Temperature dependence and acclimatory response of amylase in the High Arctic springtail Onychiurus arcticus (Tullberg) compared with the temperate species Protaphorura armata (Tullberg)

first_imgAmylolytic activity was measured in whole body homogenates of High Arctic (Onychiurus arcticus) and temperate (Protaphorura armata) springtails (Collembola: Onychiuridae) in the temperature range 5–55°C. A pH of ca. 8 was optimum for amylolytic activity in both species. A higher weight-specific amylolytic activity was observed in P. armata. In O. arcticus, amylolytic activity depended on thermal acclimation, which increased during 2 and 9 weeks of cold acclimation (5°C) and decreased over 7 weeks of warming (15°C) of animals that were previously acclimated to cold for 2 weeks. In cold-acclimated O. arcticus, a slower decrease of amylolytic activity occurred with lowering of temperature in the range 5–20°C in comparison with warm-acclimated specimens and P. armata, which resulted in higher activity at 5°C. The activation energy calculated from an Arrhenius plot for P. armata was 68.7 kJ.mol−1. In O. arcticus it was between 30.2 and 61.5 kJ.mol−1, being lower in cold-acclimated samples. The temperature optimum for amylolytic activity was higher in the temperate species (40°C), whilst in O. arcticus it depended on the acclimation regime: it rose to 35°C after warm acclimation and decreased to 20°C after cold adaptation. The total soluble protein content of body tissues of O. arcticus also increased during cold acclimation. These differences between the two species suggest that amylolytic activity is an indicator of cold adaptation in the High Arctic O. arcticus.last_img read more

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Visual fields and foraging in procellariiform seabirds: sensory aspects of dietary segregation

first_imgRetinal visual fields were determined using an ophthalmoscopic reflex technique in two seabird species of the family Procellariidae: white-chinned petrel Procellaria aequinoctialis and antarctic prion Pachyptila desolata. The binocular fields of both species show a similar shape but they differ in size and in the position of the bill within the field. In white-chinned petrels the binocular field extends vertically through approximately 140 degrees and has a maximum width of approximately 40 degrees. The bill is placed approximately central within the field. The binocular field of the prions is approximately half this width and vertical extent, and the bill is placed close to the ventral edge. These differences in binocular field topography can be correlated with the different foraging techniques that these birds employ when seeking a similar diet within the same environment. White-chinned petrels pursue individual items both at the surface and while diving to moderate depths. Antarctic prions feed primarily by filtering items from surface waters. These differences in visual field topography mirror those found in different terrestrial bird species that primarily employ visual or tactile cues in the pursuit of food items. White-chinned petrel eyes and visual fields show features of an amphibious optical design similar to those found in penguins and albatrosses. Copyright (C) 2001 S. Karger AG. Basel.last_img read more

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Estimating juvenile copepod growth rates: corrections, inter-comparisons and recommendations

first_imgThe 2 most common experimental methods used to estimate rates of juvenile growth in marine copepods are the molt rate (MR) method, and the artificial cohort (AC) method. Recently, we showed the equations used in the MR method to be incorrect, and proposed a modified molt rate (MMR) method. Here, using statistical and model approaches, we compare the AC and MMR methods under various scenarios to quantify their errors. Although the AC and MMR methods both use a combination of field sampling and simulated in situ incubations to estimate somatic growth, they differ in several important characteristics. The AC method determines growth by the change in mean weight during incubation. Mean weight of copepods in the samples can be determined directly, or inferred from mean weight by life stage or from length–weight regressions. We show that substantial error is avoided only if weights are measured directly (ACdirect). The ACdirect method is insensitive to variable age within stage due to mortality or variable recruitment in the sampled population, an important advantage over the MMR method. However, the ACdirect method is sensitive to variation in growth rate during incubation, which does not affect the MMR method. We therefore recommend that most experimental estimates of growth rate should apply the ACdirect method, with the MMR as a suitable alternative provided its biases are considered. An indirect method based on life stage is biased and we no longer recommend it, and an indirect method based on length–weight regression provides an intermediate level of bias.last_img read more

