Metabolism and growth of juveniles of Litopenaeus vannamei: effect of salinity and dietary carbohydrate levels

The present study was designed to understand how carbohydrate (CBH) and protein metabolism are related in the penaeid shrimp Litopenaeus vannamei. With this information, we obtained a comprehensive schedule of the protein-carbohydrate metabolism including enzymatic, energetic, and functional aspects. We used salinity to determine its role as a modulator of the protein-carbohydrate metabolism in shrimp. Two experiments were designed. The first experiment evaluated the effect of CBH-salinity combinations in growth and survival, and hemolymph glucose, protein, and ammonia levels, digestive gland glycogen, osmotic pressure, and glutamate dehydrogenase (GDH) of L. vannamei juveniles acclimated during 18 days at a salinity of 15 per thousand and 40 per thousand. The second experiment was done to evaluate the effect of dietary CBH level on pre- and postprandial oxygen consumption, ammonia excretion, and the oxygen-nitrogen ratio (O/N) of juvenile L. vannamei in shrimps acclimated at 40 per thousand salinity. We also evaluated the ability of shrimp to carbohydrate adaptation. We made phosphoenolpyruvate carboxykinase (PECPK) and hexokinase activity measurements after a change in dietary carbohydrate levels at different times during 10 days. The growth rate depended on the combination salinity-dietary CBH-protein level. The maximum growth rate was obtained in shrimps maintained at 15 per thousand salinity and with a diet containing low CBH and high protein. The protein in hemolymph is related to the dietary protein levels; high dietary protein levels produced a high protein concentration in hemolymph. This suggests hemolymph is able to store proteins after a salinity acclimation. Depending on the salinity, the hemolymph proteins could be used as a source of osmotic effectors or as metabolic energy. The O/N values obtained show that shrimp used proteins as a source of energy, mainly when shrimps were fed with low CBH. The role played by postprandial nitrogen excretion (PPNE) in apparent heat increase (AHI) (PPNE/AHI ratio) is lower in shrimps fed diets containing high CBH in comparison with shrimps fed diets containing low CBH levels. These results confirm that the metabolism of L. vannamei juveniles is controlled by dietary protein levels, affecting the processes involved in the mechanical and biochemical transformations of ingested food. A growth depression effect was observed in shrimps fed with low-CBH protein diets and maintained in 40 per thousand salinity. In these shrimps, the hemolymph ammonia concentration (HAC) was significantly higher than that observed in shrimps fed with low CBH and maintained in 15 per thousand salinity. That high HAC level coincided with lower growth rate, which suggests that this level might be toxic for juveniles of L. vannamei. Results obtained for GDH activity showed this enzyme regulated both HAC and hemolymph protein levels, with high values in shrimps fed with low CBH levels and maintained in 40 per thousand salinity, and lower in shrimps fed with high CBH and maintained in 15 per thousand salinity. These differences mean that shrimp with a high-gill GDH activity might waste more energy in oxidation of the excess proteins and amino acids, reducing the energy for growth. It was evident that L. vannamei can convert protein to glycogen by a gluconeogenic pathway, which permitted shrimp to maintain a minimum circulating glucose of 0.34 mg/ml in hemolymph. A high PECPK activity was observed in shrimps fed a diet containing low CBH level indicating that the gluconeogenic pathway is activated, as in vertebrates by low dietary CBH levels. After a change in diet, we observed a change in PEPCK; however, it was lower and seems to depend on the way of adaptation, because it occurred after 6 days when adapting to a high-CBH diet and with little change for the low-CBH diet.     

