183 research outputs found
Electrophysiological and molecular genetic evidence for sympatrically occuring cryptic species in African weakly electric fishes (Teleostei : Mormyridae : Campylomormyrus)
No full textFor two sympatric species of African weakly electric fish, Campylomormyrus tamandua and Campylomormyrus numenius, we monitored ontogenetic differentiation in electric organ discharge (EOD) and established a molecular phylogeny, based on 2222 bp from cytochrome b, the S7 ribosomal protein gene, and four flanking regions of unlinked microsatellite loci. In C tamandua, there is one common EOD type, regardless of age and sex, whereas in C numenius we were able to identify three different male adult EOD waveform types, which emerged from a single common EOD observed in juveniles. Two of these EOD types formed well supported clades in our phylogenetic analysis. In an independent line of evidence, we were able to affirm the classification into three groups by microsatellite data. The correct assignment and the high pairwise FST values support our hypothesis that these groups are reproductively isolated. We propose that in C numenius there are cryptic species, hidden behind similar and, at least as juveniles, identical morphs. (c) 2005 Elsevier Inc. All rights reserved
Adaptive radiation in African weakly electric fish (Teleostei : Mormyridae : Campylomormyrus): a combined molecular and morphological approach
No full textWe combined multiple molecular markers and geometric morphometrics to revise the current taxonomy and to build a phylogenetic hypothesis for the African weakly electric fish genus Campylomormyrus. Genetic data (2039 bp DNA sequence of mitochondrial cytochrome b and nuclear S7 genes) on 106 specimens support the existence of at least six species occurring in sympatry. We were able to further confirm these species by microsatellite analysis at 16 unlinked nuclear loci and landmark-based morphometrics. We assigned them to nominal taxa by comparisons to type specimens of all Campylomormyrus species recognized so far. Additionally, we showed that the shape of the elongated trunk-like snout is the major source of morphological differentiation among them. This finding suggests that the radiation of this speciose genus might have been driven by adaptation to different food sources
The evolution of the luminosity functions in the FORS Deep Field from low to high redshift. I. The blue bands
No full textWe use the very deep and homogeneous I-band selected
dataset of the FORS Deep Field (FDF) to trace the evolution of the
luminosity function over the redshift range .
We show that the FDF I-band selection down to misses
of the order of 10% of the galaxies that would be detected in a
K-band selected survey with magnitude limit (like
FIRES). Photometric redshifts for 5558 galaxies are estimated based
on the photometry in 9 filters (U, B, Gunn g, R, I, SDSS z, J, K and a special filter centered at 834 nm). A comparison with 362 spectroscopic redshifts shows that the achieved accuracy of the
photometric redshifts is
with only ~1% outliers. This allows us to derive luminosity
functions with a reliability similar to spectroscopic surveys. In
addition, the luminosity functions can be traced to objects of lower
luminosity which generally are not accessible to spectroscopy. We
investigate the evolution of the luminosity functions evaluated in
the restframe UV (1500 Å and 2800 Å), u', B, and g' bands.
Comparison with results from the literature shows the reliability of
the derived luminosity functions. Out to redshifts of
the data are consistent with a slope of the luminosity function
approximately constant with redshift, at a value of
in the UV (1500 Å, 2800 Å) as well as u', and
in the blue (g', B). We do not see evidence for a very steep slope
() in the UV at and favoured by other
authors. There may be a tendency for the faint-end slope to become
shallower with increasing redshift but the effect is marginal. We
find a brightening of and a decrease of with
redshift for all analyzed wavelengths. The effect is systematic and
much stronger than what can be expected to be caused by cosmic
variance seen in the FDF. The evolution of and
from to is well described by the simple approximations
and for and . The
evolution is very pronounced at shorter wavelengths
(, and for 1500 Å rest wavelength) and
decreases systematically with increasing wavelength, but is also
clearly visible at the longest wavelength investigated here
(, and for g'). Finally we show a
comparison with semi-analytical galaxy formation models
The evolution of the luminosity functions in the FORS deep field from low to high redshift - II. The red bands
No full textWe present the redshift evolution of the restframe galaxy
luminosity function (LF) in the red r', i', and z' bands, as derived
from the FORS Deep Field (FDF), thus extending our earlier results
to longer wavelengths. Using the deep and
homogeneous I-band selected dataset of the FDF, we were able to follow
the red LFs over the redshift range . The
results are based on photometric redshifts for 5558 galaxies derived
from the photometry in 9 filters and achieving an accuracy of
with only ~%
outliers. A comparison with results from the literature shows the
reliability of the derived LFs. Because of the depth of the FDF, we
can give relatively tight constraints on the faint-end slope α of the LF; the faint-end of the red LFs does not show a
large redshift evolution and is compatible within to with a constant slope over the redshift range 0.5
\la z \la 2.0. Moreover, the slopes in r', i', and z' are
very similar to a best-fitting value of
for the combined bands. There is a clear trend of α to
steepen with increasing wavelength:
. We
subdivided our galaxy sample into four SED types and determined the
contribution of a typical SED type to the overall LF. We show that
the wavelength dependence of the LF slope can be explained by the
relative contribution of different SED-type LFs to the overall LF,
as different SED types dominate the LF in the blue and red bands.
