Reproductive patterns in the Antarctic brachiopod Liothyrella uva

first_imgThe reproductive cycle of the Antarctic articulate brachiopod Liothyrella uva (Broderip, 1833) is described from monthly samples collected between September 1985 and July 1987 from a population at Signy Island, Antarctica. Spermatogenesis and oogenesis are described for the first time in this species. Surface dried-tissue masses for a standard individual (41 mm shell length) were calculated for the digestive diverticula, gut, lophophore and gonad from monthly dissections of 15 brachiopods. Seasonal patterns, with summer peaks, were observed in the digestive diverticula and gut. The lophophore and gonad masses did not exhibit seasonal trends. Females showed a sharp decrease in proportion of large oocytes between October and November in 1986, suggesting spawning during this period. There was no similar decrease during the same period in 1985. Mean percent spermatozoa measurements revealed a large increase in November 1985 and a rapid decline in December 1985. This suggested a large spawning event for males in 1985 which was not repeated the following year. These data indicate large inter-annual differences in reproductive activity as well as differences between males and females. They also suggest the possibility of sperm storage by females. Brood characteristics were also highly variable. The smallest brooding female was 31.5 mm in length. Some females brooded more than one developmental stage simultaneously, and variation in brood size (numbers of embryos or larvae held in the lophophore) and brood composition between individuals was high. All samples collected throughout the 2 yr period contained some females with broods. The data suggest that the reproductive strategy of L. uva is highly plastic, and that there may be three reproductive periodicities on seasonal, annual and inter-annual time scales.last_img read more

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Draping or overriding: the effect of horizontal stress gradients on internal layer architecture in ice sheets

first_imgInternal isochronic layers in ice sheets sensed by radar show two characteristic relationships to the basal topography: Either they override it, with layers above the crests of rises lying essentially flat, or they drape over it, with the layers following rises and falls in basal topography. A mechanical theory is presented which shows that overriding is the expected behavior when topographic wavelengths are comparable with or less than the ice thickness, while draping occurs at longer wavelengths. This is shown with analytical perturbation solutions for Newtonian fluids, numerical perturbation solutions for nonlinear fluids, and finite element solutions for nonlinear fluids and large-amplitude variations. Bed variation from topography and changes in the basal boundary condition are considered, for fixed bed and sliding beds, as well as three-dimensional flows and thermomechanically coupled flows. In all cases, the dominant effect on draping/overriding is the wavelength of the topography or variation in basal boundary conditions. Results of these full mechanical system calculations are compared with those from the shallow ice approximation and the longitudinal stress approximation. Some calculations are carried out for zero accumulation, where the age of the ice and therefore isochrone geometry is not defined. It is shown that there is a close relationship between isochrones and streamlines, and that they behave similarly when bed wavelength divided by the ice thickness is small compared with the ratio of ice velocity and accumulation rate, which is a useful approximation. Numerical comparisons of isochrones and streamlines show them to be virtually coincident.last_img read more

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Antarctic precipitation and climate change predictions: Horizontal resolution and margin vs plateau issues

first_imgAll climate models participating in the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, as made available by the Program for Climate Model Diagnosis and Intercomparison (PCMDI) as the Coupled Model Intercomparison Project 3 (CMIP3) archive, predict a significant surface warming of Antarctica by the end of the 21st century under a moderate (SRESA1B) greenhouse-gas scenario. All models but one predict a concurrent precipitation increase but with a large scatter of results. The models with finer horizontal resolution tend to predict a larger precipitation increase. Because modeled Antarctic surface mass balance is known to be sensitive to horizontal resolution, extrapolating predictions from the different models with respect to model resolution mayprovide simple yet better multi-model estimates of Antarctic precipitation change than mere averaging or even more complex approaches. Using such extrapolation, a conservative estimate of the predicted precipitation increase at the end of the 21st century is +30 kgm–2 a–1 on the grounded ice sheet, corresponding to a >1mma–1 sea-level rise. About three-quarters of this rise originates from the marginal regions of the Antarctic ice sheet with surface elevation below 2250 m. This is where field programs are most urgently needed to better understand and monitor accumulation at the surface of Antarctica, and to improve and verify prediction models.last_img read more

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High divergence across the whole mitochondrial genome in the “pan-Antarctic” springtail Friesea grisea: Evidence for cryptic species?

first_imgCollembola are one of the few hexapod groups adapted to live in the harsh environmental conditions of Antarctic terrestrial ecosystems. Diversity is limited to a few species that can be very abundant in coastal deglaciated sites. A remarkable lack of overlap in Collembola species composition is evident between Western and Eastern Antarctica, and Friesea grisea is currently the only species whose distribution is thought to span these two main regions of the continent. However, our analysis of the complete sequences of the mitochondrial genomes from specimens obtained from each of the two regions showed unexpected genetic divergence, well above the average levels observed between populations belonging to the same species, and so indicating that these are actually separate species, despite their lack of distinguishing morphology. Detailed analysis of the two genomes showed the presence of a non-coding region observed between trnS (uga) and nad1. Other features of these mitochondrial genomes, such as base compositional bias, secondary structure features of tRNAs and the presence of regulatory elements in the control region, are described and discussed from an evolutionary standpoint. (C) 2009 Elsevier B.V. All rights reserved.last_img read more

