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)

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

Age, growth, and mortality of Loligo vulgaris wild paralarvae : implications for understanding of the life cycle and longevity

Peer reviewedPreprin

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

Gonadal sex differentiation and development during early ontogenesis in the breeding kisslip cuttlefish (Sepia lycidas)

To understand and obtain basic information on sex differentiation in the kisslip cuttlefish (Sepia lycidas), the gonadal sex differentiation process was investigated histologically. An undifferentiated gonad consisting of germ cells and somatic cells was found to form at a caudal site in the space between the internal yolk sacks of cuttlefish embryos at 14 and 21 days after spawning (DAS). Sexual dimorphism in the gonad was first detected at around 28 DAS. Meiotic oocytes were observed as the first visible morphological characteristic of ovaries in the gonads of some cuttlefish embryos at 28 DAS. In other individuals, neither meiotic germ cells,nor the appearance of a testicular structure, were observed in the gonad even after 10 days post hatching (DPH). Seminiferous tubules, consisting of a small number of spermatogonia and a surrounding basement membrane,were the first visible morphological characteristic of the testis in the male gonad, detected at around 20 DPH. This is the third report on the gonadal sex differentiation process in cephalopods