Furthermore we also derived and analyzed the luminosity density
evolution of the different SED types up to .
We investigated the evolution of and by means of
the redshift parametrization and .
Based on the FDF data, we found only a mild brightening
of (, and ) and
a decreasing () with increasing
redshift. Therefore, from to
the characteristic luminosity
increases by ~0.8, ~0.4, and ~0.4 mag in
the r', i', and z' bands, respectively. Simultaneously the
characteristic density decreases by about 40% in all analyzed
wavebands.
A comparison of the LFs with semi-analytical galaxy formation models
by Kauffmann et al. (1999) shows a similar result to the blue bands:
the semi-analytical models predict LFs that describe the data at
low redshift very well, but show growing disagreement with
increasing redshifts.
Low Temperature Physics V. 29, I. 03
No full textLow Temperature Physics -- March 2003
Volume 29, Issue 3, pp. 163-273
Electronically induced phenomena: low temperature aspects (Preface)
P. Feulner and E. Savchenko
Full Text: PDF (18 kB)
Particle transport phenomena in low-temperature solids (Review)
M. Bargheer and N. Schwentner
Full Text: PDF (295 kB)
Coherent motion and anomalous transport properties of exciton and hole polarons with intrinsic vibrational structure
A. M. Ratner
Full Text: PDF (147 kB)
Excess electron transport in cryoobjects
D. G. Eshchenko, V. G. Storchak, J. H. Brewer, S. P. Cottrell, and S. F. J. Cox
Full Text: PDF (141 kB)
Low-temperature electron transport on semiconductor surfaces
M. Lastapis, D. Riedel, A. Mayne, K. Bobrov, and G. Dujardin
Full Text: PDF (381 kB)
Reactions induced by low energy electrons in cryogenic films (Review)
A. D. Bass and L. Sanche
Full Text: PDF (229 kB)
Effects of electron irradiation on structure and bonding of SF6 on Ru(0001)
N. S. Faradzhev, D. O. Kusmierek, B. V. Yakshinskiy, and T. E. Madey
Full Text: PDF (264 kB)
Soft landing of size-selected clusters in rare gas matrices
J. T. Lau, W. Wurth, H.-U. Ehrke, and A. Achleitner
Full Text: PDF (93 kB)
Element-specific and site-specific ion desorption from adsorbed molecules by deep core-level photoexcitation at the K-edges
Y. Baba
Full Text: PDF (552 kB)
Ion desorption from molecules condensed at low temperature: A study with electron-ion coincidence spectroscopy combined with synchrotron radiation (Review)
Kazuhiko Mase, Mitsuru Nagasono, Shin-ichiro Tanaka, Tetsuji Sekitani, and Shin-ichi Nagaoka
Full Text: PDF (1124 kB)
Absolute yields of the exciton-induced desorption at the surface of solid rare gases
I. Arakawa, T. Adachi, T. Hirayama, and M. Sakurai
Full Text: PDF (143 kB)
Biexcitons in solid neon
P. Wiethoff, B. Kassühlke, D. Menzel, and P. Feulner
Full Text: PDF (74 kB)
Exciton-induced lattice defect formation
E. V. Savchenko, A. N. Ogurtsov, and G. Zimmerer
Full Text: PDF (61 kB)Archived web conten
High parasite diversity maintained after an alga-virus coevolutionary arms race.
