Contractile and metabolic characteristics of muscle fibres from Antarctic fish

first_imgContractile properties were determined for muscles from three species ofAntarctic fish with broadly similar activity patterns:Trematomus hansoni, Notothenia rossii and Chaenocephalus aceratus. C. aceratus differs from theother species in that the genes for the respiratory pigments are not expressed. Red and white fibres were isolated from the pectoral fin adductor and trunkmuscles, respectively. Fibre segments were chemically skinned with the nonionicdetergent Brij-58. All experiments were carried out at 0°C. Maximum isometric tensions (Po) were 6.6–7.1 Ncm−2for red, and 21.4–25.1 Ncm−2 for white muscle fibres. The force-velocity (P-V) characteristics of musclefibres were determined by step isotonic releases. Unloaded contraction velocities (muscle lengths s−1, Los−1) were 0.7 for red, and 0.9?-1.1 for white fibres. Maximum mechanical power outputs (Wkg−1 muscle for white muscle), calculated using Hill’s equation for muscle shortening, were 26.7 (T.hansoni), 15.7 (N. rossii) and 22.7 (C. aceratus). Corresponding values forred pectoral muscle fibres were around 4.2 Wkg−1 for all three species. Maximum activities of enzymes of carbohydrate utilization (hexokinase, phosphofructokinase, lactate dehydrogenase), fatty acid metabolism (carnitine palmitoyl transferase, 3-OH acyl CoA dehydrogenase) and aerobicmitochondrial metabolism (cytochrome oxidase) were measured in musclehomogenates from C. aceratus and N. rossii at 0°C. Red pectoral musclefibres from C. aceratus and N. rossii had similar activities of cytochromeoxidase, carnitine palmitoyltransferase and glycolytic enzymes. Hexokinaseactivities were two times higher in the red fibres of C. aceratus than N. rossii, suggesting a greater capacity for aerobic glucose utilization in the former species. In spite of the lack of respiratory pigments, the metabolic and mechanicalcharacteristics of the swimming muscles in C. aceratus apppear to be similarto those of other Notothenioids. Power outputs and enzyme activities ofAntarctic fish muscle measured at 0°C are comparable to those for temperatespecies measured at 15 or 25°C, indicating a high degree of cold-adaptation ofboth energy-producing and energy-utilizing pathways.last_img read more

A revised age for the granites of the central Somuncura Batholith, North Patagonian Massif

first_imgThe age of the granites of the La Esperanza region of the Somuncura Batholith, North Patagonian Massif has been revised, based in part on RbSr whole-rock data obtained by reanalyzing samples from a previous study. The new ages are 258 ± 15 Ma for the Prieto Granodiorite and 259 ± 16 Ma for the Donosa Granite, both from the older La Esperanza plutonic complex, and 239 ± 4 Ma for the Calvo Granite, from the younger volcano-plutonic Dos Lomas complex. The initial 87Sr/86Sr ratios are all in the range 0.7070–0.7076. The ages probably correspond stratigraphically to Late Permian and Early Triassic for the two complexes, respectively, consistent with traditional geologic interpretation. Together with recently published Triassic ages from the Batholith of Central Patagonia, it is clear that the acidic volcano-plutonic associations of northern Patagonia are very latest Paleozoic and Mesozoic in age. They are not obviously related to terrane collision but are part of a Permo-Triassic acid magmatic province that extends throughout the central Andes and that preceded, or was associated with, the early rifting of Gondwana.last_img read more

Cold or drought – the lesser of two evils for terrestrial arthropods?

first_imgWater is an essential part of all living organisms and terrestrial arthropods are no exception. They have to balance water loss and water gain to and from their bodies, often over a wide range of environmental conditions. Water exists in the arthropod body in two main forms: free, bulk or freezable water (usually forming 65-75% of fresh weight), and unfreezable water (often inappropriately termed bound water) associated with membranes and other macromolecular structures. Many factors influence the body water content of arthropods from the physical environment and climatic effects to feeding activity, metabolism and life stage. Some species are adapted to withstand dehydration (loss of 17-89% of their body weight), whilst others enter a state of anhydrobiosis or dormancy induced by partial desiccation. Body water plays an important role in arthropod cold hardiness. Partial dehydration may significantly affect the cold resistance of both freezing tolerant and freezing susceptible forms. An increase in the quantity of unfreezable water in arthropods of both strategies may occur through the production of low molecular weight sugar alcohols (polyols), and desiccation promotes polyol (e.g. glycerol) synthesis in some species.Hibernating insects and other terrestrial arthropods may be threatened by lethal desiccation in their natural habitats, and in cold environments this may be in addition to the possibility of freezing, which could result in death. Whilst a 50% reduction in body water content may double the haemolymph osmolality in an arthropod, the effect of this on its supercooling ability will depend largely on the cryoprotectant concentration and the initial haemolymph osmolality. On the other hand, partial dehydration in winter may increase the supercooling capacity of micro-arthropods by reducing ice nucleator activity.Whilst the biochemical and physiological similarities of the effects of cold and drought may be obvious, it should not be overlooked that desiccation tolerant arthropods may be pre-adapted for freezing tolerance, Thus cold and drought should be viewed as not necessarily competing mortality factors in overwintering arthropods, but as producing complementary adaptations for aiding survival in some species.last_img read more

