Hiromichi Imabayashi

Species composition and assemblage structure of chironomid larvae (Diptera: Chironomidae) attaching to the artificial substrates in a Japanese temperate basin, in relation to the longitudinal gradient

The relative importance of natural and anthropogenic factors, especially topographic type, riparian canopy, altitude, temperature and bank protection, on larval chironomid assemblage was investigated in a Japanese basin. To focus on the macro-scale factors, a concrete block, as an artificial substrate, was used for chironomid collection so that sampling regime may be identical among the sites. Partial CCA using sampling month as a covariable revealed that topographic type, riparian canopy coverage, water temperature and altitude were the main factors influencing species distribution. Stempellinella tamaseptima, Polypedilum tamanigrum and five Rheotanytarsus species showed positive, whereas five Cricotopus species showed negative associations with canopy coverage. Some traditional longitudinal zonations of species were still shown. Chironomus flaviplumus and Chironomus yoshimatsui were merely associated with lower reaches. Stepwise multiple regressions of the assemblage indices on the environmental variables were applied. Bank protection and depth showed negative correlations with Shannon diversity H′. Both topographic type and depth showed negative correlations with Pielou equitability J. Topographic type (lower reach) and specific conductance showed positive, while bank protection showed a negative correlation with abundance. Species richness was not explained by any variables. As a whole, topographic type was the most directly related factor to chironomid assemblages.

A new deep-water calanoid copepod and the phylogeny of the genus Nullosetigera nom. nov. in the Nullosetigeridae nom. nov. (pro Phyllopus: Phyllopodidae) from Japanese waters

Nullosetigeridae nom. nov. is proposed for Phyllopodidae Brodsky, 1950, nom. nud., and Nullosetigera nom. nov. is introduced for Phyllopus Brady, 1883, non Rafinesque, 1815. A new species, Nullosetigera auctiseta, is described from Japanese waters. Nullosetigera mutica comb. nov. (Sars, 1907) and N. mutata comb. nov. (Tanaka, 1964) are redescribed. Phylogenetic analysis implies that two groups, N. auctiseta–N. mutica group and N. mutata–N. impar–N. bidentata–N. helgae group, exist within the genus Nullosetigera and that the new species first diverges with N. mutica. The relatively advanced species, N. impar, N. bidentata, and N. helgae are the most widespread, and are vertically distributed from the epipelagic to the bathypelagic layers.

Variations in Body Size of the Lancelet Branchiostoma belcheri at Different Depths in the Seto Inland Sea: Effect of Food Supply on the Growth Rate

Abstract Variations in body size of the suspension-feeding lancelet Branchiostoma belcheri were examined from April 2001 to December 2001 at different water depths of 10–80 m. The lancelets were abundantly collected (220 indiv./dredge) at water depth of 10 m. The maximum size, ranging from 36.8 to 50.4 mm BL, decreased with increasing water depth. However, the minimum size of 7.4–7.8 mm BL, which corresponds to settling size, did not different with water depth. From seasonal changes in the length-frequency histograms, five cohorts were observed at every water depth. The lancelets grew to 44 mm BL at water depths of 10–20 m and to 34 mm BL at water depth of 80 m with four years of life span. Developmental stages of the gonads at an age of two years showed that no individuals had undeveloped gonads at water depth of 10 m, but 82% of them did at water depth of 80 m. The analysis of the stepwise multiple regressions of monthly growth rate on environmental variables showed that chlorophyll a was the best explanatory variable and showed a significant positive correlation with the growth of 1–2 years age groups. These results suggested that variations in the body length were mainly fluctuated by phytoplankton supply.

A new species of the genus Stempellinella (Diptera: Chironomidae) from Hiroshima, Japan

Stempellinella coronata sp. n. is described and illustrated based on male imagines. The new species can be separated from other Stempellinella species by its small size, low antennal ratio, high front leg ratio, minute frontal tubercles, a comparatively long median volsella, lacking median tergal setae, and lacking well-developed anal crests on the tergite IX. The generic diagnosis of Stempellinella is emended mainly to accommodate S. coronata. The species has so far been collected only from autumn to winter at pools in the unpolluted upper to mid reaches and was recorded first from the Ohta River system, Hiroshima, Japan.

