A low trophic position of Japanese eel larvae indicates feeding on marine snow

What eel larvae feed on in the surface layer of the ocean has remained mysterious. Gut contents and bulk nitrogen stable isotope studies suggested that these unusual larvae, called leptocephali, feed at a low level in the oceanic food web, whereas other types of evidence have suggested that small zooplankton are eaten. In this study, we determined the nitrogen isotopic composition of amino acids of both natural larvae and laboratory-reared larvae of the Japanese eel to estimate the trophic position (TP) of leptocephali. We observed a mean TP of 2.4 for natural leptocephali, which is consistent with feeding on particulate organic matter (POM) such as marine snow and discarded appendicularian houses containing bacteria, protozoans and other biological materials. The nitrogen isotope enrichment values of the reared larvae confirm that the primary food source of natural larvae is consistent only with POM. This shows that leptocephali feed on readily available particulate material originating from various sources closely linked to ocean primary production and that leptocephali are a previously unrecognized part of oceanic POM cycling.     

Possible adaptive and non-adaptive radiation in three plant genera in the Japanese archipelago

The adaptive radiation of flowering plants as manifested by the floral diversity has long been considered associated with the diversity of plant–pollinator interactions, because changes in plant–pollinator interactions are hypothesized as one of the major mechanisms driving plant ecological speciation. To understand the relative contributions of various mechanisms for plant radiation, including pollinator changes, it is useful to study a plant group for which comparative study of the species life history across the whole lineage is feasible. To this end, we will focus on the plant lineages that have presumably radiated in the Japanese archipelago, namely, the genera Asimitellaria, Asarum, and Arisaema. By comparing these three genera, we will comment on the possible modes of adaptive radiation and diversification among the endemic flora of Japan.     

HLA class II alleles in Ainu living in Hidaka district,Hokkaido, northern Japan

The Ainu people are considered to be the descendants of preagricultural native populations of northern Japan, while the majority of the population of contemporary Japan (Wajin) is descended mainly from postneolithic migrants. Polymorphisms of the HLA-DRB1, DRB3, and DQB1 alleles were investigated in DNA samples of 50 Ainu living in Hidaka district, Hokkaido. Unique features of the Ainu in this study were high incidences of DRB1*1401, DRB1*1406, and a newly described allele, DRB1*1106 (20%, 17%, and 5%, respectively). On the other hand, several common alleles in Wajin (DRB1*1502, 1302, 0803, and 1501) were found at relatively low frequencies (1–2%) in Ainu. Previously DRB1*1406 was described as a characteristic allele of some Native American or northeast Asian ethnic groups, and DRB1*1106 had been found in only two Singapore Chinese and one Korean. Principal component analysis of various populations based on HLA class II allele frequencies places the Ainu population midway between other east Asian populations, including Wajin, and Native Americans. These observations may support the hypothesis that the Ainu people are the descendants of some Upper Paleolithic populations of northeast Asia from which Native Americans are also descended. © 1996 Wiley-Liss, Inc.     

Ecophysiological responses of Japanese forest tree species to ozone, simulated acid rain and soil acidification

In this review, I summarized the results obtained from experimental studies on the ecophysiological responses of Japanese forest tree species to O₃, simulated acid rain and soil acidification. Based on the studies conducted in Japan, exposure to ambient levels of O₃ below 100 nl·l⁻¹ (ppb) for several months is sufficient to inhibit dry matter production and net photosynthesis of sensitive Japanese forest tree species such as Siebold's beech and Japanese zelkova. On the other hand, exposure to simulated acid rain with a pH of 4.0 or above for several months cannot induce any adverse effects on dry matter production and physiological functions of Japanese forest tree species. However, when the pH of simulated rain or fog is lowered below 4.0, negative effects appear on dry matter production and physiological functions such as transpiration in several sensitive Japanese forest tree species such as Japanese fir and Nikko fir. Based on limited information, it may be concluded that (1) Al dissolved into soil solution is the most important limiting factor for dry matter production, physiological functions and nutrient status of Japanese forest tree species grown in acidic soil, (2) the (Ca+Mg+K)/Al molar ratio in soil solution is a useful indicator to evaluate and predict the effects of soil acidification due to acid deposition on whole-plant dry matter production of Japanese forest tree species at the present time and in the future, and (3) Japanese coniferous tree species such as Japanese cedar and red pine are relatively sensitive to a reduction in (Ca+Mg+K)/Al molar ratio in soil solution compared with European forest tree species such as Norway spruce.     

