3,328 research outputs found
Genetic diversity in wild stocks of the giant freshwater prawn (Macrobrachium rosenbergii): implications for aquaculture and conservation
The giant freshwater prawn (Macrobrachium rosenbergii) is cultured widely around the world but little is known about the levels and patterns of genetic diversity in either wild or cultured stocks. Studies have suggested that genetic diversity may be relatively low in some cultured stocks due to the history of how they were founded and subsequent exposure to repeated population bottlenecks in hatcheries. In contrast, wild stocks have an extensive distribution that extends from Southern Asia across Southeast (SE) Asia to the Pacific region. Therefore, wild stocks could be an important resource for genetic improvement of culture stocks in the future. Understanding the extent and patterns of genetic diversity in wild giant freshwater prawn stocks will assist decisions about the direction future breeding programs may take. Wild stock genetic diversity was examined using a 472 base-pair segment of the 16S rRNA gene in 18 wild populations collected from across the natural range of the species. Two major clades ("eastern" and "western") were identifi ed either side of Huxley’s line, with a minimum divergence of 6.2 per cent, which implies separation since the Miocene period (5-10 MYA). While divergence estimates within major clades was small (maximum 0.9 per cent), evidence was also found for population structuring at a lower spatial scale. This will be examined more intensively with a faster evolving mtDNA gene in the future
Genetic diversity in wild stocks of the giant freshwater prawn (Macrobrachium rosenbergii): implications for aquaculture and conservation
The giant freshwater prawn (Macrobrachium rosenbergii) is cultured widely around the world but little is known about the levels and patterns of genetic diversity in either wild or cultured stocks. Studies have suggested that genetic diversity may be relatively low in some cultured stocks due to the history of how they were founded and subsequent exposure to repeated population bottlenecks in hatcheries. In contrast, wild stocks have an extensive distribution that extends from Southern Asia across Southeast (SE) Asia to the Pacific region. Therefore, wild stocks could be an important resource for genetic improvement of culture stocks in the future. Understanding the extent and patterns of genetic diversity in wild giant freshwater prawn stocks will assist decisions about the direction future breeding programs may take. Wild stock genetic diversity was examined using a 472 base-pair segment of the 16S rRNA gene in 18 wild populations collected from across the natural range of the species. Two major clades ("eastern" and "western") were identifi ed either side of Huxley’s line, with a minimum divergence of 6.2 per cent, which implies separation since the Miocene period (5-10 MYA). While divergence estimates within major clades was small (maximum 0.9 per cent), evidence was also found for population structuring at a lower spatial scale. This will be examined more intensively with a faster evolving mtDNA gene in the future.Genetic diversity, Stocks, Nature conservation Macrobrachium rosenbergii
Low-frequency line temperatures of the CMB
Based on SU(2) Yang-Mills thermodynamics we interprete Aracde2's and the
results of earlier radio-surveys on low-frequency CMB line temperatures as a
phase-boundary effect. We explain the excess at low frequencies by evanescent,
nonthermal photon fields of the CMB whose intensity is nulled by that of Planck
distributed calibrator photons. The CMB baseline temperature thus is identified
with the critical temperature of the deconfining-preconfining transition.Comment: v2: 9 pages, 1 figure, extended discussion of why prsent photon mass
bounds are not in contradiction to a low-temperature, low-frequency Meissner
mass responsible for UEGE, matches journal versio
A joint study of early and late spectral distortions of the cosmic microwave background and of the millimetric foreground
We have compared the absolute temperature data of the CMB spectrum with
models for CMB spectra distorted by a single or two heating processes at
different cosmic times. The constraints on the fractional energy injected in
the radiation field, DE/E, are mainly provided by the FIRAS instrument aboard
the COBE satellite. Under the hypothesis that two heating processes have
occurred at different epochs, the limits on DE/E are relaxed by a factor 2 both
for the earlier and the later process with respect to the case in which a
single energy injection in the thermal history of the universe is considered.
In general, the constraints on DE/E are weaker for early processes than for
relatively late processes, because of the wavelength coverage of FIRAS data.
We considered also the FIRAS calibration as revised by Battistelli et al.
2000, that, in the case of the favourite calibrator emissivity law proposed by
the authors, implies significant deviations from a planckian spectrum. An
astrophysical explanation of this, although intriguing, seems difficult, both
in terms of CMB spectral distortions and in terms of a relevant millimetric
foreground.
