Utilization of energy substrates during calling activity in tropical frogs

Calling activity in frogs is energetically demanding to males because they usually perform at or near their physiological capacities. Metabolic fuel for muscle contractions during bouts of aerobic calling activity comes from carbohydrates and lipids that are stored in the trunk muscles. I monitored nightly calling performance in males of seven tropical frog species from two families, Hylidae and Leptodactylidae, and compared levels of glycogen and lipid in the trunk muscles from males collected before and after a three-hour period of calling activity. Trunk muscles from late-evening males in five species had up to 63% less glycogen than the trunk muscles from early-evening males; relatively little depletion was observed in two other species. Overall, glycogen reserves and rates of depletion were highest in species with very high calling rates. It was not possible to measure changes in the relatively large stores of lipid in the trunk muscles after only 3 h of calling. Nevertheless, intramuscular lipid stores probably provide a greater percentage of the energy needed for sound production than glycogen stores, and are largest in species with high calling rates. Received: 7 January 1997 / Accepted after revision: 20 July 1997     

Lactate formation in Callianassa californiensis and Upogebia pugettensis (Crustacea: Thalassinidea)

The ability to accumulate lactate as a result of laboratory exposure to anoxia was examined in 2 species of mud-dwelling shrimp, the ghost shrimp Callianassa californiensis and the mud shrimp Upogebia pugettensis. Hemolymph lactate accumulated to a much greater degree in the mud shrimp, even though the overall levels of lactate dehydrogenase activity were similar in tissues of the two species. Carbohydrate reserves, estimated as glycogen, were not significantly depleted in muscle or midgut gland of either species as a result of anoxic stress. The results are discussed in relation to possible metabolic strategies employed to cope with the hypoxic environment of these crustaceans.     

Lipid class and glycogen content of the lugworm Abarenicola pacifica in relation to age,growth rate and reproductive condition

We measured the levels of lipid classes (wax esters, triacylglycerides, free fatty acids, sterols, phospholipids) and levels of glycogen in a population of Abarenicola pacifica over a one-year period beginning shortly after recruitment. Glycogen and lipid contents were unrelated to growth rates as estimated by changes in average size of individuals in the cohort. There was no indication of seasonality in levels of any component, consistent with the hypothesis of Slobodkin and Richman that animals living in environments where food supplies are likely to be stable, such as subsurface deposit-feeders like A. pacifica, do not accumulate energy reserves. Instead, glycogen content increased gradually and most lipid classes decreased gradually over time. A notable exception was the triacylglyceride content, which showed a large increase associated with the formation of eggs. Triacylglyceride levels in older A. pacifica and in two other species of depositfeeding polychaetes showed similar trends. Measurement of triacylglyceride levels may provide an additional objective method, supplementing egg counts and egg size, of quantifying reproductive effort in deposit-feeders.     

Regulation of glycolytic enzymes in the marine invertebrateHalicryptus spinulosus (Priapulida) during environmental anoxia and exposure to hydrogen sulfide

A particularly strong reduction of metabolic activity is a precondition for long-term survival ofHalicryptus spinulosus von Siebold under anoxic habitat conditions because of its relatively low fuel reserves (mainly glycogen). The present study analyses the mechanism of this metabolic slow-down. For this purpose the effects of environmental anoxia and exposure to hydrogen sulfide on the activity and selected kinetic properties of glycolytic enzymes [glycogen phosphorylase (GP), pyruvate kinase (PK)] and the concentrations of fructose-2,6-bisphosphate in the body wall ofH. spinulosus were analysed. Anoxia and hydrogen sulfide exposure stimulated modifications of the properties of the enzymes, in both cases due to probable covalent modification of the enzyme proteins. Under both conditions phosphorylase activity was depressed by about 1/3, the result of changes in the percentage of enzyme in the activea-form as well as the total amount of enzyme activity expressed (a +b). Effects of anoxia on the properties of pyruvate kinase included reducedV _max , decreasedS _0.5 for phospho-enolpyruvate, changes inK _a for fructose-1,6-bisphosphate (an initial decrease was followed by a later increase). TheI ₅₀ forL-alanine of PK was extremely reduced under anoxia and showed an even greater sensitivity to the presence of hydrogen sulfide. Anoxia stimulated a slight reduction in the content of fructose-2,6-bisphosphate, whereas exposure to hydrogen sulfide caused a dramatic decrease of this allosteric activator of phos-phofructokinase. The study gives evidence that mechanisms of glycolytic rate depression are conserved within a wide variety of vertebrate and invertebrate phyla. With two exceptions (fructose-2,6-bisphosphate levels and alanine inhibition of PK) the responses to hydrogen sulfide were the same as those to anoxia, suggesting that at a metabolic level, the consequences of each stress on energy metabolism are similar.     