Survival of Heleomyza borealis (Diptera, Heleomyzidae) larvae down to -60oC

first_imgHeleomyza borealis Boh. (Diptera, Heleomyzidae) overwinters as larvae in Arctic habitats, where they may experience winter temperatures below − 15°C. The larvae freeze at c.− 7°C but in acclimation experiments 80% survived when exposed to − 60°C. Of the larvae exposed to between − 4 and − 15°C, only 3% pupated. However, when cooled to − 20°C this increased to 44%, with 4% emerging as adults. Larvae maintained at 5°C contained low levels of glycerol, sorbitol and trehalose, which did not increase with acclimation to low temperatures. However, levels of fructose increased from 6.1 μg mg−1 fw in control animals to 17 μg mg−1 fw when exposed to − 2°C for 1 week. Larval body water (2.2 ± 0.1 g/g dw, mean ± SD, n = 100) and lipid content (0.22 ± 0.002 g/g fw, mean ± SE) showed no significant change during acclimation to low temperatures. Larvae maintained at a constant 5°C survived for over 18 months with little loss of body mass (from 7.5 ± 1.2 to 7.0 ± 1.2 mg fw, mean ± SD, n = 20), but none pupated. Heleomyza borealis larvae appear to feed and grow until they reach a body mass of about 7.5 mg and then become dormant. They remain in this state until they experience a low temperature stimulus (< − 15°C) followed by a warm period (≈ 5°C). This ensures that the larvae pupate and adults emerge in early summer, allowing the maximum growing period before the following winter. Heleomyza borealis are adapted to survive long winters in a dormant larval state. They have a low metabolic rate, can conserve body water even at subzero temperatures but do not synthesize large quantities of cryoprotectants.last_img read more

Foraging strategies of chinstrap penguins at Signy Island, Antarctica: importance of benthic feeding on Antarctic krill

first_imgChinstrap penguins Pygoscelis antarctica are one of the major consumers of Antarctic krill Euphausia superba in the Southern Ocean. To examine their foraging strategy, we studied foraging trip patterns and diving behaviour of chinstrap penguins breeding at Signy Island, Antarctica, using time-depth recorders. Foraging trips of penguins could be divided into 2 groups, short diurnal (7.8 h) and longer overnight (19.9 h) trips, with diurnal trips (74%) being dominant in number (263 out of 355 trips). The diving depths of our study birds were much deeper (to 179 m) than previous studies on this species, with modal maximum dive depth at around 90 to 100 m. Diving patterns and profiles included typical pelagic dives, but also included series of consecutive square-wave shaped dives reaching similar maximum depth, the typical characteristics of benthic dives. These benthic-type dives were more abundant in diurnal foraging trips than overnight trips. Analysis of stomach contents showed that penguins on both types of trip fed almost exclusively on Antarctic krill. There was a positive relationship between indices of the proportion of benthic feeding and of foraging efficiency (stomach content mass divided by foraging trip duration). These results highlight the potential importance of benthic feeding on Antarctic krill, the first such recorded instance for chinstrap penguins. This previously undescribed foraging strategy by one of the major avian consumers of Antarctic krill provides a new insight into the predator-prey interactions of the Antarctic coastal marine ecosystem.last_img read more

Late Ordovician (Hirnantian) scolecodont clusters from the Soom Shale Lagerstatte, South Africa

first_imgMore than 20 partial scolecodout Clusters were recovered from the Soom Shale Lagerstatte, South Africa. The specimens were found in association with chitinozoans, algae, conodont apparatuses and the enigmatic needle-like fossil Siphonacis. The Family Xanioprionidae is identified and the species Xanioprion? n. sp. is distinguished. The Family Mochtyellidae is also identified and the new genus Synaptogenys and new species S. rietvleiensis are described. The specimens represent the first described scolecodonts from South Africa and the first apparatus-based taxonomic study of specimens from Gondwana. J. Micropalaeontol. 27(2): 147-159, November 2008.last_img

Linking regional variation of epibiotic bacterial diversity and trophic ecology in a new species of Kiwaidae (Decapoda, Anomura) from East Scotia Ridge (Antarctica) hydrothermal vents

first_imgWe analyzed the diversity of bacterial epibionts and trophic ecology of a new species of Kiwa yeti crab discovered at two hydrothermal vent fields (E2 and E9) on the East Scotia Ridge (ESR) in the Southern Ocean using a combination of 454 pyrosequencing, Sanger sequencing, and stable isotope analysis. The Kiwa epibiont communities were dominated by Epsilon- and Gammaproteobacteria. About 454 sequencing of the epibionts on 15 individual Kiwa specimen revealed large regional differences between the two hydrothermal vent fields: at E2, the bacterial community on the Kiwa ventral setae was dominated (up to 75%) by Gammaproteobacteria, whereas at E9 Epsilonproteobacteria dominated (up to 98%). Carbon stable isotope analysis of both Kiwa and the bacterial epibionts also showed distinct differences between E2 and E9 in mean and variability. Both stable isotope and sequence data suggest a dominance of different carbon fixation pathways of the epibiont communities at the two vent fields. At E2, epibionts were putatively fixing carbon via the Calvin-Benson-Bassham and reverse tricarboxylic acid cycle, while at E9 the reverse tricarboxylic acid cycle dominated. Co-varying epibiont diversity and isotope values at E2 and E9 also present further support for the hypothesis that epibionts serve as a food source for Kiwa.last_img read more

