Temperature effects on summer growth rates in the Antarctic scallop, Adamussium colbecki

Annual growth rates of Antarctic marine organisms are low compared to their relatives from warmer waters. Previous studies hypothesise that high food availability during austral spring–summer may enable Antarctic invertebrates to attain comparatively high short-term growth rates despite the low temperature. Neither a temperature-growth experiment with juvenile Adamussium colbecki (Smith 1902) nor the comparison of A. colbecki summer growth rates with an empirical scallop specific growth-to-temperature relationship could confirm this hypothesis. Hence, summer growth rates of young, immature A. colbecki are strongly affected by temperature, i.e. no uncoupling from temperature.     

Antarctic scallop (Adamussium colbecki) annual growth rate at Terra Nova Bay

Adamussium colbecki is one of the most well-studied Antarctic molluscs. However, information on its growth rate is currently based on estimates from mark and recapture experiments and from growth-ring analyses. This paper provides the first estimates of the growth pattern of this scallop throughout a year, for individuals maintained under both natural field and laboratory conditions. Results show size-related differences in growth rate, both in the field and in aquaria, with scallops in Terra Nova Bay growing faster than those kept in aquaria. Growth performances were lower than those reported in the literature.     

Antarctic scallop (Adamussium colbecki) spatial population variability along the Victoria Land Coast, Antarctica

Along the Victoria Land Coast, the population structure of the Antarctic scallop (Adamussium colbecki) was studied in McMurdo Sound (New Harbor), Terra Nova Bay, and Wood Bay, on a latitudinal span of 3 degrees. At a large spatial scale, most relevant differences between the scallop populations are linked to their depth distributions. The McMurdo and Wood Bay populations show a shallower bathymetric distribution with maximum abundance between 5 and 15 m depth. In contrast, inside Terra Nova Bay, at sites with similar near-shore bathymetric profiles, the maximum biomass is found between 40 and 70 m. This difference can be related to the different ice-cover persistency characterising these two areas, being less at Terra Nova Bay than in the other localities. Differences arise also in the reproductive period: at McMurdo, it seems to occur early in the austral spring, while at Terra Nova Bay, mature females are observed at the beginning of February. Also at a small scale, in sites only a few miles from each other, the population structures inside Terra Nova Bay and Wood Bay vary in terms of abundance and size frequency distribution, suggesting various environmental and biological constraints. Among environmental factors, bottom features (slope, sediment grain size, organic content) and water-column food supply during the summer months may be considered. In addition, as Adamussium is preyed upon by starfishes and fishes, its abundance and population structure may be affected by predators and their abundance. Accepted: 7 August 2000     

Karyology of the Antarctic scallop Adamussium colbecki, with some comments on the karyological evolution of pectinids

Karyotype, location of the nucleolar organiser region (NOR) and heterochromatin presence and composition were studied in the Antarctic scallop Adamussium colbecki Smith, 1902. The karyotype exhibits 2n = 38 chromosomes with 11 pairs of metacentrics, 5 of submetacentrics, one subtelocentric and two telocentrics. Ag–NOR, CMA₃, DA/MM and NOR–FISH evidenced paracentromeric NORs on the short arm of 2nd pair chromosomes. Digestion with three restriction endonucleases followed by sequential staining with Giemsa, CMA₃ and DAPI evidenced on all chromosomes centromeric heterochromatin positive for both DAPI and CMA₃. In situ hybridisation analysis showed the presence of an AT-rich satellite DNA in the centromeric heterochromatin of several chromosomes. A mosaicism was detected in the germinal cell lines of one specimen, as in six of the 20 plates examined the set had 37 chromosomes with a missing pair of telocentrics and an unpaired metacentric. Comparison of the chromosome sets of all the pectinids studied to date and comparison with a phyletic tree obtained from molecular mitochondrial genes studies yielded good agreement between karyotype morphology and taxonomic classification.     

The SR Ca2+ ATPase of the Antarctic scallop Adamussium colbecki: cold adaptation and heavy metal effects

Cell calcium is accumulated in intracellular stores by sarco-endoplasmic reticulum Ca²⁺ ATPases functionally interacting with the membrane lipid environment. Cold adaptations of membrane lipids in Antarctic Sea organisms suggest possible adaptive effects also on sarco-endoplasmic reticulum Ca²⁺ ATPases. We investigated the SR Ca²⁺ ATPase of an Antarctic scallop, Adamussium colbecki, by characterising the enzyme activity and studying temperature effects. Ca²⁺ ATPase, assayed by following ATP hydrolysis, was thapsigargin- and vanadate-sensitive, showed maximum activity under 2 μM Ca²⁺, 200 mM KCl and pH 7.2, and had a K _M for ATP of 22 ± 7 μM. Temperature effects showed an Arrhenius inversion between −1.8 and 0°C, indicating cold adaptation, an Arrhenius break at 10°C, and a collapse above 20°C. A. colbecki accumulates high amounts of cadmium in the digestive gland; heavy metal effects on sarco-endoplasmic reticulum Ca²⁺ ATPases were therefore tested, finding an IC₅₀ = 0.9 μM for Hg²⁺ and 3 μM for Cd²⁺. Finally, SDS-PAGE analysis showed a main band at about 100 kDa, which was identified as sarco-endoplasmic reticulum Ca²⁺ ATPase after trypsin digestion, and accounted for 60% total protein. Accepted: 10 December 1998     

