Koichiro Kawai

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.

Occupational Allergy to Adult Chironomid Midges among Environmental Researchers

A case of occupational allergy to chironomid midges in research work is described. A researcher was exposed to adult chironomid midges during his research and developed allergic rhinitis after 10 years of such exposure. Using the midge extract of adult Chironomus plumosus (CP) (Linnaeus, 1758), both immediate skin test and the ophthalmic challenge test gave positive results. IgE antibody against adult CP was also demonstrated by the radioallergosorbent test. Four of the five serum samples of the environmental researcher examined showed a positive radioallergosorbent test to at least one of the adult midges breeding around eutrophic Japanese lakes. Enzyme-linked immunosorbent assay inhibition test and immunoblot experiments indicated that the remaining hemoglobin is one of the major allergens of adult CP. These results demonstrate that the exposure to adult chironomid midges is an important occupational hazard among environmental researchers.

Purification and characterization of an allergenic monomeric hemoglobin from a chironomid distributed worldwide, Polypedium nubifer

The Pol n component MV, a potent experimental allergen for mice, was purified to homogeneity from extracts of a chironomid distributed worldwide, Polypedium nubifer (PN). The Pol n I component MV was shown to have cross-reactivity to hemoglobins (Hb) derived from all species of chironomids tested. Determination of the amino acid sequence of the first 37 N-terminal residues revealed that it had 30-59% homology to Hb of an European chironomid, Chironomus thummi thummi, which had been known as an important allergen for humans. By Western blot analysis, we showed that sera from asthmatic patients, which had positively reacted to the extract of the adult PN midge, bound to the purified Pol n I component MV. Furthermore, using rabbit polyclonal antibodies raised against synthetic polypeptides corresponding to the N-terminal residues, it was demonstrated that the N-terminal amino acid sequence between position 15 and 35 contained antigenic epitope(s) for human IgE. The results indicate that the Pol n I component MV is an allergen for human beings as well as for mice, and useful as a diagnostic tool for chironomid allergy.

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.

New host record for Argulus coregoni (Crustacea: Branchiura: Argulidae), with discussion on its natural distribution in Japan

An adult male of Argulus coregoni Thorell, 1864 was collected from the skin of a gogi charr Salvelinus leucomaenis imbrius Jordan and McGregor (Salmoniformes: Salmonidae) in the uppermost reaches of the Takatsu River in Yoshiga, Shimane Prefecture, Japan. This finding represents the first record of A. coregoni from western Japan. Salvelinus leucomaenis imbrius is a new host for A. coregoni. This salmonid is endemic to rivers in part of the Chugoku Region, western Japan, and small isolated populations of the fish occurred at the sampling sites. No other salmonids had been stocked there. These facts indicate that A. coregoni is native to the river which does not support the view put forward in the 1960s that A. coregoni had been probably introduced from Europe into Japan.

Temporal and Spatial Dynamics of a Lower-Intertidal Lancelet Population in the Seto Inland Sea, Japan

The population dynamics of Branchiostoma japonicum, formerly known as B. belcheri, were investigated from September 2003 to August 2005 in the intertidal zone at Takehara (Hiroshima Prefecture), Seto Inland Sea, Japan. The intertidal population appeared from spring to autumn and disappeared during winter. A laboratory experiment showed that exposure to temperatures below 1°C for 2 hours resulted in severe mortality. This low temperature corresponds to the minimum temperature in sediments in the study area. This result suggested either that the intertidal population collapses in winter because of low temperature, or that the lancelets escape from the intertidal to the subtidal zone. Throughout the research period, no lancelets smaller than 10 mm in body length were found, indicating that no larvae settled in the intertldal zone. The intertldal population is probably maintained by the influx of individuals from the neighboring subtidal population. The mean annual density of the lancelets was greatest (10.6 individuals/m2) at station 1 nearest the low water mark, and lowest (0.3 Individuals/m2) at station 3 furthest from the low water mark. In summer, the water content of the sediments was remarkably lower at station 3 (20.2%) than at station 1 (25.8%). Another laboratory experiment showed that higher mortality occurred from exposure to sediments with a water content less than 25% for 2 hours, comparable to the water content at station 3, suggesting that the spatial distribution of the lancelets upward in the intertidal is restricted by sediment dryness.

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.

Gene cloning of a monomeric hemoglobin of a widely distributed chironomid Polypedilum nubifer

A gene of a monomeric hemoglobin, the Pol n component of MV, of a chironomid species, Polypedilum nubifer, was cloned by screening the larval cDNA library with a nucleotide probe corresponding to the N-terminal sequence of purified MV. A clone, 8N, was 755 bp long and comprised a 60 bp 5′ non-coding region, a 209 bp 3′ non-coding region and a 486 bp coding region for 160 amino acids. A comparison of N-terminal sequence of purified MV with that estimated from the DNA sequence of clone 8N, revealed the existence of a signal peptide consisting of 14 residues. This signal peptide was almost exclusively composed of hydrophobic amino acids, suggesting the peptide functions in preglobin transport across the endoplasmic reticulum. The estimated sequence of mature globin of MV showed only 41% of homology to that of CTT-IV, a chromatographically similar monomeric Hb to MV, of an another chironomid species, Chironomus thummi thummi, in a 146 alignment. However, displacements in hydrophilic ⇆hydrophobic manner were observed only at 28 positions whereas those in hydrophobic ⇆hydrophobic or hydrophilic ⇆hydrophilic manner were observed at 45 positions. Furthermore, a comparison of the haem contact positions between these two Hbs showed a remarkable conservance and displacements only in hydrophilic ⇆ hydrophilic or hydrophobic ⇆hydrophobic manner, suggesting the crucial role of these positions in Hb functionality.

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.