2,138 research outputs found
High level of hybridisation in three species of Indian major carps
Thirty individuals of each species of Indian major carps, i.e., Catla catla, Cirrhinus cirrhosus (C. mrigala) and Labeo rohita, obtained from a nursery near Mymensingh, Bangladesh were analysed by means of allozyme electrophoresis. Twenty-one loci were studied. Several loci revealed significant deviation from Hardy-Weinberg expectations caused by deficiency of heterozygotes, indicating Wahlund effects due to problems with species identification. Moreover, bimodal distributions of individual heterozygosity within the three putative species indicated hybridisation. This was confirmed using analysis of individual admixture proportions, as individuals misidentified to species and hybrids between species were observed. Furthermore, factorial correspondence analysis to visualize genetic relationships among individuals revealed three distinct groups containing misclassified individuals, along with some intermediate individuals interpreted as hybrids. Ten per cent of all C. catla and L. rohita had been erroneously identified to species, and 40 per cent of all presumptive C. catla were hybrids between C. catla x C. cirrhosus and C. catla x L. rohita. In the case of C. cirrhosus, 37 per cent of the samples were C. cirrhosus x L. rohita hybrids. Thirty per cent of all presumptive L. rohita turned out to be hybrids between L. rohita x C. catla and L. rohita x C. cirrhosus. The high incidence of hybrids in C. catla might be responsible for slower growth of the fish in aquaculture
High level of hybridisation in three species of Indian major carps
Thirty individuals of each species of Indian major carps, i.e., Catla catla, Cirrhinus cirrhosus (C. mrigala) and Labeo rohita, obtained from a nursery near Mymensingh, Bangladesh were analysed by means of allozyme electrophoresis. Twenty-one loci were studied. Several loci revealed significant deviation from Hardy-Weinberg expectations caused by deficiency of heterozygotes, indicating Wahlund effects due to problems with species identification. Moreover, bimodal distributions of individual heterozygosity within the three putative species indicated hybridisation. This was confirmed using analysis of individual admixture proportions, as individuals misidentified to species and hybrids between species were observed. Furthermore, factorial correspondence analysis to visualize genetic relationships among individuals revealed three distinct groups containing misclassified individuals, along with some intermediate individuals interpreted as hybrids. Ten per cent of all C. catla and L. rohita had been erroneously identified to species, and 40 per cent of all presumptive C. catla were hybrids between C. catla x C. cirrhosus and C. catla x L. rohita. In the case of C. cirrhosus, 37 per cent of the samples were C. cirrhosus x L. rohita hybrids. Thirty per cent of all presumptive L. rohita turned out to be hybrids between L. rohita x C. catla and L. rohita x C. cirrhosus. The high incidence of hybrids in C. catla might be responsible for slower growth of the fish in aquaculture.Hybridization, DNA, Freshwater fish, Fish culture, Allozymes, Growth, Bangladesh, Catla catla, Cirrhinus cirrhosus, Cirrhinus mrigala, Labeo rohita
Predicting spring barley yield from variety-specific yield potential, disease resistance and straw length, and from environment-specific disease loads and weed pressure
Abstract For low-input crop production, well-characterised varieties increase the possibilities of managing diseases and weeds. This analysis aims at developing a framework for analyzing grain yield using external varietal information about disease resistance, weed competitiveness and yield potential and quantifying the impact of susceptibility grouping and straw length scores (as a measure for weed competitiveness) for predicting spring barley grain yield under variable biotic stress levels. The study
comprised 52 spring barley varieties and 17 environments, i.e., combinations of location, growing system and year. Individual varieties and their interactions with environments were analysed by factorial regression of grain yield on external variety information combined with observed environmental disease loads and weed pressure. The external information was based on the official Danish VCU testing. The most parsimonious models explained about 50% of the yield variation among varieties including genotypeenvironment interactions. Disease resistance characteristics of varieties, weighted with disease loads of powdery mildew, leaf rust and net blotch, respectively, had a highly significant influence on grain yield. The extend to which increased susceptibility resulted in increased yield losses in environments with high disease loads of the respective diseases was predicted. The effect of externally determined straw length scores, weighted with weed pressure, was weaker although significant for weeds with creeping growth habit. Higher grain yield was thus predicted for taller plants under weed pressure. The results are discussed in relation to the model ramework, impact of the considered traits and use of information from conventional variety testing in organic cropping systems
A Coupled-Channels Study of Coulomb Excitation
We study the effects of channel coupling in the excitation of
projectiles incident on heavy targets. The contribution to the excitation from
the Coulomb and the nuclear fields in peripheral collisions are considered. Our
results are compared with recent data on the excitation of the \halfm state
in projectiles. We show that the experimental results cannot be
explained, unless very unusual parameters are used.Comment: 8 pages, 2 Postscript figures available upon request, corrected
misprints in eqs. 2 and
Development of body mass and sexual size dimorphism in Danish red foxes (Vulpes vulpes)
