Nongenetic variation, genetic-environmental interactions and altered gene expression. II. Disease, parasite and pollution effects

Effect of severe environmental thermal stress on redox state in salmon

Fish are exposed to many kinds of environmental stressors and the chances of succumbing to infectious diseases may be increased a result. For example, an acute increase in temperature can induce numerous physiological changes in the body. In the present study, we examined the redox state in response to a severe acute stress resulting from heat shock in teleost coho salmon (Oncorhynchus kisutch). The plasma lipid peroxides levels in fish gradually increased after heat shock treatment. By 2.5 h post-heat stress, plasma glutathione (GSH) levels had decreased, but they had returned to basal levels by 17.5 h post-stress. Plasma superoxide dismutase activities in stressed fish were significantly increased compared with those in control fish at 17.5 h post-stress, but had returned to basal levels by 48 h post-stress. Expression levels of hepatic GSH and heat shock protein 70 gradually increased after heat shock treatment. These results concerning the changing patterns of multiple important redox-related biomarkers suggest that severe thermal stressors can affect the redox state and induce oxidative stress in ectothermal animals, such as fish, in vivo. Hence, manipulation of appropriate thermal treatment may possibly be useful to control fish fitness.

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The plasma lipid peroxides levels gradually increased after heat shock.

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The plasma glutathione levels had decreased, but they had returned to basal levels.

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The plasma superoxide dismutase activities were increased.

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The hepatic glutathione and heat shock protein 70 levels gradually increased.

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Severe thermal stressors can affect the redox state and might induce oxidative stress.

Acetylcholinesterase activity in the host-parasite system of the cod Gadus morhua and acanthocephalan Echinorhynchus gadi from the southern Baltic Sea

Acetylcholinesterase (AChE) activity measurement is widely used as a specific biomarker of neurotoxic effects. The aim of this study was to evaluate AChE activity in a host fish (the cod) and its acanthocephalan parasite Echinorhynchus gadi from the southern Baltic. AChE activity in hosts and parasites was inversely related: the highest cod AChE activity corresponded to the lowest E. gadi enzymatic activity and vice versa ("mirror effect"). This is the first report on the simultaneous application of this biomarker in cod and its acanthocephalan parasites. Results obtained for the host-parasite system are complementary and provide comprehensive information about the response of this biomarker. Analysis of the system allows for detection of a greater number of factors influencing AChE activity in the marine environment than separate analysis of the host and parasites. Thus, AChE activity measurement in a host-parasite system may be considered to be a promising tool for biomonitoring.

Insights into the mechanisms of copper tolerance of a population of black-banded rainbowfish (Melanotaenia nigrans) (Richardson) exposed to mine leachate, using 64/67Cu

This study investigates the mechanisms of copper tolerance of a population of black-banded rainbowfish (Melanotaenia nigrans) (Richardson). The population has been exposed to elevated copper concentrations for over 40 years, due to leachate from the Rum Jungle uranium/copper mine. At the time of collection the 96 h EC(50) of exposed [E] fish was 8.3 times higher than that of reference [R] fish. The bioconcentration of 64/67Cu in fish was used to investigate the mechanism of copper tolerance in E fish. Both E and R fish were exposed to low (L(Cu), 30 microg Cu l(-1)) and elevated (E(Cu), 300 microg Cu l(-1)) copper concentrations for 24 and 48 h, respectively. Radioactivity was measured at seven or eight time points in four tissue sections: head (including gills, heart and brain), internal organs (including gastrointestinal tract, liver, kidneys and gonads), muscle and whole body. One-compartment bioconcentration models were fit to data and compared using an F-test. Copper concentrations in all tissue sections were significantly (P<0.05) less (up to 50%) in E fish compared with the respective tissue sections of R fish when exposed to both L(Cu) and E(Cu). The exception was copper accumulation in the internal organs, which was not significantly different between E and R fish exposed to E(Cu). The mechanism of copper tolerance was concluded to be reduced copper uptake in the gills, rather than increased binding or elimination. Allozyme electrophoresis was performed to determine if genetic selection had occurred in the E fish population. Allozyme frequencies at the AAT-1 and GPI-1 loci were significantly (P<0.05) different between E and R fish. Heterozygosity was reduced in E fish compared with that of R fish. Collectively these results suggest that genetic selection may have occurred in the E fish population. Consequently, the selection of allozymes less sensitive to copper may be another mechanism of copper tolerance of E fish. This is the first study on the mechanisms of copper tolerance in a wild fish population that has been exposed to elevated copper concentrations. These findings aid the understanding of metal tolerance in fish and emphasise the importance of sample selection and its implication for toxicity testing.