Salinity effects on viability, metabolic activity and proliferation of three Perkinsus species

Little is known regarding the range of conditions in which many Perkinsus species may proliferate, making it difficult to predict conditions favorable for their expansion, to identify conditions inducing mortality, or to identify instances of potential cross-infectivity among sympatric host species. In this study, the effects of salinity on viability, metabolic activity and proliferation of P. marinus, P. olseni and P. chesapeaki were determined. Specifically, this research examined the effects of 5 salinities (7, 11, 15, 25, 35 per thousand), (1) without acclimation, on the viability and metabolic activity of 2 isolates of each Perkinsus species, and (2) with acclimation, on the viability, metabolic activity, size and number of 1 isolate of each species. P. chesapeaki showed the widest range of salinity tolerance of the 3 species, with high viability and cell proliferation at all salinities tested. Although P. chesapeaki originated from low salinity areas (i.e. <15 per thousand), several measures (i.e. cell number and metabolic activity) indicated that higher salinities (15, 25 per thousand) were more favorable for its growth. P. olseni, originating from high salinity areas, had better viability and proliferation at the higher salinities (15, 25, 35 per thousand). Distinct differences in acute salinity response of the 2 P. olseni isolates at lower salinities (7, 11 per thousand), however, suggest the need for a more expansive comparison of isolates to better define the lower salinity tolerance. Lastly, P. marinus was more tolerant of the lower salinities (7 and 11 per thousand) than P. olseni, but exhibited reduced viability at 7 per thousand, even after acclimation.     

Interactive effects of diet and temperature on the scope for growth of the scallop Argopecten purpuratus during reproductive conditioning

Mature individuals of Argopecten purpuratus from suspended culture in Tongoy Bay, northern Chile were conditioned at two temperatures (16 and 20 degrees C) and three different diets (mixture of pure microalgae, microalgae supplemented with lipids and microalgae supplemented with carbohydrates). The food, equivalent to 3% daily of the animal dry weight was supplied continuously by a peristaltic pump. The rates of different physiological processes were measured on 18 scallops (three replicates per temperature/diet combination) during the third week of conditioning. Nine scallops came from the group conditioned at 16 degrees C and other nine from the group conditioned at 20 degrees C (each scallop from a different tank). As in the conditioning experiment, physiological measurements were made in controlled temperature rooms using the same experimental diets. Argopecten purpuratus did not show significant differences in clearance rate between 16 and 20 degrees C when fed with pure microalgae and microalgae+lipids, showing a well known capability of bivalves to acclimate their physiological rates within a certain range of temperature. On the other hand a clear effect of the composition of the diet on the clearance rate was observed. When microalgae were supplemented with a lipid emulsion, clearance rate was highly stimulated, showing values significantly higher in comparison with either pure microalgae, or a mixed diet of microalgae+carbohydrate. These highest feeding rates can be related with the presence of essential fatty acids in the diet, which are considered as very important compounds during the gametogenesis of invertebrates as well as during the development of ova into normal larvae. Thus A. purpuratus can actively regulate clearance rate and does not simply switch between feeding and non-feeding states. The data also suggest the presence of chemical receptors at the level of the gills and/or labial palps, which seem able to detect specific nutritive compounds present in the diet. Absorption efficiency was independent of temperature and was higher with pure microalgae and with microalgae+lipids. The lowest efficiencies were recorded with the diet supplemented with carbohydrates. The energy expended in oxygen uptake and ammonia excretion was very similar in the different experimental diets and temperatures. Scope for growth in A. purpuratus appears mainly affected by the diet and not by temperature. While the lower SFG seems to be associated with diets composed of pure microalgae and microalgae+carbohydrates, the highest values being found for a diet rich in lipids. The data were in agreement with the reproductive conditioning of A. purpuratus, where the highest percentage of ripe scallops occurred in individuals fed with a diet of microalgae supplemented with lipids at both temperatures. Similarly the highest larval survival rate was obtained from gametes released by scallops conditioned with the diet containing lipids.     