Statistical optimisation of growth conditions and diesel degradation by the Antarctic bacterium, Rhodococcus sp. strain AQ5‒07.

first_imgPetroleum pollution is a major concern in Antarctica due to the persistent nature of its hydrocarbon components coupled with the region’s extreme environmental conditions, which means that bioremediation approaches are largely inapplicable at present. The current study assessed the ability of the psychrotolerant phenol-degrader, Rhodococcus sp. strain AQ5-07, to assimilate diesel fuel as the sole carbon source. Factors expected to infuence the efciency of diesel degradation, including the initial hydrocarbon concentration, nitrogen source concentration and type, temperature, pH and salinity were studied. Strain AQ5-07 displayed optimal cell growth and biodegradation activity at 1% v/v initial diesel concentration, 1 g/L NH4Cl concentration, pH 7 and 1% NaCl during one-factor-at-a-time (OFAT) analyses. Strain AQ5-07 was psychrotolerant based on its optimum growth temperature being near 20 °C. In conventionally optimised media, strain AQ5-07 showed total petroleum hydrocarbons (TPH) mineralisation of 75.83%. However, the optimised condition for TPH mineralisation predicted through statistical response surface methodology (RSM) enhanced the reduction to 90.39% within a 2 days incubation. Our preliminary data support strain AQ5-07 being a potential candidate for real-feld soil bioremediation by specifcally adopting sludge-phase bioreactor system in chronically cold environments such as Antarctica. The study also confrmed the utility of RSM in medium optimisation.last_img read more

Cousins to sign with 3-year, $84-million deal with Vikings, sources say

first_img Beau Lund FacebookTwitterLinkedInEmailScott Clarke / ESPN Images(NEW YORK) — Former Redskins quarterback Kirk Cousins intends to sign a 3-year, $84 million deal with the Minnesota Vikings on Thursday, according to sources who have spoken to ESPN’s Adam Schefter.The deal will make Cousins the highest paid quarterback in the NFL, unseating Matthew Stafford of the Detroit Lions.Last season, Cousins threw for over 4000 yards (4093) for the third consecutive season. He also connected for 27 touchdowns and 13 interceptions, making him one of the more productive play callers in the league.But Cousins had an uncomfortable relationship with the Redskins, ever since he made his NFL debut for them as a fourth round draft pick in 2012. Despite ranking fourth in passing yards, sixth in passer rating, and eighth in touchdown passes during three years as Washington’s starter, from 2015 to 2018, he never signed a long term contract with the team. This spring, the Redskins had finally had enough, and, instead of negotiating with Cousins once again, they traded for Kansas City Chiefs quarterback Alex Smith, opening the door for Cousin’s departure. Cousins joins a talented Vikings team that went into the offseason with a glut of talented quarterbacks. But with Case Keenum going to the Broncos and Sam Bradford planning to sign with the Cardinals, Minnesota was forced to look elsewhere.Last season, Minnesota crashed out against the eventual Super Bowl champion Eagles in the NFC Championship game, but the addition of Cousins will make the Vikings an even more dangerous team. With the league’s top-ranked defense and a number of offensive weapons, from Adam Thielen to Stefon Diggs, Cousins and company will have their sights set on a championship.Copyright © 2018, ABC Radio. All rights reserved. Written bycenter_img March 13, 2018 /Sports News – National Cousins to sign with 3-year, $84-million deal with Vikings, sources saylast_img read more

Scoreboard roundup — 5/9/18

first_img Written by May 10, 2018 /Sports News – National Scoreboard roundup — 5/9/18 FacebookTwitterLinkedInEmailiStock/Thinkstock(NEW YORK) — Here are the scores from Thursday’s sports events:INTERLEAGUECleveland 6, Milwaukee 2Pittsburgh 6, Chicago White Sox 5L.A. Angels 8, Colorado 0Atlanta 5, Tampa Bay 2AMERICAN LEAGUETexas 5, Detroit 4, 10 InningsHouston 4, Oakland 1N.Y. Yankees 9, Boston 6Baltimore 5, Kansas City 3Toronto 5, Seattle 2NATIONAL LEAGUECincinnati 2, N.Y. Mets 1, 10 InningsChicago Cubs 13, Miami 4Philadelphia 11, San Francisco 3San Diego 2, Washington 1L.A. Dodgers 6, Arizona 3NATIONAL BASKETBALL ASSOCIATION PLAYOFFSBoston 114, Philadelphia 112Copyright © 2018, ABC Radio. All rights reserved.center_img Beau Lundlast_img read more