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Food choice of Antarctic soil arthropods clarified by stable isotope signatures

first_imgAntarctic soil ecosystems are amongst the most simplified on Earth and include only few soil arthropod species, generally believed to be opportunistic omnivorous feeders. Using stable isotopic analyses, we investigated the food choice of two common and widely distributed Antarctic soil arthropod species using natural abundances of 13C and 15N and an isotope labelling study. In the laboratory we fed the isotomid springtail Cryptopygus antarcticus six potential food sources (one algal species, two lichens and three mosses). Our results showed a clear preference for algae and lichens rather than mosses. These results were corroborated by field data comparing stable isotope signatures from the most dominant cryptogams and soil arthropods (C. antarcticus and the oribatid mite Alaskozetes antarcticus). Thus, for the first time in an Antarctic study, we present clear evidence that these soil arthropods show selectivity in their choice of food and have a preference for algae and lichens above mosses.last_img read more

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Crenarchaea and phytoplankton coupling in sedimentary archives: Common trigger or metabolic dependence?

first_imgThe concentrations of chlorins (chlorophyll transformation products indicative of phytoplankton production) and crenarchaeol (a marker for Crenarchaea abundance) are significantly positively correlated (Spearman’s rank correlation coefficient r(s) > 0.75) in four core records from freshwater (Lake Baikal) and marine settings (Southern, Atlantic, and Arctic Oceans). This suggests a close relationship between Crenarchaea abundance and phytoplankton production. Degradation and transport mechanisms, as well as a common environmental trigger, may in part account for our observations, but these mechanisms alone cannot fully explain them. Instead our findings point to a metabolic dependence of Crenarchaea on resources released by phytoplankton, such as organic carbon or ammonium.last_img read more

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Utility of 18-kHz acoustic data for abundance estimationof Atlantic herring (Clupea harengus)

first_imgCurrent acoustic survey protocols for Atlantic herring (Clupea harengus) abundance estimation are principally dependent upon 38-kHz backscatter data. This can constitute a substantial problem for robust stock assessment when 38-kHz data are compromised. Research vessels now typically collect multifrequency data during acoustic surveys, which could be used to remediate such situations. Here, we investigate the utility of using 18- and 120-kHz data for herring abundance estimation when the standard 38-kHz approach is not possible. Estimates of herring abundance/biomass in the Celtic Sea (2007–2010) were calculated at 18, 38, and 120 kHz using the standard 38-kHz target-strength (TS) model and geometrically equivalent TS models at 18 and 120 kHz. These estimates were comparedto assess the level of coherence between the three frequencies, and 18-kHz-derived estimates were subsequently input into standard 38-kHz-based population models to evaluate the impact on the assessment. Results showed that estimates of herring abundance/ biomass from 18 and 38 kHz acoustic integration varied by only 0.3–5.4%, and acoustically derived numbers-at-age estimateswere not significantly (p . 0.05) different from 1:1. Estimates at 120 kHz were also robust. Furthermore, 18-kHz-derived estimates did not significantly change the assessment model output, indicating that 18-kHz data can be used for herring stock assessment purposes.last_img read more

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Polar marine biology science in Portugal and Spain: Recent advances and future perspectives

first_imgPolar marine ecosystems have global ecological and economic importance because of their unique biodiversity and their major role in climate processes and commercial fisheries, among others. Portugal and Spain have been highly active in a wide range of disciplines in marine biology of the Antarctic and the Arctic. The main aim of this paper is to provide a synopsis of some of the results and initiatives undertaken by Portuguese and Spanish polar teams within the field of marine sciences, particularly on benthic and pelagic biodiversity (species diversity and abundance, including microbial, molecular, physiological and chemical mechanisms in polar organisms), conservation and ecology of top predators (particularly penguins, albatrosses and seals), and pollutants and evolution of marine organisms associated with major issues such as climate change, ocean acidification and UV radiation effects. Both countries have focused their polar research more in the Antarctic than in the Arctic. Portugal and Spain should encourage research groups to continue increasing their collaborations with other countries and develop multi-disciplinary research projects, as well as to maintain highly active memberships within major organizations, such as the Scientific Committee for Antarctic Research (SCAR), the International Arctic Science Council (IASC) and the Association of Polar Early Career Scientists (APECS), and in international research projects.last_img read more