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Estimating the location of the open-closed magnetic field line boundary from auroral images

first_imgThe open-closed magnetic field line boundary (OCB) delimits the region of open magnetic flux forming the polar cap in the Earth’s ionosphere. We present a reliable, automated method for determining the location of the poleward auroral luminosity boundary (PALB) from far ultraviolet (FUV) images of the aurora, which we use as a proxy for the OCB. This technique models latitudinal profiles of auroral luminosity as both a single and double Gaussian function with a quadratic background to produce estimates of the PALB without prior knowledge of the level of auroral activityor of the presence of bifurcation in the auroral oval. Wehave applied this technique to FUV images recorded by theIMAGE satellite from May 2000 until August 2002 to producea database of over a million PALB location estimates,which is freely available to download. From this database,we assess and illustrate the accuracy and reliability of this technique during varying geomagnetic conditions. We find that up to 35% of our PALB estimates are made from double Gaussian fits to latitudinal intensity profiles, in preference to single Gaussian fits, in nightside magnetic local time (MLT) sectors. The accuracy of our PALBs as a proxy for the location of the OCB is evaluated by comparison with particle precipitation boundary (PPB) proxies from the DMSP satellites. We demonstrate the value of this technique in estimating the total rate of magnetic reconnection from the time variation of the polar cap area calculated from our OCB estimates.last_img read more

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Interannual variability in effective diffusivity in the upper troposphere/lower stratosphere from reanalysis data

first_imgThe effective diffusivity based on passive tracer advection is used to evaluate the long-term mixing properties for the period 1980–2012 in the lower stratosphere and upper troposphere (UTLS) using data from the ERA-Interim reanalysis. The regions of strongest interannual variability in effective diffusivity coincide with the regions of strong climatological mixing, such as the winter and spring midlatitude stratosphere, the polar lowermost stratosphere and around the edge of the subtropical jets (especially in summer). The annular modes dominate the variability in the winter polar vortices, and the Quasi-Biennial Oscillation in the tropical stratosphere. El Niño/Southern Oscillation modulates the strength of mixing across the subtropical jets, and has a significant impact on mixing in the summer subtropical lower stratosphere. Long-term trends show a vertical shift in the mixing consistent with the effect of ozone depletion on the zonal wind in the austral summer polar stratosphere. Other significant trends include increased mixing in the austral surf zone and a dipolar pattern in the boreal summer and autumn, with mixing increased on the equatorward part of the subtropical jet and reduced just above. The results are highly consistent with those from the JRA-55 reanalysis when the same horizontal resolution is used. The calculations are also qualitatively consistent with effective diffusivity obtained directly from the potential vorticity field and, in the UTLS, they are broadly consistent with those obtained from the ozone field.last_img read more

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The development of a space climatology: 2. The distribution of power input into the magnetosphere on a 3‐hourly timescale

first_imgPaper 1 in this series (Lockwood et al., 2018a, https://doi.org/10.1029/2018SW001856) showed that the power input into the magnetosphere Pα is an ideal coupling function for predicting geomagnetic “range” indices that are strongly dependent on the substorm current wedge and that the optimum coupling exponent α is 0.44 for all averaging timescales, τ, between 1 min and 1 year. The present paper explores the implications of these results. It is shown that the form of the distribution of Pα at all averaging timescales τ is set by the interplanetary magnetic field orientation factor via the nature of solar wind‐magnetosphere coupling (due to magnetic reconnection in the dayside magnetopause) and that at τ = 3 hr (the timescale of geomagnetic range indices) the normalized Pα (divided by its annual mean, that is, τ=3hr/τ=1yr) follows a Weibull distribution with k of 1.0625 and λ of 1.0240. This applies to all years to a useful degree of accuracy. It is shown that exploiting the constancy of this distribution and using annual means to predict the full distribution gives the probability of space weather events in the largest 10% and 5% to within uncertainties of magnitude 10% and 12%, respectively, at the one sigma level.last_img read more

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Dixie State Men’s Basketball Ranks 9th Nationally In Division II Attendance

first_img Tags: Burns Arena/Dixie State men’s basketball/Jon Judkins/NCAA Division II/Northern State Written by July 9, 2018 /Sports News – Local Dixie State Men’s Basketball Ranks 9th Nationally In Division II Attendance FacebookTwitterLinkedInEmailST. GEORGE, Utah-Monday, Dixie State men’s basketball announced it ranked in the top 10 nationally in Division II attendance.Dating back to the 2008-09 season, the Trailblazers have annually ranked in the top 15 nationally in Division II.This season, the Trailblazers drew 26,309 fans in just 10 home dates, ranking second annually in the Pacific West Conference and the NCAA West region.Additionally, the Trailblazers finished second nationally in season attendance average at all games, drawing 2,630 supporters.The only team to beat them was Northern State (S.D.), as they led in both total attendance (55,980 fans over the course of 15 home games) and attendance average (3,732 fans).Among all eight NCAA schools in Utah, Dixie State ranked sixth as Brigham Young was the highest, averaging 14,230 fans per game and 227,692 total.The Trailblazers’ ardent home support has served them well as since going to Division II in the 2006-07 season, Dixie State has an 112-23 (.829) record under Jon Judkins at Burns Arena.This past season, Dixie State went 9-1 at home. Brad Jameslast_img read more

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51’s Crush Bees In Vegas

first_img Written by FacebookTwitterLinkedInEmail(Las Vegas, NV)  —  The Bees gave up 10 runs over the first two innings in a 13-6 loss to the 51’s in Las Vegas last night.Starter Osmer Morales gave up seven hits and six earned runs in less than two innings to take the loss.  Jose Fernandez homered in defeat.Game two of the three-game set gets going tonight. Tags: Baseball/PCL/Salt Lake Bees August 22, 2018 /Sports News – Local 51’s Crush Bees In Vegas Robert Lovelllast_img

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