrates. Among the coleoids, the oval squid Sepioteuthis lessoniana forms well-structured schools that are indicative of sociality. These behaviors are reflected in aspects of the well-developed brain. In this study, we focused on the role of the cephalopod brain in complex behavior. In order to reveal the network of γ-aminobutyric acid (GABA) in coleoids, we examined the immunohistochemical localization of glutamic acid decarboxylase (GAD), which is the synthetic enzyme of GABA, in the brain of young S. lessoniana. We found that GABAergic neurons and their axons were distributed throughout the brain. GABA neurons were abundantly localized in the inferior frontal lobe, which is involved in controlling arm motions, and in the subesophageal masses, which are lower and intermediate centers of action. GABAergic fibers were abundantly localized in the tract that runs from the superior frontal lobe to the vertical lobe. These results suggested the involvement of GABA in both cognitive behaviors (such as learning and memory) and in movement. KEY WORDS: Glutamic acid decarboxylase · Neurotransmitter · Brain · Oval squid · GABA · γ‑aminobutyric acid Full text in pdf format Information about this Feature Article NextCite this article as: Kobayashi S, Takayama C, Ikeda Y (2013) Distribution of glutamic acid decarboxylase immunoreactivity within the brain of oval squid Sepioteuthis lessoniana . Aquat Biol 19:97-109. https://doi.org/10.3354/ab00525 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AB Vol. 19, No. 2. Online publication date: September 24, 2013 Print ISSN: 1864-7782; Online ISSN: 1864-7790 Copyright © 2013 Inter-Research.

Ontogeny of the brain in oval squid Sepioteuthis lessoniana (Cephalopoda: Loliginidae) during the post-hatching phase

Among invertebrates, cephalopods have one of the most well-organized nervous systems. However, with respect to the ontogeny of the nervous system, the post-embryonic development of the cephalopod brain has only been documented for a few species. Here, we investigated the development of the brain of captive oval squid Sepioteuthis lessoniana during the post-hatching phase. The central part of the brain of the oval squid is divided into four main regions, namely, the supraoesophageal, anterior suboesophageal, middle suboesophageal, and posterior suboesophageal masses, each consisting of several lobes. At various ages in juvenile squid, the total volume of the central part of the brain (except the optic lobe) is significantly correlated with its body size, indicated by mantle length and wet body weight. The vertical lobe, superior frontal lobe, and anterior subesophageal mass drastically increase in relative volume as the squid grows. In contrast, the middle suboesophageal mass and posterior suboesophageal mass do not increase in volume with increasing squid age and body size. The effects of these results have been discussed in relation to the onset of squid behaviours during post-hatching.

Observations of schooling behaviour in the oval squid Sepioteuthis lessoniana in coastal waters of Okinawa Island

The schooling behaviour of the oval squid Sepioteuthis lessoniana was observed over 4 summers at 3 observation sites in the coastal waters of Okinawa Island, Ryukyu Archipelago, Japan. During this field study, 3 static appearances (belt, ball and sheet shape) and 2 transitional appearances (high and low density) were noted, recorded and described. In addition to formations, a member of S. lessoniana schools also displayed particular and repeated behavioural patterns such as vanguard and intimidating display. The 3 observation sites were tropical coral reefs near the coastline at a depth of 1 to 15 m on an average. All participating observers snorkelled and were equipped with various underwater digital video and photographic cameras. The schools observed consisted of 8 to over 100 members with a wide range of body sizes. Despite these biological and locational differences, both static and transitional appearances were consistently observed with equally consistent individual behavioural patterns. There have been studies on related species, Sepioteuthis sepioidea, at the San Blas Islands along the Caribbean coast of eastern Panama, and the same species, S. lessoniana, at a different geographical location, Casuarina Beach on Lizard Island, Australia. The findings of this study are consistent with those reported previously, with some notable differences.