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Substorm-induced energetic electron precipitation: Impact on atmospheric chemistry

first_imgMagnetospheric substorms drive energetic electron precipitation into the Earth’s atmosphere. We use the output from a substorm model to describe electron precipitation forcing of the atmosphere during an active substorm period in April–May 2007. We provide the first estimate of substorm impact on the neutral composition of the polar middle atmosphere. Model simulations show that the enhanced ionization from a series of substorms leads to an estimated ozone loss of 5–50% in the mesospheric column depending on season. This is similar in scale to small to medium solar proton events (SPEs). This effect on polar ozone balance is potentially more important on long time scales (months to years) than the impulsive but sporadic (few SPE/year versus three to four substorms/day) effect of SPEs. Our results suggest that substorms should be considered an important source of energetic particle precipitation into the atmosphere and included in high-top chemistry-climate modelslast_img read more

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Combining stable hydrogen (δ2H) isotopes and geolocation to assign Scaly-sided Mergansers to moult river catchments

first_imgScaly-sided Mergansers Mergus squamatus breed on freshwater rivers in Far East Russia, Korea, and China, wintering on similar habitat in China and Korea, but information on their post-breeding moulting habitats remains elusive. We combined analysis of stable hydrogen isotope ratios (δ2H) in flight feathers from nesting females equipped with geolocators to test whether we could correctly identify their use of moulting rivers (which show a strong north–south gradient in river water δ2H characteristics) based on feather δ2H values. The results are the first ever to demonstrate a strong positive correlation (r 2 = 0.91) between measured river catchment water δ2H and feather δ2H from birds of known moulting location (from geolocation) in an avian piscivorous species. Furthermore, our δ2H results overwhelmingly supported previous determinations based on feather δ13C and δ15N measurements from the same individuals confirming that most Scaly-sided Mergansers of both sexes moulted on freshwater, although four non-breeding and failed breeding females (out of 21) and one male (out of six) apparently undertook moult migration to brackish and marine waters. The single case where the δ2H results contradicted previous isotopic evidence was likely due to birds eating migratory fish of marine provenance that migrate up freshwater rivers. These results confirm the potential power of feather δ2H to assign piscivorous birds to specific river catchment moult sites and the utility of using multiple stable isotopes to assign birds to moult habitat and location in potentially complex estuarine and brackish situations or where migratory prey may be used by birds in freshwater habitatslast_img read more

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Spatial distributions of nitric oxide in the Antarctic winter‐time middle atmosphere during geomagnetic storms

first_imgEnergetic electron precipitation leads to increased nitric oxide (NO) production in the mesosphere and lower thermosphere. NO distributions in the winter time, high‐latitude Southern hemisphere atmosphere during geomagnetic storms are investigated. NO partial columns in the upper mesosphere at altitudes 70–90 km and in the lower thermosphere at 90–110 km have been derived from observations made by the Solar Occultation For Ice Experiment (SOFIE) onboard the Aeronomy of Ice in the Mesosphere (AIM) satellite. The SOFIE NO measurements during 17 geomagnetic storms in 2008–2014 have been binned into selected geomagnetic latitude and geographic latitude/longitude ranges. The regions above Antarctica showing the largest instantaneous NO increases coincide with high fluxes of 30–300 keV precipitating electrons from measurements by the second generation Space Environment Monitor (SEM‐2) Medium Energy Proton and Electron Detector instrument (MEPED) on the Polar orbiting Operational Environmental Satellites (POES). Significant NO increases over the Antarctic Peninsula are likely due to precipitation of >30 keV electrons from the radiation belt slot region. NO transport is estimated using Horizontal Wind Model (HWM14) calculations. In the upper mesosphere strong eastward winds (daily mean zonal wind speed ~20–30 ms‐1 at 80 km) during winter transport NO‐enriched air away from source regions 1–3 days following the storms. Mesospheric winds also introduce NO poor air into the source regions, quenching initial NO increases. Higher up, in the lower thermosphere, weaker eastward winds (~5–10 ms‐1 at 100 km) are less effective at redistributing NO zonally.last_img read more

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