海産ツボワムシ類の浮遊性休眠卵の出現

Resting eggs of the rotifers Brachionus plicatilis and B. rotundiformis are generally found in the bottom sediments in the nature. Here, environmental conditions tend to inhibit the hatching of resting eggs because oxygen concentrations and light levels are low. However, several workers have also reported the appearance of floating resting eggs in these species. These are characterized by a black ring inside of the extra-embryonic space. If this floating behavior can be utilized to avoid the inhibitory environmental effects which reduce the hatching rate of these eggs, then this mechanism clearly has important ecological significance. In this study, the factors which induce flotation in resting eggs were investigated in the laboratory. Changes in temperature, salinity, photoperiod, dissolved oxygen and ammonium sulfate concentration did not increase the frequency of floating eggs in either species, irrespective of the developmental stage of the egg. Floating eggs appeared only when resting eggs were exposed to air. These results suggested that flotation of resting eggs may not be due to a biological process in the normal life cycle of the rotifer. It seems more likely that it occurs as an artifact derived from the methods used in handling mud samples or managing of rotifer cultures.海産ツボワムシの休眠卵はふつう沈降性を示し,天然では汽水域の底泥中に分布するが,孵化直前の休眠卵の中には,卵空室部にガスがたまって浮遊性を示す例が報告されている。休眠卵の孵化には光照射が必要なので,前述の現象を孵化に阻害的な底質環境を回避する手段と捉えることができるかもしれない。その形成機構を2種の海産ツボワムシ(Brachionus Plicatilis, B. rotundiformis)の休眠卵を材料として調べた。環境因子(水温,塩分,光条件,溶存酸素量,硫化アンモニウム濃度)を様々に調節して,卵の保存とインキュベートを行ったが,浮遊卵の出現は全く観察されなかった。一方,乾燥処理や培養槽の瀑気など,休眠卵と空気の接触の影響をみたところ,卵空室部内にガスが取り込まれ,浮遊卵が高率で出現した。この現象は2種のワムシに共通にみられた。したがって,この現象を,孵化に必要な光照射の機会を増大するための手段として考えることは難しい。過去の浮遊卵の観察例は,休眠卵を分離する際に採取した底泥を乾燥したり,培養槽に通気を施すなどの人工的な操作に基づくものと考える。既往の知見と併せると,底泥に分布する休眠卵は光の直接照射よりも光化学的な作用機構によって孵化する可能性が高い

Charge-discharge Performance of an Ionic Liquid-based Sodium Secondary Battery in a Wide Temperature Range

A sodium secondary battery has been constructed by using a nonvolatile and nonflammable Na[FSA]-[C(3)C(1)pyrr][FSA] (FSA = bis(fluorosulfonyl)amide, C(3)C(1)pyrr = N-methyl-N-propylpyrrolidinium) ionic liquid, a NaCrO(2) positive electrode and a Na metal negative electrode. The charge-discharge performance is evaluated over a wide temperature range of −20–90℃. It has been demonstrated that the sodium secondary battery has long cycle lives both at a high temperature of 90℃ and at a low temperature of 0℃. Thus, the ionic liquid-based sodium secondary battery is expected to be a viable alternative to lithium ion battery for many applications

Mate Recognition of the Rotifer Brachionus plicatilis Muller at Different Temperatures

Recent studies on sexual isolation among euryhaline Brachionus species suggest that differences in the molecular structure of a mate recognition pheromone (MRP) are important in maintaining reproductive isolation. It has not been clarified whether environmental conditions can affect MRP structure and the responsiveness. The objective of this study was to examine the effect of temperature on mate recognition of the rotifer B. plicatilis. Three strains (Russian, German, and Tokyo) of B. plicatilis were cultured on Nannochloropsis oculata and a series of intra- and interstrain matings were made using female and male rotifers reared at three temperatures, 15, 20 and 25℃. Matings were conducted for nine combinations of treatments (3 strains x 3 temperatures). Temperature affected the attempted matings (frequency of circling behavior per male/female contact) differently among strains and sexes. Culture temperature of females affected the frequency of mating attempts. Male recognition of females occurred best at 20℃ for Russian strain. German strain males only recognized females when females were reared at less than 20℃. For Tokyo strain, however, rearing temperature of females did not affect mate recognition. MRP antibody binding did not correlate with the frequency of male mating attempts at each temperature

カイアシ類, ミジンコ類及びワムシ類に対する内分泌かく乱化学物質の急性毒性濃度

Reports have been increasing on the deleterious effect of endocrine disrupting compounds (EDCs) on marine inhabitants. Zooplankton, the primary consumer in the aquatic ecosystem are not spared on these effect. As a first step to investigate the chronic and reproductive effects of EDCs on marine zooplankton, we determined the acute toxic concentration of the known and suspected EDCs for vertebrates including two natural hormone (testosterone, 17β-estradiol), three estrogenic compounds (nonylphenol, octylphenol, bisphenol A), six pesticides (isoprothiolane, methoprene, fenitrothion, diazinon, iprofenfos, pyroquilon) and a herbicide (mefenacet) on the copepod Tigriopas japonicus, the cladoceran Diaphanosoma celebensis and the rotifer Brachionus plicatilis. Compound exposure was carried out in 6-well polysterene plates, and mortality was evaluated after 24 h. Although the three zooplankton depicted different sensitivities toward different compounds, a dose-response relationship was consistent in all cases. B. plicatilis was particularly resistant to most of the compounds tested, while T. japonicl.ls and D. celebensis are comparatively sensitive. The data presented herein can be a basis for the determination of concentrations to be used in chronic and endocrine disruption experi-ments using marine zooplankto

