Anaerobic metabolism in sublittoral living Mytilus galloprovincialis in the mediterranean—IV. Role of amino acids in adaptation to low salinities during anaerobiosis and aerobiosis

Genotoxic potential and heart rate disorders in the Mediterranean mussel Mytilus galloprovincialis exposed to Superdispersant-25 and dispersed diesel oil

The effects of ex situ exposure of Mytilus galloprovincialis to Superdispersant-25 (S-25), diesel oil and dispersed diesel oil mixtures were studied by the impact on level of DNA damage in haemocytes (comet assay) and the cardiac activity patterns of mussels. Specimens were exposed for 72 h in a static system to diesel oil (100 μL/L and 1 mL/L), S-25 (5 and 50 μL/L), and dispersed diesel oil mixtures M1 (diesel oil 100 μL/L + S-25 5 μL/L) and M2 (diesel oil 1 mL/L + S-25 50 μL/L). For positive control 40 μM CdCl2 was used. The comet assay results indicated genotoxic potential of S-25 while the effects of diesel oil alone were not observed. The highest response was detected for M1 while the effects of M2 were not detected. The heart rate disorders were recorded for the diesel oil (1 mL/L), S-25 (50 μL/L) and both dispersed diesel oil mixtures.

Non-native marine invertebrates are more tolerant towards environmental stress than taxonomically related native species: results from a globally replicated study

To predict the risk associated with future introductions, ecologists seek to identify traits that determine the invasiveness of species. Among numerous designated characteristics, tolerance towards environmental stress is one of the most favored. However, there is little empirical support for the assumption that non-native species generally cope better with temporarily unfavorable conditions than native species. To test this concept, we ran five pairwise comparisons between native and non-native marine invertebrates at temperate, subtropical, and tropical sites. We included (natives named first) six bivalves: Brachidontes exustus and Perna viridis, P. perna and Isognomon bicolor, Saccostrea glomerata and Crassostrea gigas, two ascidians: Diplosoma listerianum and Didemnum vexillum as well as two crustaceans: Gammarus zaddachi and G. tigrinus. We simulated acute fluctuations in salinity, oxygen concentration, and temperature, while we measured respiration and survival rates. Under stressful conditions, non-native species consistently showed less pronounced deviations from their normal respiratory performance than their native counterparts. We suggest that this indicates that they have a wider tolerance range. Furthermore, they also revealed higher survival rates under stress. Thus, stress tolerance seems to be a property of successful invaders and could therefore be a useful criterion for screening profiles and risk assessment protocols.

Seasonal variability of free amino acids in two marine bivalves, Macoma balthica and Mytilus spp., in relation to environmental and physiological factors

The seasonal variability of the intracellular free amino acid (FAA) concentration was studied in 5 Macoma balthica populations and 7 Mytilus spp. populations along their European distribution. Because of the well known physiological role of FAA as organic osmolytes for salinity induced cell volume regulation in marine osmoconformers, FAA variations were compared in bivalve populations that were exposed to high vs. low intraannual salinity fluctuations. In general, seasonal FAA variations were more pronounced in M. balthica than in Mytilus spp. In both bivalve taxa from different locations in the Baltic Sea, highest FAA concentrations were found in autumn and winter and low FAA concentrations were measured in summer. Seasonal patterns were less pronounced in both taxa at locations with constant salinity conditions. In contrast to Baltic Sea populations, Atlantic and Mediterranean bivalves showed high FAA concentrations in summer and low values in winter, regardless of seasonal salinity fluctuations. Significant seasonal FAA variations at locations with constant salinity conditions showed that salinity appeared not to be the main factor in determining FAA concentrations. The seasonal patterns of the main FAA pool components, i.e. alanine, glycine and taurine, are discussed in the context of seasonal variations in environmental factors (salinity, temperature) and physiological state (glycogen content, reproductive stage).

Free amino acid composition in juveniles of Mytilus galloprovincialis: Spatial variability after Prestige oil spill

Composition of free amino acids (FAA) in juveniles of Mytilus galloprovincialis was analysed along a large geographical coastline area in Galicia (NW Spain). Individuals were sampled in February 2003, three months after the Prestige oil spill. Pollution values at sampling time were reported as polycyclic aromatic hydrocarbons (PAHs) concentrations in soft tissues of individuals and varied between the highest amount observed in Carrumeiro mussels (502 ng/g dw) and the lowest in Pindo mussels (196 ng/g dw), both locations being close to each other in the centre of the geographical area under study. Pollution values in the other populations varied within the range of 241-347 ng/g dw. Total free amino acids (TFAA) were highest in Aguiño-Pindo-Carrumeiro juveniles at the centre of the Coastline area studied (420-462 micromol/g dw) as compared to the other populations at North and South of Galicia (312-347 micromol/g dw). TFAA results were based on the variability observed in protein free amino acids (PFAA micromol/g dw) among populations (214-249 micromol/g dw for Aguiño-Pindo-Carrumeiro mussels and 98-149 micromol/g dw for the other populations) whereas non-protein free amino acids (NPFAA) taurine and ornithine did not show any significant spatial pattern of variation. Glycine and alanine represented the most abundant PFAA (16-29% and 2.7-11.9% of TPFAA, respectively) and significant correlations between PFAA and both the protein content of soft tissues (r=-0.82) and the condition index of juveniles (r=0.86) were observed. No significant relationships were detected, however, between pollution values in soft tissues as PAHs and FAA profiles with the exception of alanine concentrations as percentage of TFAA (r=0.88; P<0.01). The latter seemed to be an "all or nothing" effect likely due to the influence of other abiotic factors at one of the sampling sites. Such relationship was found not significant when the outlier represented by Carrumeiro mussels was removed from the analysis. The most abundant free amino acid taurine (43.2-68.5%TFAA) followed an inverse variability of that of glycine and by extension of the group PFAA most likely as a compensatory decrease in mussel populations with low protein content (and high condition index). Accordingly, taurine:glycine (t:g) ratio varied between 1 and 2 in most mussel populations but increased up to 3.2-4.2 in Miranda and Bueu mussels at both ends of the geographical interval studied with a corresponding PAHs concentrations of 261 and 304 ng/g dw, respectively. These mussel populations with the highest t:g ratios were characterised by the lowest PFAA contents (below 40%) and condition index values (below 10%). Results of the present study established a significant link between energetic status of growing juveniles and FAA concentrations in environments with different pollution degrees. Variability of the free amino acids profiles in soft tissues were related to endogenous factors of juveniles (protein content, condition index) whereas no relationship with contamination values could be observed. The utility of t:g ratio as general condition factor for M. galloprovincialis is also corroborated for in situ growing juveniles.

