Long-term fluctuations in mollusk populations before and after the appearance of the alien predator <Emphasis Type="Italic">Euspira fortunei</Emphasis> on the Tona coast,Miyagi Prefecture,northern Japan

The impact of Euspira fortunei as an alien predator on fluctuations in population densities of prey mollusks between 2001 and 2010 on the Tona coast, northern Japan, was investigated. This species increased dramatically from 2002 to 2004. In contrast, prey species such as Ruditapes philippinarum and Macoma incongrua decreased rapidly from 2001 to 2004, whereas Pillucina pisidium and Batillaria cumingii did not show a significant decrease during this period. Using a laboratory experiment, we were able to show that these decreases in the population densities of some species of mollusks but not other species were the result of species-selective predation by E. fortunei, as the experiment revealed that E. fortunei preferred to attack R. philippinarum and M. incongrua rather than P. pisidium, although the predator did expand its diet to include P. pisidium after it had consumed 16 of the 20 preferred prey available (i.e., R. philippinarum and M. incongrua). This case study suggests that invasive naticid predators have the potential to affect the population density and community structure of prey mollusks in recipient coastal ecosystems through predation.     

Assessment of spermatogenesis and plasma sex steroids in a seasonal breeding teleost: a comparative study in an area of influence of a tributary, downstream from a hydroelectric power dam, Brazil

River damming and building of hydroelectric power plants interrupt the reproductive migration routes and change the major physicochemical parameters of water quality, with drastic consequences for populations of migratory fishes. The goal of this study was to evaluate proliferation and cell death during spermatogenesis and serum profiles of sex steroids in Prochilodus argenteus, from the S?o Francisco River, downstream from the Três Marias Dam. A total of 257 adult males were caught quarterly during a reproductive cycle in two sites: the first 34?km of the river after the dam (site 1) and the second 34–54?km after the dam (site 2), after the confluence with a tributary, the Abaeté River. Seasonal changes in the testicular activity associated with morphometric analyses of germ cells as well as proliferation and testicular apoptosis support a more active spermatogenesis in fish from site 2, where higher levels of sex steroids and gonadosomatic index (GSI) were also found. In site 1, fish presented low serum levels of testosterone, 17β-estradiol and 17α-hydroxyprogesterone and a low GSI during gonadal maturation. Spermatogonial proliferation (PCNA) and apoptosis (TUNEL) were more elevated in fish from site 1, but spermatocytes were mainly labelled in fish from site 2. Overall, these data demonstrate changes in testicular activity and plasma sex steroids in a neotropical teleost fish living downstream from a hydroelectric dam, supplying new data on fish reproduction in regulated rivers. Moreover, morphometric analyses associated with sex steroids profiles provide reliable tools to assess fish spermatogenesis under environmental stress conditions.     

Digital image analysis and chlorophyll metering for phenotyping the effects of nodulation in soybean

Leaf photosynthesis and rhizobial nitrogen fixation are the two metabolic processes of utmost importance to legume growth and development. As these processes are closely related to each other, measuring of leaf chlorophyll content can provide information on the nodulation and nitrogen fixation status of crop plants. In the present investigation, a number of soybean breeding lines consisting of near-isogenic families which are genetically segregating for the nodulation trait were utilized in field experiments carried out across three growing seasons at Vienna, Austria. For phenotyping leaf chlorophyll content, the Minolta SPAD spectrometer was applied in parallel to a simple leaf digital image analysis procedure based on a commercial digital still camera. The main objectives of the research included the comparison of SPAD metering and image analysis for determination of chlorophyll content, phenotyping of the soybean nodulation vs. non-nodulation characteristic with respect to leaf, agronomic and seed traits, and relating both chlorophyll and image analysis data to seed quality characteristics. Nodulating and non-nodulating soybean lines significantly differed in chlorophyll content from the V5 (five leaves fully developed) soybean developmental stage onwards. Apart from chlorophyll content, leaf size, plant height, number of pods per plant, 1000-seed weight, and seed protein and oil content were also affected by nodulation type. The chlorophyll content of soybean leaves as determined by SPAD metering was significantly correlated (r = −0.937) to the green color value (RGB color model) of leaf image analysis at the R3 (beginning of pod growth) soybean developmental stage. Both chlorophyll content and leaf image analysis parameters were correlated to 1000-seed weight, seed protein and seed oil content. Thus, it appears that these leaf parameters related to photosynthesis and nitrogen fixation could be utilized to determine the nitrogen status of a soybean crop and subsequently in forecasting seed quality parameters of the harvest product.     

Fish assemblages in headwater tributaries of the Agano River System,Japan

The present study examined fish assemblages in ten tributaries with different environmental characteristics in the upper drainages of the Agano River system, northern Honshu, Japan. Seven fish species (five families) were found in the 10 tributaries examined. White-spotted charr Salvelinus leucomaenis and sculpin Cottus pollux were common in almost all tributaries. Masu salmon Onchorhynchus masou masou inhabited the tributaries at relatively low densities despite intensive stocking in the study region. No statistically significant relationships between local environmental factors and the number of species captured were found. However, all seven species, including age-0 fish of each species, were recorded in the tributary with the lowest gradient and second-narrowest stream width, suggesting that small tributaries potentially provide an important habitat for a diverse range of species. The relative density of white-spotted charr in tributaries subject to fishing prohibition was higher on average than that in tributaries not subjected to fishing prohibition, suggesting that fishing depresses the abundance of white-spotted charr.     