Genetic variation in Avicennia marina in three estuaries of Sydney (Australia) and implications for rehabilitation and management

In order to ensure conservation of mangroves, genetic diversity in remaining populations must be explored. Both morphological and isozyme analyses were used and compared in investigating the intra- and inter-estuarine variation in Avicennia marina in Sydney, the most urbanised area in Australia. Sediment characteristics, metal levels, tree attributes, leaf morphology and isozyme/allozyme analyses were conducted. Tree characteristics did not prove to be adequate genetic markers, but leaf morphology may be of use in this species. Isozyme/allozyme analyses indicated that genetic distance corresponded with geographic distance, although habitat metal levels may indicate local selection pressures. High levels of heterozygote deficiencies were displayed in each estuary, which could threaten future viability. The results hold implications for management as periodic isozyme analysis may be useful in indicating management needs. The identification of metal-tolerant types may also be useful. Transplantation among estuaries may assist in increasing genetic diversity, if considered desirable. Whatever the management aims, isozyme/allozyme analyses are shown to be useful for revealing genetic diversity in this species.

Nongenetic variation, genetic-environmental interactions and altered gene expression. III. Posttranslational modifications

The use of protein electrophoretic data for determining the relationships among species or populations is widespread and generally accepted. However, posttranslational modifications have been discovered in many of the commonly analyzed proteins and enzymes. Posttranslational modifications often alter the electrophoretic mobility of the modified enzyme or protein. Because posttranslational modifications may affect only a fraction of the total enzyme or protein, an additional staining band often appears on gels as a result, and this may confound interpretations. Deamidation, acteylation, proteolytic modification, and oxidation of sulfhydryl groups are modifications that often result in an electrophoretic mobility shift. Sialic acid-induced heterogeneity has been documented for many enzymes, but neuraminidase treatment can often remove sialic acids and produce gel patterns that are easier to interpret. In some cases, ontogenetic and tissue-specific expression may be due to posttranslational modifications rather than gene control and restricted expression, respectively. Methods of preventing, detecting and eliminating posttranslational modifications are discussed. Some posttranslational modifications may be useful for detecting cryptic genetic polymorphisms.

Nongenetic variation, genetic-environmental interactions and altered gene expression. I. Temperature, photoperiod, diet, pH and sex-related effects

The use of protein electrophoretic data for determining the relationships among species or populations is widespread and generally accepted. However, many confounding factors may alter the results of an electrophoretic study in such a way as to allow erroneous conclusions to be drawn in taxonomic, systematic or population studies. Such variables as temperature, photoperiod, salinity, pH and diet have been shown to influence enzymes and proteins both quantitatively and qualitatively. Production of distinct "cold" and "warm" isozymes or "seasonal" isozymes have been found in a variety of organisms. The factors that are or may be responsible for the appearance of these isozymes is discussed. Most studies that have demonstrated some apparent form of environmentally induced genetic expression have not determined that mechanisms responsible. However, proteolytic modification has been shown to produce seasonal isozymes of fructose 1,6-bisphosphatase in rabbit liver and may account for other seasonal isozymes. Acclimating organisms to various conditions may actually allow detection of cryptic genetic variation and provide valuable data. There are many aspects to consider in designing acclimation experiments, and the conditions used will vary according to the aim of the research. Polyploidy may contribute to the genesis of environmentally regulated isozymes. A review of this literature follows with additional hypotheses and conclusions. Recommendations are given for the resolution of real and potential problems.