Digestive plasticity and the cost of acclimation to dietary chemistry in the omnivorous leaf-eared mouse Phyllotis darwini

We examined the costs associated with acclimation in an omnivorous mouse (Phyllotis darwini) fed two contrasting diets (carbohydrate-rich and protein-rich). We studied the response of gut morphology and digestive performance in animals shifted to a novel diet at different developmental stages. When acclimated adult animals were shifted to the alternative diet, energy digestibility decreased. We also found long-term consequences to diet acclimation. Animals reacclimated for 15 days to an alternative diet did not increase digestive performance. Although no effects of diet on gut morphology were noted, a significant positive correlation between energy digestibility and small intestinal length was found, explaining most of the variability observed in energy digestibility. These results suggest that caution should be used when defining adaptive changes if the possible cost of acclimation is neglected. Accepted: 18 May 2000     

Effects of long-term exposure to different salinities on the location and activity of Na+-K+-ATPase in the gills of juvenile mitten crab, Eriocheir sinensis

The euryhalinity of mitten crab, Eriocheir sinensis, is based on osmoregulation, and thus on the activity of Na(+)-K(+)-ATPase. We studied location and activity of this enzyme in gills of juvenile crabs exposed to 5 per thousand, 25 per thousand, and 40 per thousand salinity. The posterior gills showed always a high number of immunopositive cells (IPC), staining with fluorescent antibody against Na(+)-K(+)-ATPase, covering at 5 per thousand the entire lamellae. At 25 per thousand, they showed fewer IPC which occurred only at the bases of the lamellae. Enzyme activity was consistently higher in posterior than in anterior gills. Low salinity stimulated the activity only in posterior gills. Both histochemical and enzymatic results are consistent with previous ultrastructural observations showing that the epithelial cells of the posterior, but not the anterior gills exhibit typical traits of ionocytes. While an increase in Na(+)-K(+)-ATPase activity at a reduced salinity is consistent with a strong hyper-osmoregulatory capacity in juvenile crabs, a low activity at an enhanced salinity suggests a physiological response, directed towards a reduction of Na(+) uptake. The activity increase of ion-transporting enzymes is directly related to spatial changes in their distribution along the osmoregulatory tissue, i.e. an enhanced number of IPC scattered along the entire lamellae. In juveniles, this allows for successful development and growth at reduced salinities.     

Responses of winkles digestive cells and their lysosomal system to environmental salinity changes

After acclimation to 100, 75 and 50% of Sea Water (SW) external salinities, a significant reduction in MET (Mean Epithelial Thickness) and MDR (Mean Diverticular Radius) indicates a decrease in the digestive cell volume dependant on the lowering of environmental salinity. The interstitial connective tissue seems to be unable to osmoregulate and hence stand severe changes in cell size depending on external salinity. 50% SW acclimated periwinkles show a general pattern of general stress response (decreasing MET and MDR, and increasing ND -Numerical Density of lysosomes- and lysosomal size). A reduction in number and size of digestive lysosomes in winkles acclimated to 75% of Sea Water evidences the functioning of regulatory mechanism of digestive cell volume.     

Acute and acclimated digestive responses of the cockle Cerastoderma edule (L.) to changes in the food quality and quantity. II. Enzymatic, cellular and tissular responses of the digestive gland

Cockles Cerastoderma edule were fed two different concentrations of two diets with different qualities which were achieved by mixing different proportions of ashed silt particles with cells of the microalgae Tetraselmis suecica. After 3 days (acute response) and 11 days (acclimated response) of exposure to the diets, we analysed the digestive activity of the digestive gland using cyto-histological and enzymatic techniques. We measured (i) the volumetric fraction of digestive and basophilic cells in digestive tubules, (ii) the diverticular radius and the thickness of digestive epithelia, (iii) the stereological parameters characterizing the lysosomal system and, (iv) dry weight, soluble protein content and specific and total amylase, cellulase, laminarinase, and protease activities of the digestive gland. In the conditions of the present study, specific cellulase and laminarinase activities in the digestive gland of cockles were correlated with the volumetric fraction of basophilic cells (r=0.672 and 0.642, respectively), whereas the specific protease was highly correlated (r=0.866) with lysosomal volume density. The implications of these correlations are discussed in relation to the feeding and absorptive parameters reported in the preceding publication. In the acute response, adjustments of the synthesis of constituents of the lysosomal/proteolytic system of the digestive cells seemed to be the only mechanism operating at the digestive level to respond to the changes in food availability. Lysosomal volume density increased with rising ingestion rate of organic matter, however, the occurrence of a limit in this short-term tissular response would account for the recorded trade-off between absorption efficiency and ingestion rate with different food qualities. With regard to acclimation, food quality determined the nature of the response of the digestive gland. With low quality diets, a time-dependent capability of the digestive gland for intensifying lysosomal/proteolytic production explains the increase of food absorption rates that result from higher filtration and ingestion rates. With high quality food, digestive acclimation differed with food particle concentration: with low rations, in spite of constant morphometrical and stereological parameters, the significant changes in the absorptive balance of biochemical components suggests the existence of an increased production of lysosomes that promotes an accelerated turn-over rate of the digestive epithelia. With high food concentrations, this response was coupled with increased activities of cellulase and laminarinase enzymes, probably as a consequence of higher rates of enzyme secretions from basophilic cells.     