Characterization of differentially expressed genes in liver in response to the rearing temperature of rainbow trout Oncorhynchus mykiss and their heritable differences

To characterize thermal-responsive genes in fish, firstly, juvenile rainbow trout were reared in four different temperature conditions (average temperatures were 10, 14, 18, and 22 °C, respectively) and differentially expressed genes were identified. Gene expression in the liver was analyzed by the differential display method, followed by validation using real-time PCR. Subsequently, to examine whether the identified genes show heritable differences, the gene expression levels were compared among juveniles of three genetically distinct lines of rainbow trout (a strain and two closed colonies) by rearing at two different temperature conditions (average 14 and 22 °C). By rearing at 22 °C, growth retardation was observed compared with fish reared at 14 and 18 °C, and six genes were identified as differentially expressed genes in response to the rearing temperature in the gene expression analyses. With the increase in rearing temperature, gene expressions of a complement C1q and two ribosomal proteins were significantly up-regulated. On the other hand, three metabolic genes (betaine homocysteine methyltransferase, triosephosphate isomerase, and glucose-6-phosphatase) were down-regulated, indicating a metabolic depression due to high temperature. In the subsequent analyses, in response to the rearing temperature (14 and 22 °C), there was a trend that the complement C1q and glucose-6-phosphatase genes showed different expression patterns among the three rainbow trout lines, suggesting heritable differences in these genes. Our study provides information on thermal-responsive genes in fish, and we anticipate it will facilitate further investigation in the thermal biology of fish.     

Biosynthesis of Akaeolide and Lorneic Acids and Annotation of Type I Polyketide Synthase Gene Clusters in the Genome of Streptomyces sp. NPS554

The incorporation pattern of biosynthetic precursors into two structurally unique polyketides, akaeolide and lorneic acid A, was elucidated by feeding experiments with ¹³C-labeled precursors. In addition, the draft genome sequence of the producer, Streptomyces sp. NPS554, was performed and the biosynthetic gene clusters for these polyketides were identified. The putative gene clusters contain all the polyketide synthase (PKS) domains necessary for assembly of the carbon skeletons. Combined with the ¹³C-labeling results, gene function prediction enabled us to propose biosynthetic pathways involving unusual carbon-carbon bond formation reactions. Genome analysis also indicated the presence of at least ten orphan type I PKS gene clusters that might be responsible for the production of new polyketides.     

Monitoring by real-time PCR of three water-borne zoosporic Pythium species in potted flower and tomato greenhouses under hydroponic culture systems

The high-temperature-tolerant Pythium species P. aphanidermatum, P. helicoides, and P. myriotylum cause serious diseases in many crops under hydroponic culture systems in Japan. Control of the diseases is difficult because these zoosporic pathogens spread quickly. In this study, a real-time PCR method was developed for monitoring the spread of zoospores of the three pathogens. Specific primers and TaqMan probes were established using the internal transcribed spacer regions of the rDNA. Specificity was confirmed using known isolates of each species and closely related non-target species. The sensitivity of DNA detection was 10 f. for each pathogen. 10 f. DNA corresponded to 4 P. aphanidermatum, 3 P. myriotylum, and 4 P. helicoides zoospores, respectively. Therefore, this real-time PCR method was used to evaluate and monitor zoospores in the nutrient solutions of ebb-and-flow irrigation systems for potted flower production and closed hydroponic culture systems for tomato production. The results indicated that the pathogens were present in the hydroponic culture systems throughout the year, and spread before disease occurrence.     

Seedling blight of Glycyrrhiza uralensis caused by Pythium myriotylum,P. aphanidermatum and P. spinosum and identifying primary inoculum sources using multiplex PCR detection

Pythium species, isolated from seedlings of Glycyrrhiza uralensis with blight, were identified as P. myriotylum, P. aphanidermatum, and P. spinosum on the basis of morphological characteristics and sequences of the internal transcribed spacer regions of rDNA. In pathogenicity tests, the isolates of the three Pythium species caused blight, producing the original disease symptoms. The primary inoculum source was determined using a multiplex PCR to detect the pathogen. All the Pythium species were detected in the soils of fields with the diseased plants and in soils of adjacent field soils.     

Molecular taxonomy and its application to ecological studies of Pythium species

More than 140 Pythium species have been described; 41 of these species have been described since 2000. Many Pythium species cause seed rot and damping off of seedlings. Recent changes in crop culture systems, such as the introduction of hydroponic cultures, have resulted in Pythium diseases of mature plants as well, with symptoms such as root rot, crown rot, and blight. In Japan, newly introduced ornamental and floral plants are vulnerable to high temperatures and humidity, resulting in severe Pythium infections. Once a pathogen invades a greenhouse, it quickly propagates and disperses, resulting in serious yield loss. It is very difficult to identify an isolate at the species level based on morphological characteristics because of overlaps in the size and shape of reproductive structures, heterothallism, and the continuing discovery of new species. New procedures based on DNA sequences have thus been introduced to identify species; in particular, the rDNA ITS region and the coxI gene have been recommended for DNA barcoding. BLAST searches and phylogenic analyses allow for easy and precise identification. PCR techniques are also being used to diagnose plant diseases, and real time PCR can be used for quantifying the pathogen to assess the risk of disease loss. Molecular techniques to analyze population structure help clarify transmission routes of pathogens and the ecology of Pythium flora in natural ecosystems. In this review we discuss recent advances in molecular methods for identifying, detecting, and classifying Pythium species.