Effects of anoxia on the activities of pyruvate kinase and phosphoenolpyruvate carboxykinase,and the production of lactate and succinate in the intertidal pulmonate Onchidium tumidium

Onchidium tumidium, an intertidal pulmonate, has evolved to depend mainly on the formation of succinate, rather than lactate and opines, to survive in anoxia. For our study O. tumidum were collected from the mud flats of the mangrove swamp at Mandai, Singapore between 1988 and 1991. After 24 h of anoxic exposure, the lactate and succinate contents of the anoxic individuals were approximately 10 and 150 times, respectively, the corresponding values of the normoxic individuals. Alanine and acetate accumulations also occurred during anoxia, though to a much lesser extent. No propionate or octopine was detected. The depletion in aspartate content in O. tumidium could not account for the amount of succinate accumulated during anoxia. The succinate formed might have originated from glycogen involving the flow of carbon through the phosphoenolpyruvate (PEP) branch point of glycolysis. In support of such a hypothesis, results indicate that there was a decrease in the affinity of pyruvate kinase from O. tumidium exposed to 24h of anoxia to PEP to facilitate succinate formation through phosphoenolpyruvate carboxykinase (PEPCK). In comparison, the affinity of PEPCK from O. tumidium exposed to anoxia to PEP was apparently unaltered.     

Energy metabolism in the foot of the marine gastropod Nassa mutabilis during environmental and functional anaerobiosis

This study concerns the effects of oxygen deprivation due to incubation in oxygen free sea water (environmental anoxia) or exercise (functional anoxia) and of exposure to air on the mode of energy production in the foot of the whelk Nassa mutabilis. Additionally, energy metabolism of the foot muscle was investigated during exercise after different anoxia periods and during the subsequent recovery period. During environmental anoxia, phosphoarginine, glycogen and aspartate are broken down as substrates and alanine and succinate are formed as products. There was no production of D-lactate or octopine. The energy charge value fell after 24-h anoxia. Exposure to air resulted in only small changes in phosphoarginine and alanine levels, suggesting that oxygen uptake was impaired in the first phase of air exposure but that, later, aerial respiration kept pace with the energy demand. Exercise caused a dramatic decrease of phosphoarginine concentration, coupled with glycolytic ATP production via octopine formation. In the recovery period (after exercise), the level of phosphoarginine was rapidly restored. An anaerobic component was evident during recovery as shown by the accumulation of D-lactate. Thus, both terminal dehydrogenases, octopine- and lactate dehydrogenase, are active in the muscle, but under different physiological conditions. Octopine formation also took place when the whelks were subjected to exercise after 4 or 24 h of anoxia. In this case, glycolysis provided between 70 and 90% of the energy required since the phosphagen store had already been depleted during the anoxic period. When the work load was increased (greater number of leaps), it became evident that the action of arginine kinase and octopine dehydrogenase are not closely linked. First there was an increase of arginine and then later a condensation of arginine with pyruvate to form octopine.     

The glycogen turnover rate in mackerel muscles

Turnover rate of the glycogen glucose in the lateral trunk muscles and the liver was investigated in ¹⁴C-glucose injected mackerels, Scomber scombrus. High values were recorded for the red-muscle glycogen; the values were about 40 times lower in the white muscle and the liver. Results are discussed in relation to the assumed metabolic function of the red muscle in fishes.     

