The accumulation of fluorescent age pigments in the trochid gastropod Monodonta lineata

first_imgSeveral recent studies have shown the potential value of chloroform-soluble fluorescent age pigments (FAPs) in determining the age of marine invertebrates with no permanent hard parts. The primary assumption in estimating age from FAPs is that there is a linear (or at least monotonie) increase in FAP content with time. We have tested this assumption with the trochid gastropod Monodonta lineata, a species whose age can be established unequivocally from shell growth checks. Samples of 10 age classes (1.5–10.5 yr) were obtained and FAPs extracted from lyophilised cerebral ganglia and digestive gland. The fluorescence emission spectra were similar to those reported for other organisms, though the wavelength of maximum intensity varied with tissue, sex and age. Cerebral ganglia often showed two major emission peaks, digestive gland only one. Thin-layer chromatography indicated that at least three fluorescent compounds were present in the extracts. Digestive gland total FAP content did not vary for the first 5 yr of growth, but then trebled during the next 5 yr. The tissue concentration of FAP showed no statistically significant trend. Cerebral ganglia total FAP content increased during the first 5 yr then remained constant for the next 3 yr before declining. There was a steady decline in the concentration of cerebral ganglion FAP throughout life. These patterns indicate a complex relationship between FAP content and calendar age, and indicate that (at least in Monodonta) FAPs have little practical value for determining age.last_img read more

A new code for electrostatic simulation by numerical integration of the Vlasov and Ampere equations using MacCormack’s method

first_imgWe present anewsimulationcode for electrostatic waves in one dimension which uses the Vlasovequation to integrate the distribution function and Ampère’sequation to integrate the electric field forward in time. Previous Vlasovcodes used the Vlasov and Poisson equations. Using Ampère’sequation has two advantages. First, boundary conditions do not have to be set on the electric field. Second, it forms a logical basis for an electromagnetic code since the time integration of the electric and magnetic fields is treated in a similar way. MacCormack’smethod is used to integrate the Vlasovequation, which was found to be easy to implement and reliable. A stability analysis is presented for the MacCormack scheme applied to the Vlasovequation. Conditions for stability are more stringent than the simple Courant–Friedrich’s–Lewy (CFL) conditions for the spatial and velocity grids. We provide a simple linear function which when combined with the CFL conditions should ensure stability. Simulation results for Landau damping are in excellent agreement with numerical solutions of the linear dispersion relation for a wide range of wavelengths. The code is also able to retain phase memory as demonstrated by the recurrence effect and reproduce the effects of particle trapping. The use of Ampère’sequation enables standing and traveling waves to be produced depending on whether the current is zero or non-zero, respectively. In simulations where the initial current is non-zero and Maxwell’sequations are satisfied initially, additional standing waves may be set up, which could be important when the coupling of wave fields from a transmitter to a plasma is considered.last_img read more

Psychological selection of Antarctic personnel: the “SOAP” instrument

first_imgINTRODUCTION: The potential advantage of including a psychological test battery in the selection process for service in the Antarctic was examined in 348 applicants for employment in Antarctica with the British Antarctic Survey (BAS). METHODS: Applicants were screened with the Selection of Antarctic Personnel battery (SOAP) consisting of nine well-known psychological instruments. The SOAP scores were not revealed to the BAS selection panel members, who based the selection on operational criteria, interview, and a general medical examination. The SOAP scores of those selected (n = 177) were further compared with station commanders’ reports of winter adaptation (n = 140), and subjective health complaints (SHC) (n = 86). RESULTS: There were no significant agreements between SOAP scores (n = 348) and those actually selected by the BAS panel (121 accepted, 227 not accepted) (Cohen’s Kappas for inter-rater agreement < 0.20). Participants characterized as exceptionally well adapted by the station commanders had higher scores on Openness on the NEO-FFI (the "Big Five" personality inventory) [Odds Ratio (OR) = 5.2], and higher levels of Emotion-Focused Coping (OR = 2.7) and fewer SHC (OR = 0.3). Participants rated by station commanders as "poor" had higher levels of Defensive Hostility (OR = 4.2), and lower levels of Emotion-Focused Coping (OR = 0.3). Women had higher rates of success in service than men, but were less likely to be selected. DISCUSSION AND CONCLUSION: Adding a psychological test battery would improve the odds of selecting good performers, and reduce the odds of selecting poor performers.last_img read more