Ontogeny of schooling behavior in the oval squid Sepioteuthis lessoniana

In contrast to schooling behavior in fish, which is well documented, the schooling behavior of an evolutionary counterpart, squid, has not been adequately described in the literature. In the current study, we investigated the ontogeny of schooling behavior in the oval squid Sepioteuthis lessoniana reared from hatching to about two months of age. During the two months of development, the distance and angle between nearest-neighbor individuals decreased from 5.3 mantle lengths (ML) to 1.8 ML and from 42.7° to 24.2°, respectively. In addition, the swimming distance of individuals in experimental duration decreased from 530.4 to 79.9 ML, and the relative swimming speed also decreased from 17.1 to 4.6 ML/s during the same period, with increasing synchronized hovering of individuals. These observations clearly suggest that oval squid swim randomly until 20 days after hatching, then form a school 30–60 days after hatching with an inter-individual distance of 2.0 ML. At two months after hatching, oval squid individuals swam in a parallel orientation and formed a belt-shaped arrangement, similar to the adult schooling behavior observed in natural populations.

Gradients of strain and strain rate in the hollow muscular organs of soft-bodied animals

The cylindrical shape of soft-bodied invertebrates is well suited to functions in skeletal support and locomotion, but may result in a previously unrecognized cost-large non-uniformities in muscle strain and strain rate among the circular muscle fibres of the body wall. We investigated such gradients of strain and strain rate in the mantle of eight long-finned squid Doryteuthis pealeii and two oval squid Sepioteuthis lessoniana. Transmural gradients of circumferential strain were present during all jets (n = 312); i.e. for a given change in the circumference of the outer surface of the mantle, the inner surface experienced a greater proportional change. The magnitude of the difference increased with the amplitude of the mantle movement, with circular muscle fibres at the inner surface of the mantle experiencing a total range of strains up to 1.45 times greater than fibres at the outer surface during vigorous jets. Differences in strain rate between the circular fibres near the inner versus the outer surface of the mantle were also present in all jets, with the greatest differences occurring during vigorous jetting. The transmural gradients of circumferential strain and strain rate we describe probably apply not only to squids and other coleoid cephalopods, but also to diverse soft-bodied invertebrates with hollow cylindrical or conical bodies and muscular organs.

Egg Case Containing Three Ova of Oval Squid Sepioteuthis lessoniana in Okinawa Island of the Ryukyu Archipelago

Egg Case Containing Three Ova of Oval Squid Sepioteuthis lessoniana in Okinawa Island of the Ryukyu Archipelago

Reproduction and life span of the oval squid Sepioteuthis lessoniana (Cephalopoda: Loliginidae): comparison between laboratory-cultured and wild-caught squid

Three consecutive generations of the oval squid, Sepioteuthis lessoniana , were cultured between October 2000 and May 2002 to investigate the life history of this species. Starting with the parental generation (wild-caught sub-adult squid from Tokushima Prefecture, Japan), we successfully obtained first and second generations. Life span and maturation of cultured oval squid and wild oval squid caught from the same habitat during April 2001 through to March 2002 were compared. Captive squid matured earlier and had a shorter life span (189–247 days) than the wild-caught squid (approximately one year) but reached an equivalent final body size. More ova were found in the oviducts of cultured females than in the oviducts of wild-caught females. Ultimately, collapse of the culture population was mainly due to the low rate of embryonic development of spawned ova, which might have resulted from the abnormal arrangement of ova in egg cases produced by later generations of females.

Taste-active components in the mantle muscle of the oval squid Sepioteuthis lessoniana and their effects on squid taste

Using a series of omission and addition tests and sensory evaluation of synthetic extracts, the taste-active components of the mantle muscle of the oval squid (Sepioteuthis lessoniana) were determined to be glycine, alanine, proline, glutamate, arginine, adenosine 5'-monophosphate, trimethylamine oxide, glycine betaine, as well as potassium, sodium, and chloride ions. A simplified synthetic extract prepared from these 11 taste-active components was found to almost reproduce the taste of the complete synthetic extract containing 45 components of S. lessoniana muscle. This was also the case for three other squid species; Loligo bleekeri, Loligo edulis, and Todarodes pacificus. When certain components were added to the simplified synthetic extracts of these three squid species - sodium ions and glycine for L. edulis, sodium ions and arginine for L. bleekeri, chloride ions, glycine, and arginine for T. pacificus - the taste of the simplified synthetic extracts approximated the extract from S. lessoniana, which had the most preferred taste.