<span class="fontstyle0">In this study, we examine the development of body mass and sexual size dimorphism (SSD) in 178 juvenile wild Danish red </span><span class="fontstyle0">foxes </span><span class="fontstyle0">from 99 litters </span><span class="fontstyle0">using </span><span class="fontstyle0">piecewise analyses of regression lines for age </span><span class="fontstyle2">versus</span><span class="fontstyle0"> weight</span><span class="fontstyle0">. When fox cubs are younger than 100 days, only slight (SSD=1.7%) and no significant difference</span><span class="fontstyle0"> (t-test: t=1.2, p=0.24) </span><span class="fontstyle0">was found in the mean weight of </span><span class="fontstyle0">males (2.03± kg) and females (1.93± kg), and</span><span class="fontstyle0"> no significant difference was found in the slope of regression lines </span><span class="fontstyle0">for </span><span class="fontstyle0">males and females </span><span class="fontstyle0">(F=0.97E-5, p = 0.99). In the growth period between 100 days of age and mating around 275 days of age, the regression line in males steepens more than that of females (difference in slopes, F=5.9, p<0.02) and the difference in mean weight of the sexes become highly significant (SSD=7.4%, difference in mean t=4.6, p=2.2E-5). After mating the growth curve levels off i.e. the slope of the regression lines for age </span><span class="fontstyle2">versus</span><span class="fontstyle0"> weight is not significantly different from zero. Yearly variation was revealed in the growth rate of juvenile foxes (difference in slope for males; F=3.9, p<0.01 and females; F=8.6, p<0.001). Conclusion: SSD in red foxes mainly develop </span><span class="fontstyle0">as a result of a faster grow rate in males </span><span class="fontstyle0">between indepency and maturity. Ontogony of red foxes may genetically be disposed to prevent males outcompeting females in the early stages of life (<100 days), when cubs are still fed by adults and the increase in SSD before mating, may be an adaption to selective forces benefitting larger males. </span><span class="fontstyle0">The growth rate of juvenile foxes of both sexes is influenced by environmental variation in different years.</span> <br /
Influence of the halo upon angular distributions for elastic scattering and breakup
The angular distributions for elastic scattering and breakup of halo nuclei
are analysed using a near-side/far-side decomposition within the framework of
the dynamical eikonal approximation. This analysis is performed for 11Be
impinging on Pb at 69 MeV/nucleon. These distributions exhibit very similar
features. In particular they are both near-side dominated, as expected from
Coulomb-dominated reactions. The general shape of these distributions is
sensitive mostly to the projectile-target interactions, but is also affected by
the extension of the halo. This suggests the elastic scattering not to be
affected by a loss of flux towards the breakup channel.Comment: 11 pages, 3 figures, accepted for publication in Phys. Lett.
Resonant Absorption as Mode Conversion?
Resonant absorption and mode conversion are both extensively studied
mechanisms for wave "absorption" in solar magnetohydrodynamics (MHD). But are
they really distinct? We re-examine a well-known simple resonant absorption
model in a cold MHD plasma that places the resonance inside an evanescent
region. The normal mode solutions display the standard singular resonant
features. However, these same normal modes may be used to construct a ray
bundle which very clearly undergoes mode conversion to an Alfv\'en wave with no
singularities. We therefore conclude that resonant absorption and mode
conversion are in fact the same thing, at least for this model problem. The
prime distinguishing characteristic that determines which of the two
descriptions is most natural in a given circumstance is whether the converted
wave can provide a net escape of energy from the conversion/absorption region
of physical space. If it cannot, it is forced to run away in wavenumber space
instead, thereby generating the arbitrarily small scales in situ that we
recognize as fundamental to resonant absorption and phase mixing. On the other
hand, if the converted wave takes net energy way, singularities do not develop,
though phase mixing may still develop with distance as the wave recedes.Comment: 23 pages, 8 figures, 2 tables; accepted by Solar Phys (July 9 2010
On collisional capture rates of irregular satellites around the gas-giant planets and the minimum mass of the solar nebula
We investigated the probability that an inelastic collision of planetesimals
within the Hill sphere of the Jovian planets could explain the presence and
orbits of observed irregular satellites. Capture of satellites via this
mechanism is highly dependent on not only the mass of the protoplanetary disk,
but also the shape of the planetesimal size distribution. We performed 2000
simulations for integrated time intervals Myr and found that, given
the currently accepted value for the minimum mass solar nebula and planetesimal
number density based upon the \citet{Nesvorny2003} and \citet{Charnoz2003} size
distribution , the collision rates for the different
Jovian planets range between and \gtrsim 170 \, \Myr^{-1} for
objects with radii, 1 \, \km \le r \le 10 \, \km. Additionally, we found that
the probability that these collisions remove enough orbital energy to yield a
bound orbit was and had very little dependence on the
relative size of the planetesimals. Of these collisions, the collision energy
between two objects was times the gravitational binding energy
for objects with radii km. We find that, capturing irregular
satellites via collisions between unbound objects can only account for of the observed population, hence can this not be the sole method of
producing irregular satellites.Comment: 11 pages 4 figures 1 table; This replaces a prior submission, which
contained some minor contradictions within the text accepted by MNRAS in
pres
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