Widespread amplification of amplified fragment lengthpolymorphisms (AFLPs) in marine Antarctic animals

first_imgAlthough recent years have witnessed a rapidgrowth in the number of genetic studies of Antarctic organisms,relatively few studies have so far used nuclear markers,possibly due to the perceived cost and diYculty ofisolating markers such as microsatellites. However, anoften overlooked alternative is to use ampliWed fragmentlength polymorphisms (AFLPs), a versatile and low-costmethod capable of generating large numbers of predominantlynuclear loci in virtually any organism. We conducteda literature review of population genetic studies of Antarcticorganisms, Wnding that fewer than 10% used AFLPs.Moreover, a strong taxonomic bias was found, with studiesemploying mitochondrial DNA or microsatellites focussingpredominantly on animals, while those using AFLPs weremostly of plants or lower organisms. Consequently, weexplored the extent to which AFLPs amplify across a rangeof Antarctic marine animal taxa by genotyping eight individualseach of twelve diVerent species, ranging from echinodermsthrough soft corals to pelagic Wsh, at four selectiveprimer combinations. AFLPs readily ampliWed across all ofthe taxa, generating between 32 and 84 loci per species,with on average 56.5% of these being polymorphic. In general, levels of polymorphism bore little relationship with expectations based on larger populations of broadcastspawning species being more variable, though we did find a tentative positive correlation between the number of AFLP bands ampliWed and a measure of eVective population size. Our study lends further support for the utility and ease of use of AFLPs and their suitability for studies of Antarctic species across a wide range of taxa.last_img read more

Oxygen isotope anomaly not present in water vapor from Alert, Canada

first_imgLin et al. (1) claim to have discovered a positive 17O anomaly in water vapor from Alert, Canada, indicative of a component of stratospheric origin. However, their data (Tables S1−S5) do not support that assertion. Their finding of Δ17O = 76 ± 16 ppm (2 SE) in the Alert samples is relative to a reference fractionation line [designated Chicago local precipitation (CLP)] of much lower precision [slope 0.529 ± 0.003, ordinate axis intercept 70 ± 33 ppm from Vienna Standard Mean Ocean Water (VSMOW) on the logarithmic form of the oxygen triple-isotope plot] than is the norm for investigations that characterize Δ17O values at the parts per million …last_img read more

On the Seasonal Signal of the Filchner Overflow, Weddell Sea, Antarctica

first_imgThe cold ice shelf water (ISW) that formed below the Filchner–Ronne Ice Shelf in the southwestern Weddell Sea, Antarctica, escapes the ice shelf cavity through the Filchner Depression and spills over its sill at a rate of 1.6 Sverdrups (Sv; 1 Sv ≡ 106 m3 s−1), thus contributing significantly to the production of Weddell Sea Bottom Water. Here, the authors examine all available observational data from the region—including five year-long time series of mooring data from the Filchner sill—to examine the seasonal variability of the outflow. The temperature of the ISW outflow is found to vary seasonally by 0.07°C with a maximum in April. The accompanying signal in salinity causes a seasonal signal in density of 0.03–0.04 kg m−3, potentially changing the penetration depth of the ISW plume by more than 500 m. Contrary to recent modeling, the observations show no seasonal variability in outflow velocity. The seasonality observed at the sill is, at least partly, due to the admixture of high-salinity shelf water from the Berkner Bank. Observations and numerical modeling suggest, however, seasonal signals in the circulation upstream (i.e., in the ice shelf cavity and in the Filchner Depression) that—although processes and linkages are unclear—are likely to contribute to the seasonal signal observed at the sill. In the plume region downstream of the sill, the source variability is apparent only within the very densest portions of the ISW plume. In the more diluted part of the plume, the source variability is overcome by the seasonality in the properties of the water entrained at the shelf break. This will have implications for the properties of the generated bottom waters.last_img read more