Defenses against oxidative stress in the Antarctic scallop Adamussium colbecki and effects of acute exposure to metals

Since a general pathway of toxicity induced bypollutants is the enhancement of reactive oxygenspecies, biochemical responses associated withvariations in the antioxidant cellular system havebeen often proposed as biomarkers ofpollutant-mediated toxicity associated with oxidativestress. Antarctic organisms live in an extremeenvironment characterized by low water temperature,high level of dissolved oxygen, presence of ice andstrong seasonal changes in light intensity andavailability of food, conditions which could influenceboth the formation of reactive oxygen species and themechanisms for their removal. In this respect andconsidering the utility of this as a key species formonitoring marine Antarctic environment it was ofinterest to investigate the antioxidant defense systemof the scallop Adamussium colbecki.The parameters examined in the digestive gland of thescallop were the concentration of glutathione and theactivity of several glutathione dependent andantioxidant enzymes (glyoxalase I and II, glutathioneS-transferases, glutathione peroxidases, glutathionereductase, catalase, superoxide dismutase). Very highlevels of catalase suggest a possible adaptation toAntarctic extreme conditions, while the highactivities of glutathione S-transferases are moreprobably related to the feeding behavior of Pectinids.Enzymes from Adamussium colbecki generallyappeared to be active at low temperatures but, with afew exceptions, their activities increased with risingtemperature. Exposure of A. colbecki tosublethal concentrations of Cu or Hg resulted in asignificant reduction in the levels of totalglutathione and in the activity of catalase andglutathione S-transferases. Antioxidant responses ofA. colbecki could represent a useful tool inassessing the biological impact of environmentalpollutants in the Antarctic ecosystems.     

Biochemical characterization of the antioxidant system in the scallop Adamussium colbecki, a sentinel organism for monitoring the Antarctic environment

 The scallop Adamussium colbecki can be profitably used for monitoring Antarctic coastal environments but its utility would be increased if chemical analyses of pollutants were integrated with data on their biological effects. Since oxidative stress is a common pathway of toxicity induced by xenobiotics, a preliminary biochemical characterization was carried out on the antioxidant system of this species and baseline data collected for future assessment of the anthropogenic impact in this remote area. The digestive gland and gills were investigated for levels of glutathione and the activity of several glutathione-dependent and antioxidant enzymes: gluthathione reductase, EC 1.6.4.2; glyoxalase I, EC 4.4.1.5; glyoxalase II, EC 3.1.2.6; gluthathione S-transferases, EC 2.5.1.18; Se-dependent, EC 1.11.1.9 and Se-independent, EC 2.5.1.18 gluta-thione peroxidases; catalase, EC 1.11.1.6; and super-oxide dismutase, EC 1.15.1.1. The same enzymatic activities were measured for comparison in the Mediterranean molluscs Mytilus galloprovincialis and Pecten jacobaeus. Very high levels of glutathione S-transferases were found in the digestive gland of both species of scallop compared to mussels, suggesting the importance of different feeding behaviour among these molluscs. However, catalase activity, much higher in Adamussium colbecki than in the Mediterranean molluscs, may represent a biochemical adaptation to the Antarctic marine environment with high levels of dissolved oxygen. Enzymes from the Antarctic species appeared to be generally more active at low temperatures but, with a few exceptions, their activities increased at higher temperatures. Received: 20 March 1996/Accepted: 29 May 1996     

Distribution of Antarctic benthic foraminifers settling on the pecten Adamussium colbecki

Summary Some benthic foraminifers in Explorers Cove, Antarctica, occur both in the sediment and on hard objects such as rocks and invertebrates. The abundances of four of these foraminiferal species have been measured from sediment samples and from the upper valve of the pecten Adamussium colbecki. The two calcareous species, Cibicides refulgens and Rosalina globularis were more abundant on the pecten shells than the sediment: the agglutinated species, Trochammina ochracea and T. malovensis were more abundant in the sediment. A zone of low foraminiferal density was observed around the outer margin of each shell, but no evidence of an influence of pecten feeding currents on the foraminiferal distributions was found. The size of the pecten shell influenced the density of epizoic foraminifers colonizing it; large shells (area >43 cm²) supported much higher densities than smaller ones.     