Biochemical adaptations of the mudskipper Boleophthalmus boddaerti to a lack of oxygen

Specimens of the mudskipper Boleophthalmus boddaerti, collected along the estuarine canal at Pasir Ris, Singapore between April 1987 and December 1989, were examined in the laboratory. After being exposed to environmental hypoxia for 6 h, no accumulation of lactate, alanine or succinate was observed in the muscle tissue of B. boddaerti. In addition, the blood lactate content and muscle creatine phosphate (CrP), adenosine triphosphate (ATP) and glycogen contents were not significantly different from those of the control. During normoxic recovery, oxygen debt repayment was only a small fraction of the oxygen deficit incurred during the 6 h of hypoxic exposure. Therefore, it would appear that B. boddaerti coped with environmental hypoxia by undergoing metabolic rate reduction. After anoxic exposure, the CrP, ATP and adenosine diphosphate (ADP) contents in the muscle tissue of B. boddaerti were significantly lower than the corresponding control values. Lactate accumulated in the blood and muscle tissue of the anoxic fish though the muscle energy charge and glycogen content remained constant. Hence, B. boddaerti was able to cope with such a period of anoxia without increasing its glycolytic rate. Succinate, which was not detected in the muscle tissue of the control and hypoxia-exposed fish, accumulated in significant quantities in the muscle tissue of B. boddaerti exposed to environmental anoxia and functional hypoxia. In the case of functional hypoxia, there was a significant decrease in the muscle glycogen content, and the muscle lactate content increased 17.3-fold, indicating that glycolysis was activated to provide the source of energy during muscular exercise.     

Mechanisms generating modification of benthos following tidal flat invasion by a Spartina hybrid.

Many coastal habitats are being substantially altered by introduced plants. In San Francisco Bay, California, USA, a hybrid form of the eastern cordgrass Spartina alterniflora is rapidly invading open mudflats in southern and central sections of the Bay, altering habitat, reducing macrofaunal densities, and shifting species composition. The invasion has resulted in significant losses of surface-feeding amphipods, bivalves, and cirratulid polychaetes, while subsurface feeding groups such as tubificid oligochaetes and capitellid polychaetes have been unaffected. In the present paper, we document the causes and mechanisms underlying the changes observed. Through a series of in situ manipulative experiments we examined the influence of hybrid Spartina canopy on a range of physical, chemical, and biological properties. The hybrid Spartina canopy exerted a strong influence on the hydrodynamic regime, triggering a series of physical, chemical, and biological changes in the benthic system. Relative to tidal flats, water velocity was reduced in hybrid patches, promoting deposition of fine-grained, organic-rich particles. The resulting changes in the sediment environment included increased porewater sulfide concentrations and anoxia, which led to poor survivorship of surface feeders such as bivalves, amphipods, and polychaetes. These are key taxa that support higher trophic levels including migratory shorebirds that feed on tidal flats. Altered flow in the Spartina canopy further contributed to changes in barnacle recruitment and resuspension of adult benthic invertebrates. Increased crab-induced predation pressure associated with Spartina invasion also contributed to changes in benthic invertebrate communities. Our results suggest that multiple physical, chemical, biotic, and trophic impacts of the Spartina invasion have resulted in substantial changes in benthic communities that are likely to have important effects on the entire ecosystem.     

Survival of the intertidal pulmonate Onchidium tumidium during short term and long term anoxic stress

Onchidium tumidium showed a triphasic response to anoxia. Twelve hours of anoxic exposure had no effect on the glycogen content in O. tumidium. However, there were significant increases in the alanine, lactate and succinate contents in the anoxic individuals. These were accompanied by a significant decrease in the ATP content. These results suggest that O. tumidium survived the first 12 h of anoxic exposure without increasing the glycolytic flux to compensate for the lower efficiency of ATP production through anaerobic pathways. Indeed, the fructose-2,6-bisphosphate (F-2,6-P₂) content and the percentage of phosphofruc-tokinase (PFK) associated with the subcellular particles remain unchanged in O. tumidium exposed to 12 h of anoxia. Hence, a reduction in the metabolic rate of these individuals might have occurred during such a period of anoxia. In contrast, in between 12 and 24 h of anoxic exposure, the glycogen content O. tumidium decreased significantly, and levelled off thereafter. A significant increase in the percentage of PFK associated with the subcellular particles was observed in individuals exposed to 24 h of anoxia. In addition, the F-2,6-P₂ content of these anoxic individuals increased significantly. Taken together, these two mechanisms could activate PFK and lead to a greater glycolytic flux. Beyond 24 h of anoxic exposure, survival of O. tumidium must have required considerable suppression of metabolism as accumulation of end products and depletions of glycogen and ATP had reached constant levels.     

