シリヤケイカの繁殖行動

The reproductive behavior of the Japanese spineless cuttlefish Sepiella japonica was observed in a tank. The males competed for females before egg-laying and then formed pairs with females. The male then initiated mating by pouncing on the female head, and maintained the male superior head-to-head position during the mating. Before ejaculation, the male moved his right (non-hectocotylized) arm IV under the ventral portion of the female buccal membrane, resulting in the dropping of parts of spermatangia placed there during previous matings. After the sperm removal behavior, the male held spermatophores ejected through his funnel with the base of hectocotylized left arm IV and transferred them to the female buccal area. The spermatophore transfer occurred only once during each mating. The female laid an egg capsule at average intervals of 1.5 min and produced from 36 to more than 408 egg capsules in succession during a single egg-laying bout. Our results also suggested one female produced nearly 200 fertilized eggs without additional mating, implying that the female have potential capacity to store and use active sperm properly. The male continued to guard the spawning female after mating (range=41.8-430.1 min), and repeated matings occurred at an average interval of 70.8 min during the mate guarding. Although the time spent on the sperm removal in S. japonica was shorter than in other sperm-removing cuttlefishes, the shorter sperm removal duration may be compensated by the post-copulatory mate guarding and repeated matings in this species.水槽内でのシリヤケイカSepiella japonicaの繁殖行動を観察した。シリヤケイカの雄は雌が産卵を開始する前に雌をめぐって闘争し,ペアを形成した。ペア雄は雌の頭部に覆い被さる形で交接を始め,雄上位のままで雌雄の頭部が向き合う交接体勢を維持した。雄は自らの精莢を射出する前に,雌の口球周口腹下部で右第IV腕を動かすことによって,過去の交接によってそこに付着させられていた精子塊の一部を落下させた。その精子除去行動後,雄は交接腕である左第IV腕の根元で漏斗から吐き出した精莢をつかみ,雌の口球下部に渡した。この精莢輸送は各交接で1回だけであった。雌は平均1.5分の間隔で産卵基質に卵嚢を1つずつ産みつけ,一連の産卵行動で36から408個以上の卵嚢を産出した。また,本研究では1個体の雌が追加の交接なして200個近くの受精卵を産出することが示され,シリヤケイカの雌は過去の交接によって貯えられた精子を必要な時に受精に使う能力を持つと考えられた。それに対して雄は交接後も産卵雌を他雄からガードし続け(交接後ガード時間の範囲=41.8〜430.1分),そのガード行動中に平均70.8分の間隔で繰り返し交接を行った。シリヤケイカの雄が精子除去に費やす時間は他のコウイカ類のそれらと比べて短かったが,永続的な交接後ガード行動と繰り返し交接が短時間の精子除去から推測された本種の低い精子置換率を補償しているかもしれない

Sperm removal, ejaculation and their behavioural interaction in male cuttlefish in response to female mating history

The removal of previously stored rival sperm and increased ejaculate expenditure are effective male sperm competition tactics to ensure paternity. We examined both behaviours and their interaction for male cuttlefish, Sepia lycidas, as a strategic investment. Males increased the duration of sperm removal and the number of ejaculations per mating when they were not the last male who had mated with the current partner. These responses would decrease the number of rival sperm and increase the male\u27s own sperm in the fertilization area. Recognition of the female\u27s mating history appeared to result from close mate guarding during successive matings. Moreover, when the last mate of the current partner was different from the current mate, there was a significant negative relationship between sperm removal duration and the number of subsequent ejaculations. This interaction suggests both strategic investment allocation and constraints on each mating investment as possible results of mating interruption by other males and spermatophore depletion, respectively. In addition, larger males with high competitive ability prolonged sperm removal when the last mate of the current partner was different from the current mate, whereas smaller males with relatively larger testes ejaculated more times during a mating. Male S. lycidas might adjust the duration of sperm removal at the risk of failing to achieve ejaculation and allocate their finite ejaculate expenditures based on the results (i.e. the increasing proportion of their own sperm)

Sperm displacement behavior of the cuttlefish Sepia esculenta (Cephalopoda: Sepiidae)

Sperm displacement behavior of cuttlefish (Sepia esculenta) was observed in a tank. Before ejaculation, male cuttlefish used their arms III to scrape out sperm masses attached to the buccal membranes of females. The removed sperm mass debris was directly visible and countable. Active sperm were present within the removed sperm debris, implying that the aim of this behavior is to remove competing male sperm. However, many sperm masses remained on the female buccal membrane even after the removal behavior, showing that sperm removal in S. esculenta is incomplete. The duration of sperm removal (an indicator of male investment in that process) was unaffected by the body sizes of mated pair, the duration of spermatangia placement at the current mating (for the hypothesis that the sperm removal serves to creat attachment space of spermatophores), or the estimated amount of sperm masses deposited from previous matings. Moreover, male S. esculenta performed sperm removal regardless of whether the last male to mate with the partner was himself, suggesting males remove not only the sperm of rivals but also their own. Although the number of removed sperm masses increased with the time spent on removal of sperm, male cuttlefish may shorten the duration of sperm removal to avoid the risk of mating interruption. We conclude that this time restriction would likely influence the degree of partial sperm removal in S. esculenta. A digital video image relating to the article is available at http://www.momo-p.com/showdetail-e.php?movieid=momo040729se01a