Addition and re-examination of Japanese species belonging to the genus <Emphasis Type="Italic">Cercospora </Emphasis>and allied genera. V. Collections from the Nansei Islands (2)

 Five species collected in the Nansei Islands are discussed. Of these, one species found on Gardenia jasminoides is described as a new species, Cercosporidium okinawaense Kobayashi et Nishijima. Asperisporium caricae on Carica papaya, Pseudocercospora melastomobia on Melastoma candidum, and P. neoliquidambaris Nakashima et Kobayashi, nom. nov. on Liquidambar formosana are newly added to the Japanese mycoflora. Cercospora violamaculans on Rhaphiolepis umbellata is transferred to the genus Pseudocercospora as Pseudocercospora violamaculans (Fukui) Kobayashi et Nakashima, comb. nov., with some additional notes. Received: October 26, 2001 / Accepted: March 13, 2002     

State-space modeling clarifies productivity regime shifts of Japanese flying squid

Regime shifts of climatic and environmental conditions potentially affect the productivity of fishery resources, posing challenges in stock management. The stocks of the Japanese flying squid (Todarodes pacificus) are suspected to suffer from regime shifts, but detecting the occurrence of regime shifts in this species is generally difficult and unreliable because the short-lived nature of this species inherently confounds the effect of regime shifts with observation and process errors. Here we developed a new state-space assessment model to evaluate the influence of regime shifts on the spawner-recruit relationship of the Japanese flying squid. The model simultaneously estimates the population dynamics of multiple stocks that could share some life history parameters, thereby stabilizing parameter inference. We demonstrate that two regime shifts in productivity around 1991 and 2015 caused two- to threefold changes of maximum sustainable yields. The model with regime shifts clarifies the relationship between fishing pressure and spawner abundance that is difficult to detect in a model with no regime shift. The state-space approach is a promising tool for accurately assessing stock status by separating the recruitment process from observation errors and is expected to contribute to the effective management of marine biological resources sensitive to regime shifts.     

Optimization of protocols for microinjection-based delivery of cryoprotective agents into Japanese whiting Sillago japonica embryos

Microinjection has proven useful for introduction of low-permeability cryoprotective agents (CPAs) into fish eggs or embryos for cryopreservation. In this work, we examined the suitable conditions for single or combined microinjection into the perivitelline space (PS) and the yolk mass (YM) of embryos of the Japanese whiting, an alternative marine fish model for embryo cryopreservation studies. The parameters examined were injection volume, CPA type and concentration, vehicle (diluent), and suitable developmental stage. Somites and tail elongation embryos tolerated single or combined injection with 2.1 and 15.6 nl in the PS and YM, respectively, whereas earlier embryonic stages tolerated only up to 8.2 nl in the YM. The injected solutions diffused rapidly throughout the PS and YM and remained contained within each compartment unless in the case of structural damage caused by injection of larger volumes. Yamamoto solution was marginally better as a vehicle for microinjection of CPAs than fish Ringer and phosphate buffer saline whereas ¼ artificial sea water was clearly unsuitable. Ethylene glycol was well tolerated by embryos in all developmental stages whereas 1, 2-propylene glycol was suitable only for early embryonic stages. Overall, microinjection was efficient in delivering high loads of CPAs inside whiting embryos more swiftly than previously obtained for this species by immersion-based impregnation protocols. Embryos microinjected with CPAs showed a decrease in embryo nucleation temperature and an increase in chilling tolerance. CPA-microinjected embryos will provide valuable materials to optimize the remaining parameters that are critical for successful cryopreservation such as cooling and warming strategies.     

Freeze-fracture study of the lateral-line canal organ of the Japanese sea eel,Lincozymba nystromi

Summary Specializations of apical surfaces of hair cells, supporting cells and marginal cells in the lateral-line canal organ of Japanese sea eel, Lincozymba nystromi, were examined with a freeze-fracture technique. Apical surfaces of hair cells have a lower density of intramembrane particles (IMP) than those of the surrounding supporting cells. Density of IMP on the streocilia is almost the same as that on the apical surface of hair cells. Junctions between hair and supporting cells were tighter than those between two supporting cells; those between supporting and marginal cells were tighter than those between hair and supporting cells, and those between two marginal cells were the tightest in the lateral-line canal organ.     

Monoamine fluorescence in the median eminence of the Japanese quail,Coturnix coturnix japonica,following medial basal hypothalamic deafferentation

Summary Monoamine fluorescence was examined in the ventral hypothalamus of the Japanese quail, Coturnix coturnix japonica after medial basal hypothalamic deafferentation. In sham-operated control birds, numerous yellow-green fluorescent fibers were observed in the median eminence and the nucleus tuberis. In the area of the paraventricular organ, a number of fluorescent fibers and cell bodies were observed. In birds with deafferented hypothalami, fluorescence disappeared both in the median eminence and the nucleus tuberis. In the area of the paraventricular organ, which was within the area of deafferentation, fluorescence of neuronal perikarya did not change, but fluorescent fibers decreased markedly in number. Disappearance of monoamine fluorescence in the median eminence and the nucleus tuberis is discussed in relation to the tanycyte absorptive function and gonadal development.Supported by Grants from the Ministry of Education to Professors T. Bando and H. Kobayashi, and a Grant from the Ford Foundation to Prof. H. Kobayashi.