The effects of rapid salinity change on in vivo arginine kinase flux in the juvenile blue crab,Callinectes sapidus

The effect of acclimation salinity and salinity changes on the concentration of high-energy phosphate metabolites and arginine kinase (AK) flux was examined in vivo in juvenile blue crabs using 31P-nuclear magnetic resonance (NMR). Crabs were acclimated for 7 days to a salinity of 5 or 35 per thousand and then placed in a flow apparatus that could sustain the animals while NMR spectra were acquired. Crabs were subjected to either hyperosmotic salinity changes, where an animal acclimated to 5 per thousand was exposed to a salinity of 35 per thousand, or hyposmotic changes, which involved the reciprocal exchange. Neither acclimation salinity nor salinity change had a significant effect on the concentrations of arginine phosphate, inorganic phosphate or ATP. 31P-NMR saturation transfer experiments were used to determine the effect of salinity on the forward and reverse flux of the AK reaction. There was no significant effect of acclimation salinity or salinity change on the flux rate through this reaction. This is in contrast to previous results, which showed that AK flux in isolated muscle was sensitive to prevailing osmotic conditions (Holt and Kinsey, J. Exp. Biol. 205 (2002) 1775-1785). The present study indicates that the integrated osmoregulatory capacity of the intact animal is sufficient to preserve cellular energy status and enzyme function during acute salinity changes.     

Effects of reduced salinity on survival, growth, reproductive success, and energetics of the euryhaline polychaete Capitella sp. I

Physiological adjustment to water of reduced salinity requires energy expenditure. In this study we sought to determine the fitness costs associated with such adjustment in the euryhaline polychaete Capitella sp. I, and the extent to which such costs could be explained by increased rates of energy expenditure. In a series of experiments conducted at 20 degrees C, salinity was reduced from 30 per thousand to either 25, 20, 15, 12, or 10 per thousand within 72 h after the larvae had been induced to metamorphose. Juveniles were reared on fine, organic-rich sediment. Over the next 15-30 days, we determined survival, growth, fecundity, and rates of respiration and feeding (via fecal pellet production). Larval salinity tolerance was also determined. Juvenile survival at salinities as low as 12-15 per thousand was comparable to that at 30 per thousand. The lower limit of salinity tolerance was 10-12 per thousand at 20 degrees C for both larvae and juveniles. Juveniles grew significantly more slowly at 12-15 per thousand in six of the seven experiments. Fecundity, however, was generally highest at intermediate salinities of 20-25 per thousand, and comparable at 30 and 15 per thousand. No individuals released embryos at 12 per thousand over the approximately 30-day observation periods in any of the three experiments in which the worms were reared at this low salinity. Reduced growth rates were not explained by differences in rates of respiration at different salinities: at reduced salinity, respiration rates were either statistically equivalent to (P>0.10) or significantly below (P<0.05) those recorded for animals maintained at 30 per thousand. Lower growth rates at lower salinities were best explained by reduced feeding rates. Further studies are required to determine whether digestive efficiency, growth hormone concentrations, or reproductive hormone concentrations are also altered by low salinity in this species.     