Neritic squid resources and cuttlefish resources in Japan

Knowledge concerning biology of two loliginids and three sepiids which are found in the Japanese waters was reviewed including unpublished information of the authors. The swordtip squid, Photololigo edulis, is one of the most important resources for the coastal fisheries of Kyushu and the prefectures facing the southwest Japan Sea. This species is the only species of genus Photololigo found along the Japanese mainland coast and is easily distinguished from other loliginids, by the light organs on the ink sac. The species is distributed from southern Japan to the Red Sea. The spawning season extends throughout the year. Egg cases are laid in clusters on the sandy bottom. The life span is about one year. In the juvenile stage they feed on Crustacea and after reaching pre‐maturity they prey mainly on fish, but many have empty stomachs. Most catches are made by jigging and trawler. The fishing season extends throughout the year. The fishing grounds are widely spread over the continental shelf. Annual catches are around 25 000 metric tonnes. Although this level varies from year to year, it is fairly stable. Fishing has probably little effect on the stocks. The spear squid, Heterololigo bleekeri, can be easily distinguished from other loliginids by its shorter tentacles. The species is endemic in the Far East waters. The stocks are larger in the north. The spawning season is winter in south Japan, and from spring to early summer in north Japan. Egg cases are laid beneath the undersurfaces of firm substances. The life span is about one year. Its feeding behaviour is similar to that of the swordtip squid. Catches are made mainly with bottom trawler and fixed nets from autumn to spring. Annual landings fluctuate widely from year to year. Several prefectures along the northern Japan Sea coast are promoting the large scale development of artificial spawning beds of the species to increase the stocks. The three sepiids, golden cuttlefish. Sepia esculenta, kisslip cuttlefish. Sepia lycidas, and spineless cuttlefish, Sepiella japonica are important in mainland Japan. Those three spawn from spring to early summer in the innermost waters of semi‐enclosed inlets. Eggs are laid in batches of 50–300 every day for 3–4 days followed by a rest period of 1–2 days. This pattern is repeated until several thousands of eggs have been laid. The life span of Sepia esculenta and Sepiella japonica is one year. They feed mainly on decapod crustaceans and fish but as growth proceeds the proportion of fish increases. They are fished mainly by cuttlefish trap and beam trawler. In the early 1960s annual landings were 20 000 metric tonnes but since 1980 catches have decreased below 10 000 metric tonnes. Of the three species, the stock of Sepiella japonica is the most fluctuable. Judging from the result of the stock assessment studies on Sepiella japonica in the western Inland Sea, their stocks have been over‐exploited

Age and growth estimation of the European squid, Loligo vulgaris, based on statolith microstructure

Age and growth were estimated in the European squid, Loligo vulgaris, by examining growth increments in the statoliths of 203 specimens collected from off the French Mediterranean coast. Length and increment data were analyzed assuming that the increments were formed daily. The relationships between age and length showed that: growth rate varied considerably among individuals; growth was double exponential; the squids grew on average to 240 mm ML at 240 d from hatching, with a maximum of 350 mm at 240 d; the life span is probably about one year

Karyological studies on seven cephalopods

Karyological studies were made on the embryos of seven cephalopods using chopping method. Two sepiids (Sepia esculenta and Sepia lycidas) and three loliginids (Sepioteuthis lessoniana, Heterololigo bleekeri and Photololigo edulits) were all 2n = 92). Their karyotypes and total length of chromosomes were slightly different from each other. Two octopuses (Octopus ocellatus and O. vulgaris) were both 2n=60. Their karyotypes and total length of chromosomes were, however, remarkably different from each other

Range extension of three crangonid shrimps (Decapoda, Caridea) to Japanese waters

A range extension to Japanese waters is recorded for three crangonid shrimps: Lissosabinea indica (De Man, 1918) previously only known from the Philippines and Indonesia; Parapontocaris levigata Chace, 1984 known from the Indo-West Pacific up to Taiwan; and Rhynocrangon sharpi (Ortmann, 1895) known from the northern North Pacific including the Far East Russian coast of the Sea of Japan. The first two species are the only members of their genera recorded from Japan. Diagnosis and illustrations are given for L. indica and P. levigata for the species recognition. Rhynocrangon sharpi is fully redescribed and illustrated, because there is no detail description of this species

Age and growth of loliginid squid Photololigo edulis (Hoyle, 1885)

Age and growth were estimated on two brood stocks of a loliginid squid, Photololigo edulis (Hoyle), by examining growth increments within the statoliths from 773 specimens. Samples were collected from the northwestern coast of Kyushu, Japan, and the southwestern coast of the Sea of Japan between January 1983 and June 1984. Length and age data were fitted to logistic growth curves for each sex and brood, under the assumption that increments formed daily. Relationships between age and mantle length and the modelled growth curves showed that: the posthatch life span may be < 1 yr; growth rates vary considerably between individuals, especially in the second half of life; the average growth rate of the male was higher than that of the female in the warm-season brood, but almost the same in the cold-season brood. Because of the wide variation in the individual growth rate, it was presumed that warm- and cold-season broods were not genetically discrete populations