Changes in body constituents of young red sea bream, Pagrus major, in reference to survival during experimental stocking

Abstract Two groups of fish produced under different systems were stocked for 61 days in a test pond without artificial feeding. The loss of body weight and muscle lipid during the stocking period corresponded to the characteristics of starved fish. Survival was 22.7% in group I and 8.7% in group II. The high survival of group I was deduced to be due to higher retention of reserved lipid. Although the stocking period raised some differences in fatty acid composition of muscle triglycerides, there was no marked difference in the composition between two groups.

Renewal of Genetic Composition of a Lancelet, Branchiostoma belcheri, in the Seto Inland Sea, Japan

Abstract We studied renewal of genetic composition of a lancelet, Branchiostoma belcheri, at a station in the Seto Inland Sea, Japan, using random amplified polymorphic DNA (RAPD) technique. We detected a total of 49 DNA bands from 27 individuals of 5 seasonal samples. Among these, some were specific to individual or seasonal sample. There were no bands common to all individuals. We calculated the Band Sharing Index (BSI) values for each combination of individuals. BSI was in a wide range of 0.00–0.97 and the average BSI between the individuals of a sample was remarkably different from sample to sample (0.37–0.83). In cluster analysis on the basis of BSI, largely 3 clusters were constructed, which finally connected to a single cluster at as low as about 0.2 of BSI. Besides, many clusters were constructed exclusively by a seasonal sample. These results suggest a large gene pool of lancelets in this area, the remarkable differences in gene pool size among the samples and a seasonal renewal of genetic composition at a habitat.

Genetic Relationships among Lancelet Populations in Seto Inland Sea Inferred from Mitochondrial DNA Sequences

Genetic relationships were examined among a total of 74 lancelets, Branchiostoma japonicum (Willey 1897), collected at 16 stations in the Seto Inland Sea on the basis of the sequence of the COI region of mitochondrial DNA. Genetic divergence was usually high at the stations near straits. Besides, there were no significant relationships between geographical and genetic distances of individual lancelets. As many as 62 haplotypes were recognized, among which only three comprised multiple individuals from distant stations, and the remaining ones comprised a single individual. In a dendrogram, some clusters were made up of individuals from nearby stations whereas other ones were made up of those from more or less distant stations. These results suggest that the high genetic heterogeneity of the lancelet population in the Seto Inland Sea is maintained by continuous genetic exchanges via a large-scale dispersion at long planktonic stages driven by tidal and constant currents in this region.

Estimation of geographical distribution limits between two subspecies of white-spotted charr, Salvelinus leucomaenis imbrius and S. l. pluvius, on the basis of RAPD analysis

RAPD分析に基づき，日本海流入河川のイワナ2亜種，ゴギとニッコウイワナに特異的な遺伝子型の分布を調べることにより，両者の分布境界を推定した。計16断片が増幅され，1個体から7-14バンドが検出されたが，ゴギあるいはニッコウイワナにのみ特異的なバンドは見られなかった。ゴギ，ニッコウイワナ各々9，15のハプロタイプが見られ，これらのうち，2タイプのみが両亜種共通であった。両者が混棲する可能性がある中間域では24ハプロタイプが見られ，これらのうち，5，9タイプがそれぞれゴギ，ニッコウイワナ特異的であった。ゴギ特異的タイプは鳥取県勝田川が東限，ニッコウイワナ特異的タイプは鳥取県日野川が西限であった。日野川水系では17ハプロタイプが見られ，それらのうち，3，7タイプがそれぞれゴギ，ニッコウイワナ特異的であった。クラドグラムではゴギあるいはニッコウイワナ特異的タイプのみからなる大きなクレードは形成されなかった。これらは，ゴギは東方へ，ニッコウイワナは西方へ分布を広げ，その際に大山山塊が両者にとって分布拡大の障壁となったことを示唆する。

Relationship between morphological and genetic trees of marine chironomid species

