Mating games squid play: reproductive behaviour and sexual skin displays in Caribbean reef squid Sepioteuthis sepioidea

Observation of the sexual interactions of Sepioteuthis sepioidea squid during the short reproductive stage of their lives showed a scramble competition system, with both male and female polygyny. Mature females were faithful to a specific location in the daytime, whereas males moved from group to group and formed short-term consortships with females. Males defended females from other males, particularly with an agonistic Zebra display. Male–female pairs exchanged Saddle-Stripe displays, after which males might display an on–off Flicker. There was considerable female choice. Only if a female responded to this display with a parallel Rocking action would she pair and would the male deposit spermatophores at the base of her arms, and only 50% of the time did females move the spermatophores internally to where sperm might be released and stored in the oviducal gland for later fertilization of eggs. This long-term set of interactions and solitary deposition of hidden egg strings contrasts with the attraction of both sexes to a common ‘egg mop’ laid by many females which was a site of competition in other loliginid squid. Since Sepioteuthis is a primitive genus within the family Loliginidae, it may represent a generalist reproductive strategy that evolved into a specialized localization one.     

Preparation and physico-chemical characterization of chitin and chitosan from the pens of the squid species, Loligo lessoniana and Loligo formosana

β-chitin and its chitosan from the pens of Loligo lessoniana and Loligo formosana has been isolated, prepared, and physico-chemically characterized to demonstrate a potential chitin source. Without deminerization due to negligible ash content, only deproteinization was used in the chitin isolation with an yield of 35–38%, without significant difference either between the two species or the collection seasons. Reducing step not only saves production cost but also obviates acid pollutant. Mild alkaline deacetylation with various time periods was employed in the chitosan preparation. Optical rotation and thermal transition of chitin from both species suggested the weak intermolecular forces compared with shrimp chitin. The results of nitrogen contents indicate the effectiveness of the deproteinization method used. The samples were categorized as a Class III: moderate hygroscopicity. Traces of elements presented in pens markedly decreases but are incapable to be got rid of within the step of chitin–chitosan preparation. In addition, a small amount of cadmium, as the contamination, was detected in the samples from L. formosana.     

The Hemocyanin of the Squid Sepioteuthis lessoniana: Structural Comparison with Other Cephalopod Hemocyanins

The subunit structure of the hemocyanin from the squid Sepioteuthis lessoniana has been characterized by analytical sedimentation. The protein exists free in the hemolymph as a 60S, multisubunit structure with a molecular mass of approximately 4.0 × 10⁶ gm/mol. At extremes of pH this can be dissociated into 10 monomers, of mass 3.8 × 10⁵ gm/mol each.At neutral pH, if 5 mM Mg²⁺ or less is present, the monomers associate to form a dimer of molecular mass 7.7 × 10⁵ gm/mol. In the pH range from 10.5 to 7.5, formation of the dimer is facilitated by the binding of one proton per monomer. If the magnesium concentration is raised to 25 mM or more, the dimers reversibly and completely associate into decamers. This process is shown to require the binding of 10 magnesium ions.In its size, subunit structure, and behavior with respect to association–dissociation processes, Sepioteuthis hemocyanin resembles the corresponding proteins of other squid much more than it does those of Octopus or Nautilus.     

Physiological color change in squid iridophores

Summary Cephalopods generally are thought to have only static iridophores, but this report provides qualitative and quantitative evidence for active control of certain iridescent cells in the dermis of the squidLolliguncula brevis. In vivo observations indicate the expression of iridescence to be linked to agonistic or reproductive behavior. The neuromodulator acetylcholine (ACh) induced dramatic optical changes in active iridophores in vitro, whereas ACh had little effect on passive iridophores elsewhere in the mantle skin. Bath application of physiological concentrations of ACh (10^-7M to 10^-6M) to excised dermal skin layers transformed the active iridophores from a non-reflective diffuse blue to brightly iridescent colors, and this reaction was reversible and repeatable. The speed of change to iridescent in vitro corresponded well to the speed of changes in the living animal. Pharmacological results indicate the presence of muscarinic receptors in this system and that Ca⁺⁺ is a mediator for the observed changes. Although ACh is present in physiological quantities in the dermal iridophore layer, it is possible that ACh release is not controlled directly by the nervous system because electrophysiological stimulation of major nerves in the periphery resulted in no iridescence inL. brevis; nor did silver staining or transmission electron microscopy reveal neuronal elements in the iridophore layer. Thus, active iridophores may be controlled by ACh acting as a hormone.     

Vigilance and antipredator responses of Caribbean reef squid

Antipredator responses, especially those of open-ocean squid, have been seldom studied in the natural environment. Sepioteuthis sepioidea, observed by snorkellers near the shore in early morning/late afternoon, produced an average of eight moves of over 1?m per hour, apparently mostly antipredator behaviours. Close approaches by herbivorous parrotfish elicited no response in 74% of encounters; otherwise, squid produced agonistic zebra stripes or startle-mantle-dots skin patterns. Predatory bar jack fish caused flight but not zebra displays, and squid usually paled and fled quickly (66%) from snapper. The speed of approach was the best predictor for flight and display responses to snapper, but for bar jack and parrotfish, the relative fish size and distance were the predictors for escalated responses. Paired dorsolateral mantle dots were produced when squid approached the sea bottom or hunted outside the group and in reaction to fish approaches; 56% of these were to the very common parrotfish. Reactive pairs of spots were selected from four possible mantle locations and they were significantly likely to be directional towards fish, presumably as startle/warning, but not directed towards conspecifics as indicators of predator presence. Thus the evasion techniques of the cephalopods and their ability to produce different display patterns on the skin show how an intelligent animal modifies an otherwise simple decision about which pairs of spots to select from four possible mantle locations and whether to flee from potentially dangerous animals.     

莱氏拟乌贼缠卵腺的显微与超微结构

为了解莱氏拟乌贼(Sepioteuthis lessoniana)缠卵腺的结构和功能,本研究采用组织切片技术和透射电镜技术对该腺体进行显微与超微结构观察.结果显示,缠卵腺由腺壁组织、分泌叶瓣和结缔组织组成.其中,腺壁组织由外膜层和肌肉层组成,位于腺体外部;分泌叶瓣是腺体的主要部分,由分泌细胞和支持细胞组成,分泌细胞具有...