重庆缙云山常绿阔叶林群落物种多样性与土壤因子的关系

探讨了缙云山常绿阔叶林物种多样性的变化特征，并运用去势典范对应分析(DCCA)方法，分析了不同样方中土壤因子与群落多样性指数之间的关系．结果表明：(1)17个样方中物种丰富度指数是草本层最高，均匀度指数是乔木层最高．(2)土壤含水量和水解氮与乔木层物种丰富度和均匀度相关性明显，有效磷和乔木层均匀度有明显相关；全氮含量和有机质含量与草本层物种的均匀度有明显相关．(3)多酚氧化酶活性和乔木层物种的均匀度有明显相关，转化酶活性与乔木层物种丰富度和均匀度均有一定相关，多酚氧化酶活性和酸性磷酸酶活性与草本层的物种均匀度和丰富度有明显相关．图2表3参20     

Carbohydrate metabolism during anoxia and post-anoxia recovery in Chasmagnathus granulata crabs maintained on high-protein or carbohydrate-rich diets

We assessed the effects of anoxia exposure and recovery on glycogen synthesis and mobilization, glucose uptake, and on the enzymes that control carbohydrate metabolism in the hepatopancreas of Chasmagnathus granulata crabs receiving either a carbohydrate-rich (HC) or a high-protein diet (HP). In both dietary groups, anoxia led to a reduction in glucose uptake and in glycogen synthesis, and to an increase in hepatopancreas glycogen mobilization and in hemolymph glucose concentration. During the first 4 h of exposure to anoxia, total glycogen phosphorylase (GPT) and a form activity increased in HP and HC crabs, leading to a decrease in hepatopancreas glycogen concentration. During recovery, HP and HC crabs rapidly restored the hemolymph glucose levels to pre-anoxia concentrations. In HC crabs, incorporation of ¹⁴C from glucose into glycogen increased gradually after 12 h in normoxia, leading to restoration of glycogen concentration. Also during recovery, the ratio of glycogen synthase I (GSI) to glycogen phosphorylase a (GPa) increased in the HC group. In turn, recovering HP crabs had two peaks of glycogen synthesis, related with two peaks in the ratio of GSI to GPa. Consequently, no mobilization of ¹⁴C-glycogen occurred in recovering HP animals. Anoxia in C. granulata induces a marked decrease in the synthesis of carbohydrate reserves that is accompanied by an increase in glycogen mobilization and in circulating glucose levels. During the recovery period, there is an activation of endergonic processes which cause a decrease in hemolymph glucose levels. In C. granulata, glycogen metabolism seems to be controlled by the ratio of the GSI form to the GPa form. In field conditions, theses changes in the metabolic pattern may result from environmental PO₂ availability. In the winter, C. granulata stays in its holes, where environmental PO₂ falls to zero. The carbohydrate or protein content of the diets administrated to the crabs seem to induce different metabolic adjustments during anoxia and recovery.     

Host glutamine synthetase activities in the giant clam—zooxanthellae symbiosis: effects of clam size,elevated ammonia and continuous darkness

Host tissues and zooxanthellae of the giant clam Tridacna gigas contained glutamine synthetase, with the highest transferase activities present in the gill, followed by the kidney, mantle, zooxanthellae, foot, heart and adductor muscle, in that order. Synthetase activities of glutamine synthetase in host tissues and zooxanthellae were in a similar order, but the differences were not so marked. Host tissues also contained hexokinase, glucose-6-phosphate dehydrogenase and malate dehydrogenase. Highest hexokinase activities were present in the heart, followed, in order, by the gill, mantle, adductor muscle and foot. Highest glucose-6-phosphate dehydrogenase activities were present in the gill, followed by the mantle, heart, adductor muscle and foot. All tissues assayed contained high malate dehydrogenase activities. There was no detectable glutamate dehydrogenase activity. Glutamine synthetase activity in gill and mantle tissue decreased by 1.6% with every 1 cm increase in clam size. Host glutamine synthetase activity decreased by 80% in gill tissue and by 45% in mantle tissue in clams which were maintained for 8 d in continuous darkness. Similar effects were found when clams were kept in light in the presence of elevated ammonia concentrations. It is suggested that both host and symbionts are nitrogen-deficient in small clams and that host glutamine synthetase plays a role in ammonia assimilation by the intact association.     