Branchial osmoregulatory response to salinity in the gilthead sea bream, Sparus auratus

The branchial osmoregulatory response of gilthead sea bream (Sparus auratus L.) to short-term (2-192 hr) and long-term (2 weeks) exposure to different environmental salinities (5 per thousand, 15 per thousand, 25 per thousand, 38 per thousand and 60 per thousand) was investigated. A "U-shaped" relationship was observed between environmental salinity and gill Na+,K+ -ATPase activity in both long- and short-term exposure to altered salinity, with the increase in activity occurring between 24 and 96 hr after the onset of exposure. Plasma osmolality and plasma ions (sodium, chloride, calcium and potassium) showed a tendency to increase in parallel with salinity. These variables only differed significantly (P<0.05) in fish adapted to 60 per thousand salinity with respect to fish adapted to full-strength sea-water (SW). Plasma glucose remained unchanged whereas plasma lactate was elevated at 5 per thousand and 60 per thousand. Muscle water content (MWC) was significantly lower in fish adapted to 60 per thousand. Chloride cells (CC) were only present on the surface of the gill filaments and absent from the secondary lamellae. CC distribution was not altered by external salinity. However, the number and size of CC were significantly increased at salinity extremes (5 per thousand and 60 per thousand), whereas fish exposed to intermediate salinities (15 per thousand and 25 per thousand) had fewer and smaller cells. Furthermore, the CC of fish exposed to diluted SW became rounder whereas they were more elongated in fish in full-strength and hypersaline SW. This is consistent with previous reports indicating the existence of two CC types in euryhaline fish. At likely environmental salinities, gilthead sea bream show minor changes in plasma variables and the effective regulation of gill Na+,K+ -ATPase. However, at very low salinities both haemodilution and up-regulation of gill Na+,K+ -ATPase predict a poor adaptation most likely related to deficiency or absence of specific components of the CC important for ion xuptake.     

Lipids as energy source during salinity acclimation in the euryhaline crab Chasmagnathus granulata dana, 1851 (crustacea-grapsidae)

Lipids seem to be the major energy store in crustaceans. Moreover, they are extremely important in maintaining structural and physiological integrity of cellular and sub cellular membranes. During salinity adaptation, energy-demanding mechanisms for hemolymph osmotic and ionic regulation are activated. Thus, the main goal of this work was to verify the possible involvement of lipids as an energy source in the osmotic adaptation process. The estuarine crab Chasmagnathus granulata was captured and acclimated to salt water at 20 per thousand salinity and 20 +/- 2 degrees C, for 30 days. After acclimation, crabs were divided into groups of ten and transferred to fresh water (0 per thousand ), salt water at 40 per thousand salinity, or maintained in salt water at 20 per thousand salinity (control group), without feeding. Before and seven days after the salinity change, wet weight and lipid concentration in gills, muscle, hepatopancreas, and hemolymph were determined according to the colorimetric assay of sulphophosphovanilin. Results show that hepatopancreas lipids were not mobilized during osmotic stress regulation. Gill and muscle lipids were significantly lower in crabs subjected to hypo-osmotic stress than those subjected to the hyper-osmotic stress or maintained at the control salinity. Our results point to the occurrence of lipid mobilization and involvement of these compounds in the osmotic acclimation process in C. granulata, but with differences between tissues and the osmotic shock (hypo or hyper) considered.     

Ontogeny of osmoregulation in the crayfish Astacus leptodactylus

Osmoregulation was studied during the postembryonic development of Astacus leptodactylus Eschscholtz 1823 in juvenile stages 1-8 and in adults. Juveniles hatch and later stages develop in freshwater or in moderately saline waters. The time of acclimation from freshwater to a saline medium increased from early juveniles to adults. At all stages, it was longer than in comparable stages of marine crustaceans, reflecting the high impermeability of the teguments to water and ions. All stages were able to hyperisoosmoregulate. In freshwater, the ability to hyperosmoregulate was established at hatching and increased during development. The hemolymph osmolality increased from 286 mosm kg-1 in stage 1 juveniles to 419 mosm kg-1 in adults. All stages also hyperregulated at low salinities (7 per thousand and 13 per thousand salinity) and were osmoconformers at higher salinities up to 21 per thousand salinity. The lowest isosmotic salinity tended to increase with the developmental stages. The ability to osmoregulate at hatch and throughout postembryonic development is probably a key physiological adaptation in this and other freshwater crayfish.     