海産4属，Clunio，Semiocladius，TelmatogetonおよびThalassosmittiaと陸生のSmittia，淡水性のCricotopus属のエリユスリカ亜科と近縁亜科の形態学的系統樹と遺伝学的系統樹の関係を調べた。遺伝学的系統樹では3系統，すなわちSmittia，SemiocladiusとClunioを含む他の4属に分かれた。さらに，TelmatogetonとThalassosmittiaは別亜科にも拘わらず小さなクラスターを形成した。形態学的系統樹ではSemiocladiusとClunioは小さなクラスターを形成したが，TelmatogetonとThlassosmittiaはこれらだけではクラスターを形成しなかった。Cricotopusは最後に大きなクラスターに加わった。これらの結果は，Clunio，TelmatogetonとThalassosmittiaは淡水種の祖先から派生したこと，そして形態学的形質の中にいくらかの平行進化が存在することを示唆する。

Differences in allele frequency at ME-1 locus among four subspecies of Japanese white-spotted char Salvelinus leucomaenis

Four subspecies of a white spotted char, Salvelinus leucomaenis, are recognized to distribute in the Hokkaido and Honshu Islands of the Japanese Archipelagoes; S. l. leucomaenis (Amemasu), S. l. pluvius (Nikkoiwana), S. l. japonicus (Yamatoiwana) and S. l. imbrius (Gogi). The Amemasu has characteristic large white spots on the body side, the Yamatoiwana has rather faint reddish spots along the lateral line, the Gogi has conspicuous worm-like spots on the snout, whereas the Nikkoiwana comprizes of all these forms. However, the morphological distinctions and taxonomic stata, as well as distribution boundaries, were quite equivocal between the subspecies. Nakajima and Fujio stated that genetic distance among the four subspecies falls within the range of local populations according to the criteria by Nei. In this study, char samples from different regions of Japan, particularly the Chugoku Region, were subjected to allozyme analysis and genetic differentiation within and between local samples, as well as that within and between subspecies, was investigated. An isozyme, Malic enzyme (ME) was selected since a locus, ME-1*, has been reported to be polymorphic in S. leucomaenis and S. malma malma (Oshorokoma). Table 1 lists the lakes and rivers where char samples were collected, usually by bate fishing, at the upper reaches as possible for collecting native fish. The samples in Lake Shikotsu were kindly provided by Dr S. Urawa, National Salmon Resources Center, Japan. Char was killed by bleeding, measured for body sizes, and a small block of muscle was dissected with a surgical knife and stored at -80°C until use. Crude muscle extract was prepared, and starch gel electrophoresis was performed with ice-cooling, according to the methods described in Numachi. After electrophoresis at 15 mA for 90 min, the gel was sliced, stained with 50 mL of b-nicotinamide adenine dinucleotide phosphate (NADP) basic buffer (60 mg NADP and 40 mg nitro blue tetrazolium in 100 mL of distilled water), containing 1 mL of 1 M MgCl2 and a mixture of 500 mg sodium malate in 50 mL of 0.2 M Tris-Cl, pH 8.0, and photographed. A total of 216 fishes from 36 sites were collected between April 1997 and August 1999. Total length, body length and body weight were all in wide ranges, 8.8–30.8 cm, 7.3–26.4 cm and 5.3–208.8 g, respectively (Table 1). Two loci, ME-1* and ME-2*, were estimated in ME (Fig. 1). The locus ME-1* was polymorphic and three electrophoretic patterns were observed, each designated to genotypes *a/*a (homozygote), *a/*b (heterozygote) and *b/*b (homozygote). In contrast, the locus ME-2* was monomorphic. Therefore, ME-1* was selected for the analysis of genetic differences. Allele frequencies of ME-1* locus of all local samples are shown in Table 1. In the Sea of Japan side, *a allele was dominantly observed (0.909– 1.000) in 14 samples from Hokkaido (Lake Shikotsu), as far as the middle of the Chugoku Region (Hino River). However, more diversified allele frequency (*a ranging from0.000 to1.000)was found in eight samples from the western Chugoku Region (Hakuta River to Takatsu River). The fishes from these western Chugoku Region samples were morphologically designated as Gogi. Similar aspects were observed in the Pacific Ocean side. Nine samples, morphologically designated to be Nikkoiwana and Yamatoiwana, from the northern part of Honshu at the Pacific side (Natsui River), as *Corresponding author: Tel: 81-824-24-7894. Fax: 81-824-24-7916. Email: kawagogi@hiroshima-u.ac.jp Received 25 April 2005. Accepted 20 June 2006. FISHERIES SCIENCE 2007; 73: 1398–1400