Monogamous Mating System and Spawning Cycle in the Gobiid Fish, Amblygobius phalaena (Gobiidae)

Reproductive ecology and mating system of the gobiid fish, Amblygobius phalaena, were studied on the coral reef at Sesoko Island, Okinawa, Japan. This goby usually lives in pairs, and maintains territories with several burrows for shelter and spawning. Although a few paired individuals changed partners, most pairs remained together over successive rounds of reproduction. Mate guarding by females appeared to prevent males from mating with other females. Spawnings were synchronous with semilunar periods. Several expected spawnings failed to occur (12%). These may have been caused by the delays in spawning preparation of the paired females or by the disturbance caused by a typhoon. A pair spawned in one of the several burrows within their home ranges. Eggs were deposited on the ceiling of the burrow, and were tended by the paired male for 3–4 days until embryos hatched. The males tended eggs at the expense of their feeding. Aggression toward fishes approaching their burrows were exhibited by the males as well as the females. Because of its low frequency in females, this behavior did not limit their ability to feed

Responses of the egg-tending gobiid fish Valenciennea longipinnis to the fluctuation of dissolved oxygen in the burrow

Responses of the egg-tending male Valenciennea longipinnis (Gobiidae), a species inhabiting the near-shore moat on coral reefs, to the fluctuation of dissolved oxygen (D.O.) concentration in its enclosed burrow, were studied. D.O. concentration in egg-tending burrows decreased from high tide to low tide during the daytime. D.O. concentrations in 12 egg-tending burrows at low tide ranged from 2.17-4.50 ml D.O. L−1 (43.8-91.9% D.O. saturation) on the day after spawning. In the laboratory, an egg-tending male increased the frequency and duration of fanning as D.O. concentration decreased. Below about 1.2 ml D.O. L-1 (about 25% D.O. saturation), the frequency of fanning began to decrease. The frequency and duration of fanning increased with developmental stage of the eggs, perhaps in response to an increase in oxygen consumption of eggs with developmental stage. The rapid adjustments of fanning behavior to D.O. concentration in the burrow and developmental stage of the eggs showed indirectly that the primary role of fanning is a supply of oxygenated sea water to the eggs

Responses of the egg-tending gobiid fish Valenciennea longipinnis to the fluctuation of dissolved oxygen in the burrow

Responses of the egg-tending male Valenciennea longipinnis (Gobiidae), a species inhabiting the near-shore moat on coral reefs, to the fluctuation of dissolved oxygen (D.O.) concentration in its enclosed burrow, were studied. D.O. concentration in egg-tending burrows decreased from high tide to low tide during the daytime. D.O. concentrations in 12 egg-tending burrows at low tide ranged from 2.17-4.50 ml D.O. L−1 (43.8-91.9% D.O. saturation) on the day after spawning. In the laboratory, an egg-tending male increased the frequency and duration of fanning as D.O. concentration decreased. Below about 1.2 ml D.O. L-1 (about 25% D.O. saturation), the frequency of fanning began to decrease. The frequency and duration of fanning increased with developmental stage of the eggs, perhaps in response to an increase in oxygen consumption of eggs with developmental stage. The rapid adjustments of fanning behavior to D.O. concentration in the burrow and developmental stage of the eggs showed indirectly that the primary role of fanning is a supply of oxygenated sea water to the eggs

A New Feedback Method for Dy-namic Control of Manipulators

Asymptotic tracking and disturbance rejection in uncertain nonlinear systems is studied in the context of output feedback control. This study is facilitated by formalizing the notion ofk-fold exosystem and generalizing the internal model principle to the nonlinear setting

The influence of recovery period between exercise sessions on the muscle-hypertrophic effect of resistance training

学位の種別: 課程博士審査委員会委員 : （主査）東京大学教授 石井 直方, 東京大学教授 八田 秀雄, 東京大学教授 福井 尚志, 東京大学准教授 柳原 大, 東京大学准教授 寺田 新University of Tokyo(東京大学

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)

Testis size variation within sneaker males of the dusky frillgoby Bathygobius fuscus (Gobiidae): effects of within-tactic competition

A ‘sneaking tactic’ is an alternative reproductive strategy that usually results in sperm competition among males with different tactics. Relatively large testes are a sneaker-specific trait that has generally been thought to have evolved due to sperm competition between sneaker males and bourgeois (guarding) males. However, here we show that competition among sneaker males can also affect testis enlargement in the dusky frillgoby (Bathygobius fuscus) sneaker males. The competitive advantage of focal sneaker males was experimentally manipulated by placing them in tanks with either relatively smaller or larger males. Testis enlargement was conspicuous in focal males that were cohoused with larger males. Smaller sneaker males may invest more in testicular growth because they are at a competitive disadvantage in physical contests for sneaking opportunities among sneaker males and consequently may be confined to making relatively late intrusions during spawning into nests that have a higher risk of sperm competition. Another possible reason for the relative size-dependent energy investment in testes may be increased investment by large sneaker males in aggressive interactions for sneaking opportunities. This is the first evidence that testis size variation among sneaker males is affected by the competition among sneaker males