Are levels of digestive enzyme activity related to the natural diet in passerine birds?

Digestive capabilities, such as the rates nutrient hydrolysis and absorption, may affect energy intake and ultimately feeding behavior. In birds, a high diversity in gut biochemical capabilities seems to support the existence of a correlation between the morphology and physiology of the intestinal tract and chemical features of the natural diet. However, studies correlating the activity of digestive enzymes and the feeding habits at an evolutionary scale are scarce. We investigated the effect of dietary habits on the digestive physiological characteristics of eight species of passerine birds from Central Chile. The Order Passeriformes is a speciose group with a broad dietary spectrum that includes omnivorous, granivorous and insectivorous species. We measured the activity of three enzymes: maltase, sucrase and aminopeptidase-N. Using an autocorrelation analysis to remove the phylogenetic effect, we found that dietary habits had no effect on enzymatic activity. However, we found that granivorous and omnivorous species had higher levels of disaccharidase activities and insectivores had the lowest. The major difference in enzymatic activity found at the inter-specific level, compared to the reported lower magnitude of enzyme modulation owing to dietary acclimation, suggests that these differences to some extent have a genetic basis. However, the lack of a clear association between diet categories and gut physiology suggested us that dietary categorizations do not always reflect the chemical composition of the ingested food.     

Possible role of carbonic anhydrase, V-H(+)-ATPase, and Cl(-)/HCO3- exchanger in electrogenic ion transport across the gills of the euryhaline crab Chasmagnathus granulatus

We studied the participation of carbonic anhydrase (CA), V-H(+)-ATPase, and Cl(-)/HCO3- exchanger in electrogenic ion absorption through the gills of Chasmagnathus granulatus. CA activity was measured in anterior gills and posterior gills after acclimation to 2 per thousand, 10 per thousand, 30 per thousand (about seawater), and 45 per thousand salinity. The highest CA specific activity was detected in the microsomal fraction in anterior gills, and in the cytosolic fraction, in posterior ones. Both fractions were strongly induced by decreasing salinity only in posterior gills. Perfusion of posterior gills from crabs acclimated to either 2 per thousand or 10 per thousand with acetazolamide inhibited CA activity almost completely. In posterior gills from crabs acclimated to 2 per thousand and perfused with 20 per thousand saline (iso-osmotic for these crabs), acetazolamide reduced transepithelial potential difference (V(te)) by 47%, further addition of ouabain enhanced the effect to 88%. Acetazolamide had no effect in the same gills perfused with 30 per thousand saline (iso-osmotic for seawater acclimated crabs). Bafilomycin A1 and SITS (inhibitors of V-H(+)-ATPase and Cl(-)/HCO3-) reduced V(te) by 15-16% in gills perfused with normal 20 per thousand saline, and by 77% and 45%, respectively when they were applied in Na-free 20 per thousand saline, suggesting the participation of those transporters and cytosolic CA in electrogenic ion absorption.     

Aspects of the Cryobiology of the Intertidal Harpacticoid CopepodTigriopus brevicornis(O. F. Müller)