Mangrove rhizosphere soils: a unique natural source of pravastatin-producing Penicillium microfungi

first_imgThe pravastatin-producing potential of rhizosphere soil microorganisms from mangrove forests has not been investigated in detail. In this study, a total of 20 Penicillium isolates were tested for pravastatin production. Six strains were able to synthesize pravastatin directly. Among these, the isolate Penicillium sp. ESF19M was the most active pravastatin producer with a yield of 28.43 mg/L. Molecular identification of this strain showed the highest homology with Penicillium citrinum.last_img

Small-scale deformation of an Arctic sea ice floe detected by GPS and satellite imagery

first_imgSmall-scale (~100 to 200 m) deformations of an Arctic sea ice floe were detected from multiple GPS-equipped buoys that were deployed on the same ice floe. Over a nine-month period three deformation events were recorded. At each case the event was of limited duration, each lasting less than a day. The events were highly compressive in nature with the area occupied by the buoy array decreasing by over half of the original area. The strain rate during the deformation, of the order of 10−5 s−1, is about three orders of magnitude larger than previous estimates for brittle fracturing for cracks of about 100 m in length. On the 2-day time scale, the strain rate became too small and none of the deformation events could be detected. This suggests that satellite data with longer time scales may significantly underestimate the amount of intermittent, small-scale brittle failure of total deformation. Taken as a whole, our results show the influence that large-scale wind stress can have on small-scale deformation. However, it is important to note that the impact of large-scale wind stress is also dependent on the properties of sea ice as well as on the spatial and temporal evolution of the underlying forces that influence the fracturing processlast_img read more

Precipitation instruments at Rothera Station, Antarctic Peninsula: a comparative study

first_imgDirect measurement of precipitation in the Antarctic using ground-based instruments is important to validate the results from climate models, reanalyses and satellite observations. Quantifying precipitation in Antarctica faces many unique challenges such as wind and other technical difficulties due to the harsh environment. This study compares a variety of precipitation measurements in Antarctica, including satellite data and reanalysis fields atRothera Station, Antarctica Peninsula. The tipping bucket gauges (TBGs) were less sensitive than laser-based sensors (LBSs). The most sensitive LBS (Visibility and Present Weather Sensor, VPF-730) registered 276 precipitation days, while the most sensitive TBG (Universal Precipitation Gauge, UPG-1000) detected 152 precipitation days. Case studies of the precipitation and seasonal accumulation results show the VPF-730 to be the most reliable precipitation sensor of the evaluated instruments. The precipitation amounts given by the reanalyses were positively correlated with wind speed. The precipitation from the Japanese 55-year Reanalysis was most affected by wind speed. Case studies also show that during low wind periods, precipitation measurements from the instruments were very close to the precipitation measurement given by the Global Precipitation Climatology Project (GPCP) 1-degree-daily (1DD) data. During strong wind events, the GPCP 1DD did not fully capture the effect of wind, accounting for the relatively small precipitation amount. The Laser Precipitation Monitor (LPM) and Campbell Scientific-700 (CS700H) experienced instrumental errors during the study, which caused the precipitation readings to become exceedingly high and low, respectively. Installing multiple LBSs in different locations (in close proximity) can help identify inconsistency in the readings.last_img read more

A rare observation of group prey processing in wild leopard seals (Hydrurga leptonyx)

first_imgCooperative feeding is often observed among predators with strong social bonds; however, it is unexpected in solitary predators. During 2016, several mass predation events were witnessed in St Andrews Bay and Right Whale Bay, South Georgia, where up to 36 leopard seals (Hydrurga leptonyx) were seen feeding together at king penguin (Aptenodytes patagonicus) colonies. Three post-mortem prey-processing events were observed where two leopard seals actively fed on the same carcass in an unusual display of tolerance for a species where anti-social behaviour is the norm. The seals were observed repeatedly tearing adult king penguins between themselves, while floating alongside each other at the surface of the water. This is the first record of co-feeding in this difficult-to-study species; however, it is expected that the behaviour is rare within the population. We propose that the high density of predators combined with the readily available prey, makes it costlier to defend a kill than it is to tolerate kleptoparasitism. It is unclear whether this behaviour shows cooperative feeding, which would likely enable more efficient prey processing: by holding the prey in their jaws, each seal provides an anchor on the prey that others can pull against to stretch and tear it.last_img read more