Substrate supply, fine roots, and temperature control proteolytic enzyme activity in temperate forest soils

Temperature and substrate availability constrain the activity of the extracellular enzymes that decompose and release nutrients from soil organic matter (SOM). Proteolytic enzymes are the primary class of enzymes involved in the depolymerization of nitrogen (N) from proteinaceous components of SOM, and their activity affects the rate of N cycling in forest soils. The objectives of this study were to determine whether and how temperature and substrate availability affect the activity of proteolytic enzymes in temperate forest soils, and whether the activity of proteolytic enzymes and other enzymes involved in the acquisition of N (i.e., chitinolytic and ligninolytic enzymes) differs between trees species that form associations with either ectomycorrhizal or arbuscular mycorrhizal fungi. Temperature limitation of proteolytic enzyme activity was observed only early in the growing season when soil temperatures in the field were near 4 degrees C. Substrate limitation to proteolytic activity persisted well into the growing season. Ligninolytic enzyme activity was higher in soils dominated by ectomycorrhizal associated tree species. In contrast, the activity of proteolytic and chitinolytic enzymes did not differ, but there were differences between mycorrhizal association in the control of roots on enzyme activity. Roots of ectomycorrhizal species but not those of arbuscular mycorrhizal species exerted significant control over proteolytic, chitinolytic, and ligninolytic enzyme activity; the absence of ectomycorrhizal fine roots reduced the activity of all three enzymes. These results suggest that climate warming in the absence of increases in substrate availability may have a modest effect on soil-N cycling, and that global changes that alter belowground carbon allocation by trees are likely to have a larger effect on nitrogen cycling in stands dominated by ectomycorrhizal fungi.     

Ammonia production and kinetic properties of glutamate dehydrogenase in the sipinculid Phascolosoma arcuatum exposed to anoxia

The amounts of total NH ₄ ⁺ detected in the external media in which Phascolosoma arcuatum had been exposed to various periods of anoxia were significantly greater than those in which the worms were exposed to normoxia for a similar period. The increased NH ₄ ⁺ production by P. arcuatum during anoxic exposure was unlikely to be due to an increased catabolism of adenine nucleotides or urea. In contrast, there were significant decreases in the concentrations of several free amino acids in the coelomic plasma and body tissues of individuals during the 48 h of anoxic exposure. The amount of NH ₄ ⁺ produced by the anoxic P. arcuatum could be accounted for by the decreases in the concentrations of aspartate or glycine. Increases in the catabolism of free amino acids (FAA), leading to the increased production of NH ₄ ⁺ , in P. arcuatum during anoxia were supported by the detection of significant changes in the kinetic properties of glutamate dehydrogenase (GDH), in the deaminating direction, from worms exposed to anoxia for 48 h. The apparent increase in the affinity of GDH from the anoxic worm to glutamate would bring about a greater deaminating activity at physiological concentrations of ths substrate. P. arcuatum used in these experiments were collected from the mangrove swamp at Mandai, Singapore between 1990 and 1993.     

胶州湾多毛类环节动物数量分布与环境因子的关系

根据1998~2002年胶州湾10个站各季度大型底栖动物调查结果,讨论了多毛类环节动物在各站出现种数、生物量、栖息密度与环境因子的关系.结果表明,海底底质是影响多毛类数量分布与变化的重要因子,沙质软泥有利于多毛类生长,而粗沙砾石底质多毛类分布较少;春季多毛类种数、生物量和栖息密度均较高;在一定条件下,盐度是多毛类的限制因子,当盐度升高时,其生物量和栖息密度呈增加趋势.图2表6参14     

Studies of some biochemical changes in the tissues of Catla catla (Hamilton), Labeo rohita (Hamilton) and Cirrhinus mrigala (Hamilton) exposed to NH3-N,NO2-N and NO3-N

Biochemical changes, total proteins, glycogen, aspartate and alanine (AAT and ALAT) amino transferases were studied with exposure of sublethal concentrations of NH3-N, NO2-N and NO3-N to the freshwater fish Catla catla (Hamilton), Labeo rohita (Hamilton) and Cirrhinus mrigala (Hamilton). Depletion in the food reserves and enzyme activity was observed in all the three fish species exposed to these toxicants. Hence, the concentrations of NH3, NO2 and NO3 in water need to be monitored in water quality in aquaculture practices.     