Cold-resistance studies of marine invertebrates have concentrated on intertidal sedentary organisms, which are often subjected to subzero air temperatures in winter. Mobile rock pool inhabitants have been rarely studied because such habitats are thought to buffer environmental variation. However, it is not uncommon for small upper-shore rock pools ( approximately 2 by 1 cm) to become completely frozen. Such supralittoral habitats are subject to extreme physicochemical fluctuations especially in salinity (0 to 300 per thousand) and temperature (-1 to +32degreesC) due to evaporation and dilution. The dominant invertebrate in such habitats is the harpacticoid copepod Tigriopus brevicornis. Aspects of the cryobiology of T. brevicornis were investigated using differential scanning calorimetry (DSC). Thermograms obtained from DSC allowed determinations of freeze-onset (supercooling point, SCP), melt-onset, and melt-peak (melting point, MP) temperatures, together with estimation of the proportion of water freezing in the samples. The effects of acclimation salinity, temperature, starvation, and reproductive state on these cryobiological parameters were investigated. Acclimation to increasing salinity depressed the SCP, with the highest salinity (70 per thousand) producing the lowest SCP, melt-onset, and MP temperatures at -27.5, -15.2, and -9.5degreesC respectively. The highest acclimation temperature (20degreesC) produced the lowest SCP (-23.4degreesC). Starvation significantly increased the SCP, melt-onset, and MP temperatures in comparison to fed individuals acclimated to the same salinity. The presence of eggs or ovaries in individual copepods elevated the SCP compared to nongravid females and males. LT50 studies showed that acclimation to high salinity improved the ability of T. brevicornis to survive in frozen seawater. Seventy parts per thousand acclimated individuals had an LT50 of 64.9 h compared with just 1.4 h for 5 per thousand acclimated individuals in frozen seawater at -5degreesC. The study shows that the cold-resistance capabilities of T. brevicornis can be affected by several different factors, and the link between the osmoconforming nature of this species and its cold resistance is discussed. Copyright 1997 Academic Press. Copyright 1997Academic Press     

Membrane-bound intestinal enzymes of passerine birds: dietary and phylogenetic correlates

Bird species exhibit great diversity in digestive tract morphology and enzymatic activity that is partly correlated with the chemical composition of their natural diets. However, no studies have assessed whether the activities of digestive enzymes of the enterocytes correlate with dietary chemical composition data analyzed as a continuous variable at an evolutionary scale. We used a phylogenetically explicit approach to examine the effect of diet on the hydrolytic activity of three digestive enzymes (maltase, sucrase, and aminopeptidase-N) in 16 species of songbirds (Order Passeriformes) from Central Chile. The total activities (μmol/min) of these enzymes were positively associated with body mass using both conventional least squares regressions and phylogenetically independent contrasts. After removing mass effects, we found a significant negative correlation between the ratio of aminopeptidase-N and maltase to the proportion of seeds found in the gizzard, but this relationship was no longer significant after controlling for phylogeny. When we analyzed the specific nutritional content of the diet, we found that the percentage of nitrogen in diet was negatively correlated with residual maltase activity and positively correlated with the ratio aminopeptidase-N/maltase. Given the large interspecific differences in biochemical capacity, we conclude that these differences reflect genetically determined evolutionary changes associated with the nutrient contents of each species’ natural diet.     

The response of digestive proteases to abrupt salinity decrease in the euryhaline sparid Sparus aurata L

The response of the digestive proteases to abrupt salinity change was studied in juvenile gilthead sea bream (Sparus aurata) for 15 days after transfer from 33 per thousand to 21 per thousand. Salinity decrease affected significantly neither the activity of total acid proteases in stomach, nor the activities of total alkaline proteases and major serine proteases--trypsin and chymotrypsin--in the alkaline part of the intestine. The activity of the major proteases was significantly different between the alkaline segments of the intestine, with the posterior intestine presenting the highest activities followed by the pyloric caeca. This distribution pattern remained unaffected by salinity decrease. Notably, salinity change led to significant alterations in elastase and carboxypeptidase activity. The changes were more prominent in the upper part of the intestine (pyloric caeca and anterior intestine) than in the posterior intestine. In pyloric caeca significant alteration of carboxypeptidase A and B activities was observed, elastase changes were confined to anterior intestine together with alterations in carboxypeptidase B activity, while in posterior intestine the changes were restricted to carboxypeptidase A activity. The results are discussed in relation to the osmoregulatory action of the intestinal segments and dietary protein digestion.     

