126 research outputs found
A comparative study of two agamid lizards, Laudakia stellio and Pseudotrapelus sinaitus, in southern Sinai
The study compared habitat use and behaviour in two sympatric species of agamid lizard, Laudakia stellio and Pseudotrapelus sinaitus. Despite sharing the same habitat, the two species differed in their utilisation of microhabitats within it. Pseudotrapelus spent significantly longer on rocks compared to Laudakia. Pseudotrapelus showed evidence of heliothermic regulation, spending most of the time in the sun, but moving into the shade in the warmer afternoons. These varying temporal patterns may reflect differential thermoregulatory requirements between the two lizard species. Pseudotrapelus can change colour rapidly. There was no evidence of any thermoregulatory function in this ability; it is likely to be a form of social communication. Being brightly coloured was associated with behaviours implying increased conspicuousness: blue lizards were alert and vigilant for an average of 93% of each viewing session, compared to just 60% of the time in non-blue camouflaged lizards. The striking nature of the transitory blue colouration suggests it may have evolved for maximum salience, a trait common with signals. We simulated social encounters using blue model lizards and mirrors. Behavioural responses to these stimuli all involved colour changes, and support the social-signaling hypothesis
Recommended from our members
Functional Imaging of the Outer Retinal Complex using High Fidelity Imaging Retinal Densitometry
We describe a new technique, high fidelity Imaging Retinal Densitometry (IRD), which probes the functional integrity of the outer retinal complex. We demonstrate the ability of the technique to map visual pigment optical density and synthesis rates in eyes with and without macular disease. A multispectral retinal imaging device obtained precise measurements of retinal reflectance over space and time. Data obtained from healthy controls and 5 patients with intermediate AMD, before and after photopigment bleaching, were used to quantify visual pigment metrics. Heat maps were plotted to summarise the topography of rod and cone pigment kinetics and descriptive statistics conducted to highlight differences between those with and without AMD. Rod and cone visual pigment synthesis rates in those with AMD (v = 0.043 SD 0.019 min-1 and v = 0.119 SD 0.046 min-1, respectively) were approximately half those observed in healthy controls (v = 0.079 SD 0.024 min-1 for rods and v = 0.206 SD 0.069 min-1 for cones). By mapping visual pigment kinetics across the central retina, high fidelity IRD provides a unique insight into outer retinal complex function. This new technique will improve the phenotypic characterisation, diagnosis and treatment monitoring of various ocular pathologies, including AMD
Flow Phase Diagram for the Helium Superfluids
The flow phase diagram for He II and He-B is established and discussed
based on available experimental data and the theory of Volovik [JETP Letters
{\bf{78}} (2003) 553]. The effective temperature - dependent but scale -
independent Reynolds number , where
and are the mutual friction parameters and the superfluid Reynolds
number characterizing the circulation of the superfluid component in units of
the circulation quantum are used as the dynamic parameters. In particular, the
flow diagram allows identification of experimentally observed turbulent states
I and II in counterflowing He II with the turbulent regimes suggested by
Volovik.Comment: 2 figure
The Resolved Structure and Dynamics of an Isolated Dwarf Galaxy: A VLT and Keck Spectroscopic Survey of WLM
We present spectroscopic data for 180 red giant branch stars in the isolated
dwarf irregular galaxy WLM. Observations of the Calcium II triplet lines in
spectra of RGB stars covering the entire galaxy were obtained with FORS2 at the
VLT and DEIMOS on Keck II allowing us to derive velocities, metallicities, and
ages for the stars. With accompanying photometric and radio data we have
measured the structural parameters of the stellar and gaseous populations over
the full galaxy. The stellar populations show an intrinsically thick
configuration with . The stellar rotation in WLM is
measured to be km s, however the ratio of rotation to
pressure support for the stars is , in contrast to the gas
whose ratio is seven times larger. This, along with the structural data and
alignment of the kinematic and photometric axes, suggests we are viewing WLM as
a highly inclined oblate spheroid. Stellar rotation curves, corrected for
asymmetric drift, are used to compute a dynamical mass of M at the half light radius (
pc). The stellar velocity dispersion increases with stellar age in a manner
consistent with giant molecular cloud and substructure interactions producing
the heating in WLM. Coupled with WLM's isolation, this suggests that the
extended vertical structure of its stellar and gaseous components and increase
in stellar velocity dispersion with age are due to internal feedback, rather
than tidally driven evolution. These represent some of the first observational
results from an isolated Local Group dwarf galaxy which can offer important
constraints on how strongly internal feedback and secular processes modulate SF
and dynamical evolution in low mass isolated objects.Comment: 14 Pages, 17 figures, 3 tables. Accepted for publication in Ap
Investigating The Possible Anomaly Between Nebular and Stellar Oxygen Abundances in the Dwarf Irregular Galaxy WLM
We obtained new optical spectra of 13 H II regions in WLM with EFOSC2; oxygen
abundances are derived for nine H II regions. The temperature-sensitive [O III]
4363 emission line was measured in two bright H II regions HM7 and HM9. The