Influence of anoxia on adaptation of euryhaline polychaetes to hyposmotic conditions

The metabolic reactions ofArenicola marina andNereis diversicolor (both euryoxic and euryhaline polychaetes from the intertidal) to hyposmotic shock under anaerobic conditions were investigated in 1987–1988 using specimens from the East Frisian Wadden Sea. Although reductions in salinity were within the limits of tolerance under normoxic conditions, during anoxia they resulted in increased stress and a significant reduction in survival time. Both species were unable to sufficiently intensify anaerobic energy production to match the increased requirement for energy during adaptation to hyposmotic conditions. Moreover, as an adaptation to anoxic conditions, worms reduced their metabolic activity after the first 6 h. Thus, specimens remained more swollen than at the same reduction in salinity under normoxic conditions. InA. marina only the extracellular volume was reduced all be it to a limited extent.N. diversicolor probably reacted in the same or similar way. In both species, cells remained swollen. The concentrations of cellular free amino acids were not reduced; that means the main mechanism of cellular volume regulation was not activated under these conditions.     

Spatio-temporal variation of hydroids and polychaetes associated with Cystoseira amentacea (Fucales: Phaeophyceae)

The temporal and spatial distribution of hydroids (sessile fauna) and polychaetes (vagile) on the brown alga Cystoseira amentacea (Fucales: Phaeophyceae) have been studied in the mid-littoral zone of the Apulian coast (Italy). Samplings were carried out in February and July 1997, at 1.5 m depth, at three sites (Gargano, Costa Merlata and Otranto), about 200 km apart from each other. Three replicates per site were collected for polychaetes, and another three, for hydroids. Samples yielded 142,426 polyps belonging to 20 hydroid species and 3,088 polychaete specimens belonging to 58 species. Seasonal variations in abundance and number of species were evident in hydroids. The only species probably exclusive of Cystoseira (the hydroid Clytia viridicans) was present only in the summer. Polychaetes showed marked seasonal differences only at the Gargano site. Multivariate techniques were used to compare, in both periods, assemblages within and among sites. Analysis of similarity testing revealed that, for both polychaetes and hydroids, assemblage structures significantly differed among sites and between seasons. Thus, the null hypothesis that the distribution in time and space of the epifauna on the same algal species is homogeneous over a wide geographical scale has been rejected, in spite of the homogeneity of the substrate. In both groups, quantitative differences of a few species seemed to be more important than qualitative ones in determining the spatial separation of sites, the species pool remaining rather consistent. A small-scale variability among replicates was also detected, especially at Gargano, for hydroids. Since the epifauna can allow better comparisons among sites than the actual distribution of the algal species, both sessile and vagile epiphytes of Cystoseira can be considered valid tools for evaluating environmental changes on coastal hard-bottom communities.     

Glycogen storage in relation to the moult cycle in the two crustaceansEmerita asiatica andLigia exotica

InEmerita asiatica, the quantitative fluctuations in the glycogen content of the hepatopancreas were markedly related to the moult cycle. The glycogen content of the hepatopancreas was maximum during premoult stages. It has been suggested that reserve glycogen, in addition to meeting general metabolic needs, may be especially involved in the genesis of the sugar precursors of chitin. The marked fall in the hepatopancreas glycogen values following moulting is probably due to its utilization in chitin synthesis during and immediately following moulting. InE. asiatica, the storage of glycogen was found to be meagre in muscles, and muscle glycogen had no bearing on chitin synthesis during moulting. InLigia exotica, glycogen is stored to a lesser extent than inE. asiatica, and was found in connective tissue and muscles. Significant fluctuations were noted in glycogen values correlated with the phases in the moult cycle when chitin synthesis took place. InL. exotica, the hepatopancreas does not serve as a storage depot for glycogen related to chitin synthesis.