Mirror image reactions in the oval squid Sepioteuthis lessoniana

Mirror image reactions in the oval squid Sepioteuthis lessoniana

Ontogeny of mantle musculature and implications for jet locomotion in oval squid Sepioteuthis lessoniana

Ontogeny of mantle musculature and implications for jet locomotion in oval squid Sepioteuthis lessoniana

Alternative Male Mating Behaviors Dependent on Relative Body Size in Captive Oval Squid Sepioteuthis lessoniana (Cephalopoda, Loliginidae)

We observed the reproductive behavior of the oval squid Sepioteuthis lessoniana in captivity. The male used three different mating behaviors: male-parallel (MP), male-upturned (MU) and sneaking. Male competition over females frequently occurred before and during the female egg-laying period, and the outcome of most fights depended on male body size. Larger males guarded their partners from other males and performed MP mating during the egg-laying period of the paired females. In contrast, there was no pairing and mate guarding in MU mating and sneaking, which were adopted by smaller subordinate males as alternative tactics outside female egg-laying period and during the period, respectively. MP matings were 95% successful, but more than half of MU matings were unsuccessful. Higher mating success in MP mating was achieved through pairing, whereas males in MU mating were less successful because mating attempts without pair formation were often foiled by escape of the female. Sneaking was successful in all cases but occurred less frequently. Spermatophores were attached at the opening of the oviduct in MP mating, whereas they were attached around the female buccal membrane in MU mating and sneaking. Considering the route of egg transportation, higher fertilization success can be expected in MP mating because of the advantageous location of the attached spermatophores. Our results suggest that MP mating is used by larger, paired males during the female egg-laying period, and that MU mating and sneaking are alternative tactics adopted by smaller, subordinate males. These alternative mating behaviors would be conditional strategy dependent on relative body size, because some individual males displayed both MP and MU mating behaviors.

Size selectivity of a trammel net for oval squid Sepioteuthis lessoniana

The size selectivity of a trammel net for herded oval squid Sepioteuthis lessoniana in Tateyama Bay, Chiba Prefecture, was estimated by comparison between the mantle length frequency distributions of oval squid caught by a trammel net and by a set net. The measured mesh sizes of the inner net of the trammel net and of the final section of the set net were 85.3 and 11.3 mm, respectively. In the trammel net fishery where oval squid are herded into the net, most of the oval squid are caught in the bag-shaped inner net. Hence, the logistic function was employed for the size selectivity curve of the trammel net. The ‘share each length's catch total’ (SELECT) model was implemented for the estimation of the selectivity curve. The size selectivity r(l) of the trammel net for the oval squid was expressed as a logistic function of the mantle length l: r(l)=exp (-18.57+0.88 l)/[1+exp (-18.57+0.88 l)]. From these logistic parameter estimates, the 50% selection mantle length and selection range (L75-L25) were calculated as 21.07 and 2.49 cm, respectively. The selection probability of oval squid whose mantle girth was equivalent to the mesh perimeter of the inner net was 0.09. Accordingly, oval squid of a girth smaller than the mesh perimeter were likely to pass through the mesh to escape from the net.

Transport of the oval squid Sepioteuthis lessoniana Ferussac, 1831 in Lesson 1830-1831 (Cephalopoda: Loliginidae) for up to 24 h and subsequent transfer to an aquarium

: Conditions for transporting live young and subadults of the squid Sepioteuthis lessoniana were investigated in a laboratory experiment and transport trial. In the lab experiment, survival was examined for various seawater conditions and transport procedures. The quality of the water containing the squid decreased (pH 4°C) after 24 h, but 12 of 33 examined squid (body weight (BW) 5.0–877 g) survived these changes. Squid survival was high when the BW : seawater volume ratio started below 30. Also, survival was higher in large containers such as a styrofoam box with large (>1620 cm2) bottom area. Based on these criteria, 24 squid (BW 2 h) acclimation period survived the transfer.