Electrochemical Capacitors Using Fluorohydrogenate Ionic Liquid Electrolytes

Electrochemical capacitors using fluorohydrogenate ionic liquids show a large voltage dependence of capacitance with a maximum at a charging voltage around 2.5 V, resulting in a larger capacitance than those using other typical ionic liquid electrolytes. The voltage dependence becomes less remarkable with decrease in the HF composition n in EMIm(FH)nF (EMIm: 1-ethyl-3-methylimidazolium). Cyclic voltammetry using an activated carbon working electrode revealed that two redox reactions occur at the higher and lower potentials against the rest potential in EMIm(FH)2.3F. These Faradaic processes contribute to the voltage dependence of capacitance

Behavior and reproduction of the rotifer Brachionus plicatilis species complex under different light wavelengths and intensities

We investigated the influence of light on phototactic behavior and reproduction in two species of rotifer from the Brachionus plicatilis species complex (B. plicatilis sensu stricto (s. s.) and Brachionus manjavacas). This was done to understand how light effects these species so that we might use this knowledge to establish a more efficient aquaculture protocol. We used four different light wavelengths (white, with peaks at 460 and 570?nm; blue at 470?nm; green at 525?nm; and red at 660?nm) and four intensities (i.e., 0.5?30.0?W/m2). Using micro-spectrophotometry we determined that eyespots of these two Brachionus species absorbed blue and green light 5.5 times more than red light. B. plicatilis s. s. showed positive phototaxis under white, blue, and green light at lower light intensities, but no phototaxis under red light at all intensities (0.5, 6.2, 15.0, and 30.0?W/m2). Similar patterns of phototaxis were observed in B. manjavacas and did not differ among mictic, amictic females, and male rotifers. Population growth rate of B. plicatilis s. s. under dark condition was 1.1?1.2 times higher than that under white light condition. No significant differences were observed in population growth rate at 3.8 and 6.2?W/m2 at all light wavelengths. On the other hand, population growth rates at 0.5 and 1.6?W/m2 were the lowest under blue light. According to these results, both wavelength and intensity of light affect the population growth of rotifers, which in turn may be influenced by the rotifers\u27 wavelength-dependent phototaxis

ワムシの生殖に与える光波長の影響

The monogonont rotifer Brachionus manjavacas (Australian strain) showed a steadily increasing population growth and larger number of resting egg production under continuous white light compared to under total darkness when they were batch cultured. By comparing different wavelength of light, such as white (control), 470 (blue), 525 (green) and 660 (red) nm, rotifers showed no significant differences in specific population growth rate, but sexual reproduction showed different patterns associated with light wavelengths. Although there were no significant differences with regard to mixis induction, the resting egg formation actively occurred at 525 nm. We further observed the movement of female rotifers to find the influential factor of different sexual reproduction. There was no significant difference in the mean swimming speed of 10 female rotifers, but the proportion of settling individuals varied with light wavelength. Under 525 nm light, no individuals continuously settled for one minute, while under other light wavelengths the percent of settling females for a minute ranged between 6.1±5.4 and 23.8±6.5%. The higher ratio of swimming females at 525 nm should enhance the male/female encounters, which resulted in higher resting egg formation.シオミズツボワムシ複合種 Brachionus manjavacas （いわゆる L 型オーストラリア株、以下ワムシと略）を Tetraselmis 給餌によってバッチ培養したところ、暗黒下での培養よりも白色光の連続照射下で活発な個体群増殖と耐久卵形成を示した。次に、青 (470 nm)、緑 (525 nm)、赤 (660 nm)および白色光 (対照) の連続光照射下（約 1.4 W/m2）で培養し、個体群増殖率（r）、両性生殖誘導率、受精率、耐久卵数を求めた。異なる波長光の照射によってワムシの個体群増殖率と両性生殖誘導率に変化はなかったが、耐久卵形成は光波長 525 nm のとき最も活発に起こった。雌ワムシの遊泳速度は照射光波長にかかわらず一定だったが、付着行動を示す雌ワムシは光波長 660 nm のとき最も多くなった。一方、光波長 525 nm では付着個体が出現せず、全個体が遊泳した。光波長 525 nm のとき、雌ワムシの活発な遊泳行動によって、雄ワムシとの接触頻度が増大し、受精と耐久卵形成が促進された可能性がある

Dietary effect of selenium-fortified Chlorella vulgaris on reproduction of Brachionus plicatilis species complex (Rotifera: Monogononta)

We investigated the effects of fortifying a diet of Chlorella vulgaris with Selenium (Se) on sexual and asexual reproduction of rotifers in the Brachionus plicatilis species complex: i.e. two strains of B. plicatilis sensu stricto and one of Brachionus rotundiformis. These rotifers were cultured for 8?10 days on one of three different diets that were adjusted to provide the same dry weight of food: non-fortified Chlorella, Se-fortified Chlorella, and Nannochloropsis oculata. B. plicatilis (Makishima strain), which is obligatorily asexual, showed no difference in population growth rate among the three different diets (r?=?0.55?0.61). On the other hand, B. plicatilis (NH17L strain), which reproduces by cyclical parthenogenesis, showed higher population growth (r?=?0.25) and also higher rates of fertilization (35.9%) and absolute resting egg production (2803.9?eggs/g food) with the Se-fortified Chlorella diet than with other foods. Although B. rotundiformis (Kochi strain), which also exhibits cyclical parthenogenesis, showed no differences in population growth among the three different diets (r?=?0.42?0.48), sexual reproduction parameters were different depending on the feeding regime. The highest mixis (26.2%), fertilization (72.6%), and resting egg production (3489.9?eggs/g food) were observed with the Se-fortified Chlorella diet. We posit that the effect of Se-fortified diet was greater on the resting egg production by enhancing male fertility than on population growth