Infections by helminth parasites in "puyenes", Galaxias maculatus (Galaxiidae, Salmoniformes), from Southern Argentina with special reference to Tylodelphys barilochensis (Digenea, Platyhelminthes).
The occurrence of Tylodelphys barilochensis, Acanthostomoides apophalliformis, Contracaecum sp. and Camallanus corderoi infecting Galaxias maculatus ("puyenes") was quantified for the first time in Lake Nahuel Huapi, southern Argentina. T. barilochensis was recorded in this lake for the first time. The role of G. maculatus population in transmission of parasites to the salmonids is more important for Contracaecum sp. (prevalence 14-34%) and A. apophalliformis (prevalence 30-54%) than for C. corderoi (prevalence 6-8%). The absence of Diphyllobothrium spp. in samples shows that the G. maculatus population does not play any role in the life cycles of these important zoonotic parasites. The sex of the host had no effect on T. barilochensis abundance. Statistical differences in T. barilochensis abundance between "puyenes" of the same size class between sampling stations and positive correlation between prevalence of infected snails and T. barilochensis abundance in fish suggest that different stocks have been sampled. Factors influencing T. barilochensis abundance are discussed. (+info)
Molecular evolution of transferrin: evidence for positive selection in salmonids.
Transferrins are iron-binding proteins that are involved in iron storage and resistance to bacterial disease. Previous work has shown that nonsynonymous-to-synonymous-site substitution ratios (d(n)/d(s) ratios) between transferrin genes from some salmonid species were significantly greater than 1.0, providing evidence for positive selection at the transferrin gene. The purpose of the current study was to put these earlier results in a broader evolutionary context by examining variation among 25 previously published transferrin sequences from fish, amphibians, and mammals. The results of the study show that evidence for positive selection at transferrin is limited to salmonids-d(n)/d(s) ratios estimated for nonsalmonid lineages were generally less than 1.0. Within the salmonids, approximately 13% of the transferrin codon sites are estimated to be subject to positive selection, with an estimated d(n)/d(s) ratio of approximately 7. The three- dimensional locations of some of the selected sites were inferred by comparing these sites to homologous sites in the bovine lactoferrin crystallographic structure. The selected sites generally fall on the outside of the molecule, within and near areas that are bound by transferrin-binding proteins from human pathogenic bacteria. The physical locations of sites estimated to be subject to positive selection support previous speculation that competition for iron from pathogenic bacteria could be the source of positive selection. (+info)
Euteleost fish genomes are characterized by expansion of gene families.
The presence of additional hox clusters in the zebrafish has led to the hypothesis that there was a whole genome duplication at the origin of modern fish. To investigate the generality of this assumption, we analyzed all available actinopterygian fish gene families, and sequenced nuclear receptors from diverse teleost fish. The origin and timing of duplications was systematically determined by phylogenetic analysis. More genes are indeed found in zebrafish than in mouse. This abundance is shared by all major groups of euteleost fish, but not by eels. Phylogenetic analysis shows that it may result from frequent independent duplications, rather than from an ancestral genome duplication. We predict two zebrafish paralogs for most mouse or human genes, thus expressing a note of caution in functional comparison of fish and mammalian genomes. Redundancy appears to be the rule in fish developmental genetics. Finally, our results imply that the outcome of genome projects cannot be extrapolated easily between fish species. (+info)
Structural and functional characterization of a C-type lectin-like antifreeze protein from rainbow smelt (Osmerus mordax).
Antifreeze proteins (AFPs) are produced by several cold-water fish species. They depress physiological freezing temperatures by inhibiting growth of ice crystals and, in so doing, permit the survival of these fish in seawater cooler than their normal freezing temperatures. The type II AFP from rainbow smelt (Osmerus mordax), which is a member of the C-type lectin superfamily, was characterized in terms of its Ca2+-binding quaternary structure and the role of its single N-linked oligosaccharide. The protein core of the smelt AFP, shown through sequence homology to be a C-type lectin carbohydrate-recognition domain, was found to be protease resistant. Smelt AFP was also shown to bind Ca2+, as determined by ruthenium red staining and a conformational change on Ca2+ binding detected by intrinsic fluorescence. The N-linked oligosaccharide was found to have no effect on protease resistance, dimerization, or antifreeze activity. Thus its role, if any, in the antifreeze function of this protein remains unknown. Smelt AFP was also shown to be a true intermolecular dimer composed of two separate subunits. This dimerization did not require the presence of N-linked oligosaccharide or bound Ca2+. Smelt AFP dimerization has implications for the effective solution concentration and measurement of its activity. This finding may also lead to new interpretation of the mechanism of ice-growth inhibition by this AFP. (+info)
The freeze-avoidance response of smelt Osmerus mordax: initiation and subsequent suppression of glycerol, trimethylamine oxide and urea accumulation.