Purification and biochemical characterization of a cadmium metallothionein from the digestive gland of the Antarctic scallop Adamussium colbecki (Smith, 1902)

A cadmium-binding protein was purified from the digestive gland of the Antarctic scallop, Adamussium colbecki, and biochemically characterized. Purification procedures included gel permeation and anion exchange chromatography, followed by preparative polyacrylamide gel electrophoresis. Our results demonstrate that the A. colbecki cadmium-binding protein has the general properties of metallothioneins: low molecular weight of about 10 kDa, spectroscopic features typical of cadmium thiolate clusters and high metal (cadmium) content. Analysis of amino acid composition reveals the absence of aromatic amino acids, histidine, methionine and arginine. Asparagine and glutamine are also absent. The A. colbecki metallothionein shows high levels of glycine (14%), aspartic acid (14%), glutamic acid (11%) and a low lysine content (4%); the A. colbecki metallothionein shows a lower cysteine content (12%) compared to other metallothioneins (17–30%) purified from both vertebrate and invertebrate organisms. The presence of a metallothionein in the digestive gland of A. colbecki suggests that in cold-ocean-adapted molluscs the heavy metal homeostasis mechanisms may have evolved similarly to those of organisms living in temperate marine environments, although the A. colbecki cadmium-binding protein shows a typical amino acidic composition that might reflect a peculiar physiological role. Accepted: 7 August 2000     

A satellite DNA containing CENP-B box-like motifs is present in the antarctic scallop Adamussium colbecki

The DNA of the Antarctic scallop Adamussium colbecki was found to contain a highly repeated sequence identifiable upon restriction with endonuclease BglII. The monomeric unit - denominated pACS (about 170bp long) - was cloned. Southern blot hybridization yielded a ladder-like banding pattern, indicating that the repeated elements are tandemly arranged in the genome and therefore represent a sequence of satellite DNA.Sequence analysis of five different clones revealed the presence of various subfamilies, some of which showed a high degree of divergence. In each clone, regions homologous to the mammalian CENP-B box were observed. A region homologous to the CDEIII centromeric sequence of yeast was also found in one of the clones. These observations suggest a relationship of the pACS family to the centromeric area in A. colbecki.     

Organophosphate-resistant forms of acetylcholinesterases in two scallops--the Antarctic Adamussium colbecki and the Mediterranean Pecten jacobaeus

We describe the acetylcholinesterase polymorphisms of two bivalve molluscs, Adamussium colbecki and Pecten jacobaeus. The research was aimed to point out differences in the expression of pesticide-resistant acetylcholinesterase forms in organisms living in different ecosystems such as the Ross Sea (Antarctica) and the Mediterranean Sea. In A. colbecki, distinct acetylcholinesterase molecular forms were purified and characterized from spontaneously soluble, low-salt-soluble and low-salt-Triton extracts from adductor muscle and gills. They consist of two non-amphiphilic acetylcholinesterases (G(2), G(4)) and an amphiphilic-phosphatidylinositol-membrane-anchored form (G(2)); a further amphiphilic-low-salt-soluble G(2) acetylcholinesterase was found only in adductor muscle. In the corresponding tissues of P. jacobaeus, we found a non-amphiphilic G(4) and an amphiphilic G(2) acetylcholinesterase; amphiphilic-low-salt-soluble acetylcholinesterases (G(2)) are completely lacking. Such results are related with differences in cell membrane lipid compositions. In both scallops, all non-amphiphilic AChEs are resistant to used pesticides. Differently, the adductor muscle amphiphilic forms are resistant to carbamate eserine and organophosphate diisopropylfluorophosphate, but sensitive to organophoshate azamethiphos. In the gills of P. jacobaeus, amphiphilic G(2) forms are sensitive to all three pesticides, while the corresponding forms of A. colbecki are sensitive to eserine and diisopropylfluorophosphate, but resistant to azamethiphos. Results indicate that organophosphate and/or carbamate resistant AChE forms are present in species living in far different and far away environments. The possibility that these AChE forms could have ensued from a common origin and have been spread globally by migration is discussed.     