direct oxygen abundances for HM7 and HM9 are 12+log(O/H) = 7.72 +/- 0.04 and
7.91 +/- 0.04, respectively. We adopt a mean oxygen abundance of 12+log(O/H) =
7.83 +/- 0.06. This corresponds to [O/H] = -0.83 dex, or 15% of the solar
value. In H II regions where [O III] 4363 was not measured, oxygen abundances
derived with bright-line methods are in general agreement with direct values of
the oxygen abundance to an accuracy of about 0.2 dex. In general, the present
measurements show that the H II region oxygen abundances agree with previous
values in the literature. The nebular oxygen abundances are marginally
consistent with the mean stellar magnesium abundance ([Mg/H] = -0.62). However,
there is still a 0.62 dex discrepancy in oxygen abundance between the nebular
result and the A-type supergiant star WLM15 ([O/H] = -0.21). Non-zero reddening
values derived from Balmer line ratios were found in H II regions near a second
H I peak. There may be a connection between the location of the second H I
peak, regions of higher extinction, and the position of WLM15 on the eastern
side of the galaxy.Comment: Accepted, Ap.J.; 19 pages (AASTeX 5.2) with 6 figures. Full paper
with color figures at http://www.astro.umn.edu/~hlee
A Spitzer/IRAC Census of the Asymptotic Giant Branch Populations in Local Group Dwarfs. I. WLM
We present Spitzer/IRAC observations at 3.6 and 4.5 microns along with
optical data from the Local Group Galaxies Survey to investigate the evolved
stellar population of the Local Group dwarf irregular galaxy WLM. These
observations provide a nearly complete census of the asymptotic giant branch
(AGB) stars. We find 39% of the infrared-detected AGB stars are not detected in
the optical data, even though our 50% completeness limit is three magnitudes
fainter than the red giant branch tip. An additional 4% of the
infrared-detected AGBs are misidentified in the optical, presumably due to
reddening by circumstellar dust. We also compare our results with those of a
narrow-band optical carbon star survey of WLM, and find the latter study
sensitive to only 18% of the total AGB population. We detect objects with
infrared fluxes consistent with them being mass-losing AGB stars, and derive a
present day total mass-loss rate from the AGB stars of 0.7-2.4 x 10^(-3) solar
masses per year. The distribution of mass-loss rates and bolometric
luminosities of AGBs and red supergiants are very similar to those in the LMC
and SMC and the empirical maximum mass-loss rate observed in the LMC and SMC is
in excellent agreement with our WLM data.Comment: Accepted by ApJ, 34 pages, 13 figures, version with high-resolution
figures available at: http://webusers.astro.umn.edu/~djackson
The Expression and Localization of N-Myc Downstream-Regulated Gene 1 in Human Trophoblasts
The protein N-Myc downstream-regulated gene 1 (NDRG1) is implicated in the regulation of cell proliferation, differentiation, and cellular stress response. NDRG1 is expressed in primary human trophoblasts, where it promotes cell viability and resistance to hypoxic injury. The mechanism of action of NDRG1 remains unknown. To gain further insight into the intracellular action of NDRG1, we analyzed the expression pattern and cellular localization of endogenous NDRG1 and transfected Myc-tagged NDRG1 in human trophoblasts exposed to diverse injuries. In standard conditions, NDRG1 was diffusely expressed in the cytoplasm at a low level. Hypoxia or the hypoxia mimetic cobalt chloride, but not serum deprivation, ultraviolet (UV) light, or ionizing radiation, induced the expression of NDRG1 in human trophoblasts and the redistribution of NDRG1 into the nucleus and cytoplasmic membranes associated with the endoplasmic reticulum (ER) and microtubules. Mutation of the phosphopantetheine attachment site (PPAS) within NDRG1 abrogated this pattern of redistribution. Our results shed new light on the impact of cell injury on NDRG1 expression patterns, and suggest that the PPAS domain plays a key role in NDRG1's subcellular distribution. © 2013 Shi et al
<i>ATP5PO </i>levels regulate enteric nervous system development in zebrafish, linking Hirschsprung disease to Down Syndrome
Hirschsprung disease (HSCR) is a complex genetic disorder characterized by the absence of enteric nervous system (ENS) in the distal region of the intestine. Down Syndrome (DS) patients have a >50-fold higher risk of developing HSCR than the general population, suggesting that overexpression of human chromosome 21 (Hsa21) genes contribute to HSCR etiology. However, identification of responsible genes remains challenging. Here, we describe a genetic screening of potential candidate genes located on Hsa21, using the zebrafish. Candidate genes were located in the DS-HSCR susceptibility region, expressed in the human intestine, were known potential biomarkers for DS prenatal diagnosis, and were present in the zebrafish genome. With this approach, four genes were selected: RCAN1, ITSN1, ATP5PO and SUMO3. However, only overexpression of ATP5PO, coding for a component of the mitochondrial ATPase, led to significant reduction of ENS cells. Paradoxically, in vitro studies showed that overexpression of ATP5PO led to a reduction of ATP5PO protein levels. Impaired neuronal differentiation and reduced mitochondrial ATP production, were also detected in vitro, after overexpression of ATP5PO in a neuroblastoma cell line. Finally, epistasis was observed between ATP5PO and ret, the most important HSCR gene. Taken together, our results identify ATP5PO as the gene responsible for the increased risk of HSCR in DS patients in particular if RET variants are also present, and show that a balanced expression of ATP5PO is required for normal ENS development.</p
- …