Following the heart: temperature and salinity effects on heart rate in native and invasive species of blue mussels (genusMytilus)

The three species of blue mussels, Mytilus trossulus Gould 1850, M. edulis Linnaeus 1758 and M. galloprovincialis Lamarck 1819, have distinct global distribution patterns that are hypothesized to reflect differences in their tolerances of temperature and salinity. We examined effects on heart rate (beats min–1) of acute exposure and acclimation to different combinations of temperature and salinity to test this hypothesis and, in the context of the invasive success of M. galloprovincialis, to gain insights into the factors that may explain the replacement of the temperate Pacific native, M. trossulus, by this Mediterranean Sea invader along much of the California coast. Heart rate of M. trossulus was significantly higher than that of M. galloprovincialis, consistent with evolutionary adaptation to a lower habitat temperature (temperature compensation) in the former species. Heart rates of M. trossulus/M. galloprovincialis hybrids were intermediate between those of the parental species. Following acclimation to 14°C and 21°C, heart rates of all species exhibited partial compensation to temperature.

Heart rate increased with rising temperature until a high temperature was reached at which point activity fell sharply, the high critical temperature(Hcrit). Hcrit increased with increasing acclimation temperature and differed among species in a pattern that reflected their probable evolutionary adaptation temperatures: M. galloprovincialis is more heat tolerant than the other two congeners. Ability to sustain heart function in the cold also reflected evolutionary history: M. trossulus is more cold tolerant than M. galloprovincialis.

Heart rates for all three congeners decreased gradually in response to acute reductions in salinity until a low salinity (Scrit)was reached at which heart rate dropped precipitously. Scrit decreased with decreasing salinity of acclimation and was generally lowest for M. galloprovincialis. Mortality during acclimation under common garden conditions was greatest in M. trossulus and was highest at high acclimation temperatures and salinities. These intrinsic differences in basal heart rate, thermal and salinity responses, acclimatory capacity, and survivorship are discussed in the contexts of the species' biogeographic patterning and, for the invasive species M. galloprovincialis, the potential for further range expansion along the Pacific coast of North America.

Effects of a New Isoquinolinone Derivative on Induction of Action Potential Bursts in Central Snail Neuron

The effects of 7-bromo-1,4-dihydro-2-phenyl-4,4-bis(4-pyridinylmethyl)2H-isoquinolin-3-one dihydrochloride (BDPBI) on induction of action potential bursts were studied pharmacologically on the RP4 central neuron of the giant African snail (Achatina fulica Ferussac). The effects of m-3M3FBS, a phospholipase activator and HTMT, a histamine (H1) receptor agonist, on the neuron were also tested. The RP4 neuron showed spontaneous firing of action potential. Extracellular application of BDPBI (150 micromol/l) reversibly elicited bursts of potential (BoP) on the neuron. m-3M3FBS and HTMT also elicited BoP on the RP4 neuron. The BoP elicited by BDPBI were blocked by U73122 (6 micromol/l), a compound commonly used as a phospholipase C (PLC) inhibitor. Neomycin (3.5 mmol/l), a high-magnesium solution (30 mmol/l), replacing the physiological sodium ion with lithium ion or adding diphenhydramine, chloropheniramine decreased the BoP elicited by BDPBI. The BoP elicited by BDPBI were not inhibited after administration with (1) prazosin, propranolol, atropine, d-tubocurarine, hexamethonium, haloperidol, cimetidine, (2) calcium-free solution, (3) high-potassium (12 mmol/l) solution, and (4) pretreatment with KT-5720. The BoP elicited by HTMT was not inhibited after administration of diphenhydramine or chloropheniramine. Voltage-clamped studies revealed that BDPBI decreased the amplitudes of calcium and steady-state outward currents while it did not alter the amplitude of the fast inward current. No negative slope relationship of the steady-state current voltage relationship was found in BDPBI-treated neurons. It is concluded that BDPBI reversibly elicited BoP in the central snail neuron. The effect was not due to (1) the extracellular calcium ion fluxes, or (2) the activation of cholinergic, adrenergic or histamine receptors. The BDPBI-elicited BoP were dependent on the phospholipase activity in the neuron.

Biosynthesis and role in osmoregulation of glycine-betaine in the Mediterranean mussel Mytilus galloprovincialis LMK

Quaternary bases, for example glycine-betaine, are difficult to quantify in biological materials because of a lack of specificity. However, nuclear magnetic resonance (NMR) can determine quaternary bases even in the presence of high water concentrations. Using NMR concentrations of glycine-betaine, the posterior adductor muscle of the Mediterranean mussel Mytilus galloprovincialis were measured up to 256 micromole/g dry weight. These concentrations were related to external salinity concentrations. The biosynthesis of glycine-betaine was demonstrated in M. galloprovincialis from the precursor (14)C choline.