Biology ofChironomus piger Str. (Diptera: Chironomidae) and its role in the self-purification of a river

Chironomus piger larvae are widespread in small rivers and canals strongly polluted with domestic sewage. Despite this, almost nothing is known concerning the biology of the species under natural conditions and its role in the process of river self-purification. For two years, benthic samples were collected in the Sestra River at a site about 250 m downstream of the effluent discharge drains of a sewage treatment installation where the greatest concentrations of the larvae occurred. The number and biomass ofC. piger larvae were subject to marked fluctuations,viz. 96,000–348,000 ind m^–2 and 420–1,800 g m^–2. 460 degreedays (on average) was required for development of one generation.C. piger has 5 or 6 generations per year depending on the hydrometeorological conditions during the growing season.C. piger larvae play an important role in self-purification of the river. They utilize precipitating seston for food and for building their dwelling tubes. According to our calculations the amount of organic matter assimilated in the area of maximum larval concentration ranged 80–177 g wet weight m^–2 day^–1, and 32–71 g wet weight m^–2day^–1 was mineralized.     

Effects of dimethylsulfoxide on the ultrastructure of fixed cells

It has been reported that the use of dimethylsulfoxide (DMSO) as a solvent for fixatives enhances preservation of cellular ultrastructure. By contrast, we have shown that DMSO alters the ultrastructural integrity of glutaraldehyde fixed cells. The cell membrane, nuclear envelope, endoplasmic reticulum, ribosomes, microtubules and intracytoplasmic organelles are most susceptible to the action of DMSO. We hypothesize that DMSO exerts intracellular alterations via its interaction with remnant interfacial water in fixed cells. DMSO-induced alterations of these and related cellular components may result in the formation of artefactual structures and networks. Thus, it appears that DMSO containing glutaraldehyde neither accelerates fixation nor enhances stabilization of cellular ultrastructure. For these reasons, addition of DMSO to fixatives is not recommended.     

Trophic interactions in the system host (eelpout Lota lota)—Parasite (Eubothrium rugosum)—Symbiotic microflora at hydrolysis of carbohydrate food components

It is established that bacteria with the ability to produce enzymes hydrolyzing carbohydrates of different complexity degrees are associated with the intestine digestive-transport surfaces of the eelpout Lota lota (L.) and of cestoids Eubothrium rugosum parasitizing in it. The release by bacteria of enzymes hydrolyzing not only complex carbohydrates, but also disaccharides, decreases the energy expenditures of the host and parasite for synthesis of their own hydrolases and increases the glucose concentration near the transport surfaces, which allows all members of this formed community to use glucose. The total amylolytic activity (TAA) of enzymes and the α-amylase activity of the studied bacteria are realized in a wide range of pH values. The levels of the enzyme general amylolytic activity and of bacterial α-amylase activity under the experiment conditions are comparable with similar characteristics of enzymes desorbed from the studied surfaces and participating in the membrane digestion processes in the host and parasite, which can suggest a significant contribution of the symbiotic microflora enzymes to digestion of the host and parasite.     

Hydrolytic activity of enzymes produced by symbiotic microflora and its role in digestion processes of bream and its intestinal parasite Caryophyllaeus laticeps (Cestoda, Caryophyllidea)

Bacteria capable to secrete enzymes hydrolyzing proteins and carbohydrates proved to be associated with the digestive-transport surfaces of the bream intestine and tegument of cestode Caryophyllaeus laticeps. Apparently, the contribution of symbiotic digestion to the hydrolysis of polymers increases during active feeding of fishes, while at low feeding rate, bacteria can compete with the host and its parasite for the available monomers. Secretion of bacterial enzymes hydrolyzing both complex carbohydrates and disaccharides reduces the metabolic expenditures of the macroorganisms for the synthesis of their own hydrolases. Glucose resulting from hydrolytic activity of bacterial enzymes can be used by all members of the established community. While bacteria colonizing the digestive-transport surfaces of the host and parasite were generally similar, some specific features were also observed probably due to the structural peculiarities of the intestinal mucosa and cestode tegument.     

Seventy‐five EST‐linked Atlantic salmon (Salmo salar L.) microsatellite markers and their cross‐amplification in five salmonid species

An Atlantic salmon (Salmo salar L.) expressed sequence tag (EST) database consisting of 58 146 ESTs was screened for microsatellite sequences. Subsequent development of 75 polymorphic EST‐associated microsatellite markers in this species is described together with cross‐species amplification results of 133 gene‐associated tandem repeat markers in five salmonid species (Salmo trutta, Oncorhynchus mykiss, Salvelinus aplinus, Thymallus thymallus, Coregonus lavaretus). The number of alleles among EST‐linked microsatellites in Atlantic salmon ranged from two to 41 with an average of 12 alleles per locus. Cross‐species amplification resulted in detection of a total of 111 polymorphic locus‐species combinations (12–32 loci per species).     

Final stages of carbohydrate metabolism in a cestode Eubothrium rugosum (Cestoda: Pseudophyllidea)

Characteristics of final stages of carbohydrate metabolism in a cestode Eubothrium rugosum from the burbot intestine have been studied. It is found out that in the course of in vitro incubation the worms produce lactic acid to the environment with a concomitant acidification of the medium. The rate of pH changes and lactate production eventually fell during the incubation. The medium pH being the result of helminth's metabolism varies within the normal physiological limits of the host intestine pH and pH optima for its basic digestive enzymes.     

Contrasting levels of genetic diversity between the common, self-compatible Liparis kumokiri and rare, self-incompatible Liparis makinoana (Orchidaceae) in South Korea

Levels of allozyme variation and intrapopulation spatial genetic structure of the two terrestrial clonal orchids Liparis kumokiri , a self-compatible relatively common species, and L. makinoana , a self-incompatible rare species, were examined for 17 ( N  = 1875) and four ( N  = 425) populations, respectively, in South Korea. Populations of L. makinoana harboured high levels of genetic variation ( H _e = 0.319) across 15 loci. In contrast, L. kumokiri exhibited a complete lack of allozyme variation ( H _e = 0.000). Considering the lack of genetic variability, it is suggested that current populations of L. kumokiri in South Korea originated from a genetically depauperate ancestral population. For L. makinoana , a significant deficit of heterozygosity (mean F _IS = 0.198) was found in population samples excluding clonal ramets, suggesting that pollen dispersal is localized, generating biparental inbreeding. The significant fine-scale genetic structuring (≤ 2 m) found in a previous study, in addition to the moderate levels of population differentiation ( F _ST = 0.107) and the significant relationship between genetic and geographical distances ( r  = 0.680) found here, suggests a leptokurtic distribution of seed dispersal for L. makinoana . Although populations of L. makinoana harbour high levels of genetic variation, they are affected by a recent genetic bottleneck. This information suggests that genetic drift and limited gene flow could be the main evolutionary forces for speciation of a species-rich genus such as Liparis .  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 153 , 41–48.