Stenotherms at sub-zero temperatures: thermal dependence of swimming performance in Antarctic fish

We examined the burst swimming performance of two Antarctic fishes, Trematomus bernacchii and T. centronotus, at five temperatures between -1 degrees C and 10 degrees C. As Antarctic fishes are considered one of the most cold specialised and stenothermal of all ectotherms, we predicted they would possess a narrow thermal performance breadth for burst swimming and a correlative decrease in performance at high temperatures. Burst swimming was assessed by videotaping swimming sequences with a 50-Hz video camera and analysing the sequences frame-by-frame to determine maximum velocity, the distance moved throughout the initial 200 ms, and the time taken to reach maximum velocity. In contrast to our prediction, we found both species possessed a wide thermal performance breadth for burst swimming. Although maximum swimming velocity for both T. bernacchii and T. centronotus was significantly highest at 6 degrees C, maximum velocity at all other test temperatures was less than 20% lower. Thus, it appears that specialisation to a highly stable and cold environment is not necessarily associated with a narrow thermal performance breadth for burst swimming in Antarctic fish. We also examined the ability of the Antarctic fish Pagothenia borchgrevinki to acclimate their burst-swimming performance to different temperatures. We exposed P. borchgrevinki to either -1 degrees C or 4 degrees C for 4 weeks and tested their burst-swimming performance at four temperatures between -1 degrees C and 10 degrees C. Burst-swimming performance of Pagothenia borchgrevinki was unaffected by exposure to either -1 degrees C or 4 degrees C for 4 weeks. Maximum swimming velocity of both acclimation groups was thermally independent over the total temperature range of 1 degrees C to 10 degrees C. Therefore, the loss of any capacity to restructure the phenotype and an inability to thermally acclimate swimming performance appears to be associated with inhabiting a highly stable thermal environment.     

Field swimming performance of bluegill sunfish,Lepomis macrochirus: implications for field activity cost estimates and laboratory measures of swimming performance

Mobility is essential to the fitness of many animals, and the costs of locomotion can dominate daily energy budgets. Locomotor costs are determined by the physiological demands of sustaining mechanical performance, yet performance is poorly understood for most animals in the field, particularly aquatic organisms. We have used 3‐D underwater videography to quantify the swimming trajectories and propulsive modes of bluegills sunfish (Lepomis macrochirus, Rafinesque) in the field with high spatial (1–3 mm per pixel) and temporal (60 Hz frame rate) resolution. Although field swimming trajectories were variable and nonlinear in comparison to quasi steady‐state swimming in recirculating flumes, they were much less unsteady than the volitional swimming behaviors that underlie existing predictive models of field swimming cost. Performance analyses suggested that speed and path curvature data could be used to derive reasonable estimates of locomotor cost that fit within measured capacities for sustainable activity. The distinct differences between field swimming behavior and performance measures obtained under steady‐state laboratory conditions suggest that field observations are essential for informing approaches to quantifying locomotor performance in the laboratory.     

Comparison of muscle force,muscle endurance,and electromyogram activity during an expedition at high altitude

Handgrip force (HF), maximal pinch force (MF), muscle endurance (ME), and the median power frequency (MdPF) of the activity shown in the electromyogram (EMG) were studied at various altitudes in eight normal healthy subjects. MF and ME were measured between the index finger and thumb, and all measurements were obtained at altitudes ranging from 610 to 4860 m during an expedition in the Qinghai Plateau in China. With the change in altitude HF, ME, and MF showed no significant change. Compared to the MdPF at 2260 m on ascent, the MdPF at other altitudes showed a significant decrease (P<0.01). Thus, we conclude that muscle performance (HF, MF, and ME) was not affected by the environment at high altitude. However, MdPF was affected and the mean MdPF at 610 m after the expedition did not recover to initial values of MdPF. We suggest these results may have been affected by fatigue and chronic exposure to the hypobaric hypoxic environment, since the members of the expedition party expressed feelings of sluggishness and fatigue after the expedition.     

Adaptation of the dark muscle of cod to swimming activity

After cod ( Gadus morhua L.) had been exercised in a channel, the intensity of pigmentation of the dark muscle was shown to be greater than in unexercised controls. A well-marked seasonal cycle in pigmentation occurs in cod caught near Aberdeen with a summer maximum suggesting maximal feeding activity. The possibility of using the observation to identify stocks of fish is considered.     

Seasonal changes in fast-starts in the short-horn sculpin: integration of swimming behaviour and muscle performance

In short-horn sculpin Myoxocephalus scorpius , the power requirements for fast-start swimming and the length-specific velocity of the curvature wave travelling down the spine ( Û ) were not influenced significantly by acclimation to summer and winter conditions at test temperatures of 5 and 15° C. However, in-vivo and in-vitro muscle performance exhibited acclimation responses at 15° C. Seasonal acclimation altered the escape performance curves for power and Û significantly over a wider temperature range of 0·8–20° C. Û was significantly higher at 20° C in the summer- than winter-acclimation group. The acclimation of lower levels of physiological organization at 15° C may thus serve to extend the thermal limits for escape performance in summer acclimated fish.