Enzymatic digestive activity and absorption efficiency in Tagelus dombeii upon Alexandrium catenella exposure

We analyzed absorption efficiency (AE) and digestive enzyme activity (amylase, cellulase complex, and laminarinase) of the infaunal bivalve Tagelus dombeii originating from two geographic sites, Corral-Valdivia and Melinka-Aysén, which have different long-term paralytic shellfish poisoning (PSP) exposure rates. We report the effects of past feeding history (origin) on T. dombeii exposed to a mixed diet containing the toxic dinoflagellate Alexandrium catenella and another dinoflagellate-free control diet over a 12-day period in the laboratory. Absorption efficiency values of T. dombeii individuals that experienced PSP exposure in their habitat (Melinka-Aysén) remained unchanged during exposure to toxic food in the laboratory. In contrast, T. dombeii from a non-PSP exposure field site (Corral-Valdivia) showed a significant reduction in AE with toxic exposure time. This study established that the amylase and cellulase complexes were the most important enzymes in the digestive glands of Tagelus from both sites. The temporal evolution of enzymatic activity under toxic diet was fitted to exponential (amylase and cellulase) and to a logarithmic (laminarinase) models. In all fits, we found significant effect of origin in the model parameters. At the beginning of the experiment, higher enzymatic activity was observed for clams from Corral-Valdivia. The amylase activity decreased with time exposure for individuals from Corral and increased for individuals from Melinka. Cellulase activity did not vary over time for clams from Corral, but increased for individuals from Melinka and laminarinase activity decreased over time for individuals from Corral and remained unchanged over time for Melinka. A feeding history of exposure to the dinoflagellate A. catenella was reflected in the digestive responses of both T. dombeii populations.     

Salinity responses of benthic microbial communities in a solar saltern (Eilat, Israel)

The salinity responses of cyanobacteria, anoxygenic phototrophs, sulfate reducers, and methanogens from the laminated endoevaporitic community in the solar salterns of Eilat, Israel, were studied in situ with oxygen microelectrodes and in the laboratory in slurries. The optimum salinity for the sulfate reduction rate in sediment slurries was between 100 and 120 per thousand, and sulfate reduction was strongly inhibited at an in situ salinity of 215 per thousand. Nevertheless, sulfate reduction was an important respiratory process in the crust, and reoxidation of formed sulfide accounted for a major part of the oxygen budget. Methanogens were well adapted to the in situ salinity but contributed little to the anaerobic mineralization in the crust. In slurries with a salinity of 180 per thousand or less, methanogens were inhibited by increased activity of sulfate-reducing bacteria. Unicellular and filamentous cyanobacteria metabolized at near-optimum rates at the in situ salinity, whereas the optimum salinity for anoxygenic phototrophs was between 100 and 120 per thousand.     

绿原酸对凡纳滨对虾抗氧化系统及抗低盐度胁迫的影响

对绿原酸调节凡纳滨对虾(Litopenaeus vannamei)血淋巴抗氧化系统功能及抗低盐度胁迫的效果进行了评价。360尾凡纳滨对虾随机分为4组,分别投喂含有0、100、200和400 mg/kg绿原酸的饲料28 d,随后将对虾从盐度为32的天然海水直接转入至盐度为10的水中胁迫72 h。结果表明,在正常养殖条件下,绿原酸对凡纳滨对虾的成活率、血淋巴总抗氧化能力(Total antioxidative capacity, T-AOC)、超氧化物歧化酶(Superoxide dismutase, SOD)及过氧化氢酶(Catalase, CAT)活力均无明显影响,然而投喂含有绿原酸的饲料14 d,对虾血淋巴谷胱甘肽过氧化物酶(Glutathione peroxidase, GPx)活性和血淋巴细胞GPx和CAT基因表达水平均显著高于对照组(P<0.05);低盐度胁迫24 h,绿原酸组凡纳滨对虾的存活率较对照组提高10%,但各组之间无显著性差异(P>0.05);低盐度胁迫24 h,各组凡纳滨对虾血淋巴T-AOC、SOD和GPx活性与胁迫前相比均显著增加,说明低盐度胁迫条件下机体产生了抗氧化胁迫反应,同时绿原酸组对虾血淋巴GPx、CAT活性均显著高于对照组(P<0.05);低盐度胁迫72 h,绿原酸组对虾血淋巴T-AOC、GPx和CAT活性和血淋巴细胞GPx和CAT基因表达水平均明显高于对照组。上述结果表明绿原酸可有效调节凡纳滨对虾的抗氧化系统功能,增强对虾对于低盐度胁迫下的适应能力。