No full textArms race dynamics are a common outcome of host-parasite coevolution. While they can theoretically be maintained indefinitely, realistic arms races are expected to be finite. Once an arms race has ended, for example due to the evolution of a generalist resistant host, the system may transition into coevolutionary dynamics that favor long-term diversity. In microbial experiments, host-parasite arms races often transition into a stable coexistence of generalist resistant hosts, (semi-)susceptible hosts, and parasites. While long-term host diversity is implicit in these cases, parasite diversity is usually overlooked. In this study, we examined parasite diversity after the end of an experimental arms race between a unicellular alga (Chlorella variabilis) and its lytic virus (PBCV-1). First, we isolated virus genotypes from multiple time points from two replicate microcosms. A time-shift experiment confirmed that the virus isolates had escalating host ranges, i.e. that the arms races had occurred. We then examined the phenotypic and genetic diversity of virus isolates from the post-arms race phase. Post-arms race virus isolates had diverse host ranges, survival probabilities, and growth rates; they also clustered into distinct genetic groups. Importantly, host range diversity was maintained throughout the post-arms race phase, and the frequency of host range phenotypes fluctuated over time. We hypothesize that this dynamic polymorphism was maintained by a combination of fluctuating selection and demographic stochasticity. Together with previous work in prokaryotic systems, our results link experimental observations of arms races to natural observations of long-term host and parasite diversity
Genomic architecture of adaptive radiation and hybridization in Alpine whitefish
No full textAdaptive radiations represent some of the most remarkable explosions of diversification across the tree of life. However, the constraints to rapid diversification and how they are sometimes overcome, particularly the relative roles of genetic architecture and hybridization, remain unclear. Here, we address these questions in the Alpine whitefish radiation, using a whole-genome dataset that includes multiple individuals of each of the 22 species belonging to six ecologically distinct ecomorph classes across several lake-systems. We reveal that repeated ecological and morphological diversification along a common environmental axis is associated with both genome-wide allele frequency shifts and a specific, larger effect, locus, associated with the gene edar. Additionally, we highlight the possible role of introgression between species from different lake-systems in facilitating the evolution and persistence of species with unique trait combinations and ecology. These results highlight the importance of both genome architecture and secondary contact with hybridization in fuelling adaptive radiation
Strong selection and high mutation supply characterize experimental Chlorovirus evolution
No full textCharacterizing how viruses evolve expands our understanding of the underlying fundamental processes, such as mutation, selection and drift. One group of viruses whose evolution has not yet been extensively studied is the Phycodnaviridae, a globally abundant family of aquatic large double-stranded (ds)DNA (dsDNA) viruses. Here we studied the evolutionary change of Paramecium bursaria chlorella virus 1 during experimental coevolution with its algal host. We used pooled genome sequencing of six independently evolved populations to characterize genomic change over five time points. Across six experimental replicates involving either strong or weak demographic fluctuations, we found single nucleotide polymorphisms (SNPs) at sixty-seven sites. The occurrence of genetic variants was highly repeatable, with just two of the SNPs found in only a single experimental replicate. Three genes A122/123R, A140/145R and A540L showed an excess of variable sites, providing new information about potential targets of selection during Chlorella–Chlorovirus coevolution. Our data indicated that the studied populations were not mutation-limited and experienced strong positive selection. Our investigation highlighted relevant processes governing the evolution of aquatic large dsDNA viruses, which ultimately contributes to a better understanding of the functioning of natural aquatic ecosystems
A LEED determination of the structures of Ru(001) and of CO/Ru(001)−(√3 × √3)R30°
No full textThe structures of Ru(001) and of the √3 × √3 R30° overlayer of CO on Ru(001) have been determined by LEED I–V measurements and comparison to calculations. Special attention was paid to accurate angular alignment, selection of a well-ordered portion of the surface, and avoidance of beam-induced changes of the CO layer. Five orders of reflexes over a range of 300 eV each were used for the clean surface and 7 orders over 200 eV each for the CO superstructure. For the clean surface, a slight contraction of the first layer spacing (by 2%) was found which gave r-factors of 0.04 (Zanazzi-Jona) and 0.16 (Pendry) for 5 non-degenerate beams. For the CO structure the most probable geometry is the on-top site with spacings d(Ru---C) = 2.0 ± 0.1 Åandd(C---O) = 1.10 ± 0.1 Å (rZJ = 0.21; rP = 0.51). The two threefold hollow and the bridge sites can be clearly excluded
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