Future precise measurements at longer wavelengths as well as current and
future CMB anisotropy space missions will provide independent, direct or
indirect, cross checks.Comment: 24 pages, 8 figures; includes improvements in response to refere
report. Accepted for publication on MNRA
The numerical solution of the Navier-Stokes equations for laminar incompressible flow past a paraboloid of revolution
A numerical method is presented for the solution of the Navier-Stokes equations for flow past a paraboloid of revolution. The flow field has been computed for a large range of Reynolds numbers. Results are presented for the skinfriction and the pressure together with their respective drag coefficients. The total drag has been checked by means of an application of the momentum theorem.
Taxonomic resolution of the ribosomal RNA operon in bacteria: Implications for its use with long-read sequencing
DNA barcoding through the use of amplified regions of the ribosomal operon, such as the 16S gene, is a routine method to gain an overview of the microbial taxonomic diversity within a sample without the need to isolate and culture the microbes present. However, bacterial cells usually have multiple copies of this ribosomal operon, and choosing the ‘wrong’ copy could provide a misleading species classification. While this presents less of a problem for well-characterized organisms with large sequence databases to interrogate, it is a significant challenge for lesser known organisms with unknown copy number and diversity. Using the entire length of the ribosomal operon, which encompasses the 16S, 23S, 5S and internal transcribed spacer regions, should provide greater taxonomic resolution but has not been well explored. Here, we use publicly available reference genomes and explore the theoretical boundaries when using concatenated genes and the full-length ribosomal operons, which has been made possible by the development and uptake of long-read sequencing technologies. We quantify the issues of both copy choice and operon length in a phylogenetic context to demonstrate that longer regions improve the phylogenetic signal while maintaining taxonomic accuracy
Fine-structure diagnostics of neutral carbon toward HE 0515-4414
New high-resolution high signal-to-noise spectra of the damped Lyman
(DLA) system toward the quasi-stellar object HE 0515-4414 reveal
absorption lines of the multiplets 2 and 3 in \ion{C}{i}. The resonance lines
are seen in two components with total column densities of
and , respectively. The comparision of theoretical
calculations of the relative fine-structure population with the ratios of the
observed column densities suggests that the \ion{C}{i} absorbing medium is
either very dense or exposed to very intense UV radiation. The upper limit on
the local UV energy density is 100 times the galactic UV energy density, while
the upper limit on the \ion{H}{i} number density is 110 cm. The
excitation temperatures of the ground state fine-structure levels of
and K, respectively, are consistent with the temperature-redshift
relation predicted by the standard Friedmann cosmology. The cosmic microwave
background radiation (CMBR) is only a minor source of the observed
fine-structure excitation.Comment: 5 pages, 5 figures, uses A&A macro package, gzipped tar archive,
accepted by A&
Synchronisation of sedimentary records using tephra : a postglacial tephrochronological model for the Chilean Lake District
Well-characterised tephra horizons deposited in various sedimentary environments provide a means of synchronising sedimentary archives. The use of tephra as a chronological tool is however still widely underutilised in southern Chile and Argentina. In this study we develop a postglacial tephrochronological model for the Chilean Lake District (ca. 38 to 42 degrees S) by integrating terrestrial and lacustrine records. Tephra deposits preserved in lake sediments record discrete events even if they do not correspond to primary fallout. By combining terrestrial with lacustrine records we obtain the most complete tephrostratigraphic record for the area to date. We present glass geochemical and chronological data for key marker horizons that may be used to synchronise sedimentary archives used for palaeoenvironmental, palaeoclimatological and palaeoseismological purposes. Most volcanoes in the studied segment of the Southern Volcanic Zone, between Llaima and Calbuco, have produced at least one regional marker deposit resulting from a large explosive eruption (magnitude >= 4), some of which now have a significantly improved age estimate (e.g., the 10.5 ka Llaima Pumice eruption from Llaima volcano). Others, including several units from Puyehue-Cordon Caulle, are newly described here. We also find tephra related to the Cha1 eruption from Chaiten volcano in lake sediments up to 400 km north from source. Several clear marker horizons are now identified that should help refine age model reconstructions for various sedimentary archives. Our chronological model suggests three distinct phases of eruptive activity impacting the area, with an early-to-mid-Holocene period of relative quiescence. Extending our tephrochronological framework further south into Patagonia will allow a more detailed evaluation of the controls on the occurrence and magnitude of explosive eruptions throughout the postglacial
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