Smelt (Osmerus mordax) were maintained at either ambient water temperature or approximately 5 degrees C and various aspects of their freeze-avoidance response were examined from early winter until early spring. Plasma levels of glycerol, trimethylamine oxide (TMAO) and urea were elevated by December 15 and continued to increase in fish held in ambient conditions. In contrast, fish held under warm conditions exhibited decreased glycerol and urea content in plasma, muscle and liver. Plasma and liver TMAO levels also decreased in these fish while muscle TMAO did not vary from the initial values. The activity of liver enzymes involved with the production of glycerol did not differ significantly between groups and had decreased by the end of the study. Antifreeze protein (AFP) expression increased over the duration of the experiment. In January samples, AFP activity (thermal hysteresis) did not vary significantly between groups but mRNA levels were significantly lower in the smelt held at warm temperatures. (+info)
Glycerol production in rainbow smelt (Osmerus mordax) may be triggered by low temperature alone and is associated with the activation of glycerol-3-phosphate dehydrogenase and glycerol-3-phosphatase.
Rainbow smelt (Osmerus mordax) accumulate high levels of glycerol in winter that serves as an antifreeze. Fish were subjected to controlled decreases in water temperature and levels of plasma glycerol, liver metabolites and liver enzymes were determined in order to identify control mechanisms for the initiation of glycerol synthesis. In two separate experiments, decreases in temperature from 8 degrees C to 0 degrees C over a period of 10-11 days resulted in increases in plasma glycerol from levels of less than 4 mmol l(-1) to approximate mean levels of 40 (first experiment) and 150 mmol l(-1) (second experiment). In a third experiment, decreases in temperature to -1 degrees C resulted in plasma glycerol levels approaching 500 mmol l(-1). The accumulation of glycerol could be driven in either December or March, thus eliminating decreasing photoperiod as a necessary cue for glycerol accumulation. Glycerol accumulation in plasma was associated with changes in metabolites in liver leading to increases in the mass action ratio across the reactions catalyzed by glycerol-3-phosphate dehydrogenase (GPDH) and glycerol-3-phosphatase (G3Pase). The maximal, in vitro activity of GPDH, increased twofold in association with a sharp increase in plasma glycerol level. The metabolite levels and enzyme activities provide complementary evidence that GPDH is a regulatory site in the low temperature triggered synthesis of glycerol. Indirect evidence, based on calculated rates of in vivo glycerol production by liver, suggests that G3Pase is a potential rate-limiting step. As well, transient increases in glyceraldehyde-3-phosphate dehydrogenase and alanine aminotransferase suggest that these sites are components of a suite of responses, in rainbow smelt liver, induced by low temperature. (+info)
Nucleotide diversity of Japanese isolates of infectious hematopoietic necrosis virus (IHNV) based on the glycoprotein gene.
Infectious hematopoietic necrosis virus (IHNV), a member of the genus Novirhabdovirus, causes a highly lethal disease of salmonid fish. In the present study, G gene nucleotide sequences of 9 Japanese IHNV isolates obtained from 1971 to 1996 were analyzed to evaluate the genetic diversity and compared with IHNV isolates from North America and Europe. A radial phylogenetic tree revealed 5 major clusters including 3 genogroups (U, M and L) for North American isolates and 1 genogroup for European isolates. Five Japanese isolates from 1971 to 1982 appeared in the cluster for genogroup U, while the remaining Japanese isolates from 1980 to 1996 formed a new genogroup, JRt (Japanese rainbow trout). Maximum nucleotide diversity among the Japanese isolates was 4.5%, which was greater than that within the North American isolates (3.6%), and the degree of nucleotide diversity within Japanese isolates was increased by inclusion of the genogroup JRt isolates. It was concluded that Japanese isolates shared a common source with the genogroup U of the North American isolates and that there were large divergences between Japanese isolates before and after the 1980s. (+info)
The evolutionary history of sharp- and blunt-snouted lenok (Brachymystax lenok (Pallas, 1773)) and its implications for the paleo-hydrological history of Siberia.