95 research outputs found
Artificial selection reveals the energetic expense of producing larger eggs
This is the final version of the article. Available from BioMed Central via the DOI in this record.BACKGROUND: The amount of resources provided by the mother before birth has important and long-lasting effects on offspring fitness. Despite this, there is a large amount of variation in maternal investment seen in natural populations. Life-history theory predicts that this variation is maintained through a trade-off between the benefits of high maternal investment for the offspring and the costs of high investment for the mother. However, the proximate mechanisms underlying these costs of reproduction are not well understood. Here we used artificial selection for high and low maternal egg investment in a precocial bird, the Japanese quail (Coturnix japonica) to quantify costs of maternal reproductive investment. RESULTS: We show that females from the high maternal investment lines had significantly larger reproductive organs, which explained their overall larger body mass, and resulted in a higher resting metabolic rate (RMR). Contrary to our expectations, this increase in metabolic activity did not lead to a higher level of oxidative damage. CONCLUSIONS: This study is the first to provide experimental evidence for metabolic costs of increased per offspring investment.The study was financially supported by the Swiss National Science Foundation (PP00P3 128386 and 458 PP00P3 157455 to BT)
Cyst-Wall-Protein-1 is fundamental for Golgi-like organelle neogenesis and cyst-wall biosynthesis in Giardia lamblia
The genome of the protozoan parasite Giardia lamblia is organized in two diploid nuclei, which has so far precluded complete analysis of gene function. Here we use a previously developed Cre/loxP-based knock-out and selection marker salvage strategy in the human-derived isolate WB-C6 to eliminate all four copies of the Cyst-Wall-Protein-1 locus (CWP1). Because these loci are silenced in proliferating trophozoites and highly expressed only in encysting cells, CWP1 ablation allows functional characterization of a conditional phenotype in parasites induced to encyst. We show that encysting Îcwp1 cells are unable to establish the stage-regulated trafficking machinery with Golgi-like encystation-specific vesicles required for cyst-wall formation but show morphological hallmarks of cyst development and karyokinesis. This âpseudocystâ phenotype is rescued by transfection of Îcwp1 cells with an episomally maintained CWP1 expression vector. Genome editing in genera Giardia and Trypanosoma are the only reported examples addressing questions on pathogen transmission within the Excavata supergroup
Determining the extragalactic extinction law with SALT. II. Additional sample
We present new results from an on-going programme to study the dust
extragalactic extinction law in E/S0 galaxies with dust lanes with the Southern
African Large Telescope (SALT) during its performance-verification phase. The
wavelength dependence of the dust extinction for seven galaxies is derived in
six spectral bands ranging from the near-ultraviolet atmospheric cutoff to the
near-infrared. The derivation of an extinction law is performed by fitting
model galaxies to the unextinguished parts of the image in each spectral band,
and subtracting from these the actual images. We compare our results with the
derived extinction law in the Galaxy and find them to run parallel to the
Galactic extinction curve with a mean total-to-selective extinction value of
2.71+-0.43. We use total optical extinction values to estimate the dust mass
for each galaxy, compare these with dust masses derived from IRAS measurements,
and find them to range from 10^4 to 10^7 Solar masses. We study the case of the
well-known dust-lane galaxy NGC2685 for which HST/WFPC2 data is available to
test the dust distribution on different scales. Our results imply a scale-free
dust distribution across the dust lanes, at least within ~1 arcsec (~60 pc)
regions.Comment: 11 pages, 7 figures, 3 tables. Accepted for publication in MNRAS.
R-band contour maps and B-R colour-index maps are low-resolution versions of
those used in the MNRAS versio
Kinematics of elliptical galaxies with a diffuse dust component
Observations show that early-type galaxies contain a considerable amount of
interstellar dust, most of which is believed to exist as a diffusely
distributed component. We construct a four-parameter elliptical galaxy model in
order to investigate the effects of such a smooth absorbing component on the
projection of kinematic quantities, such as the line profiles and their
moments. We investigate the dependence on the optical depth and on the dust
geometry. Our calculations show that both the amplitude and the morphology of
these quantities can be significantly affected. Dust effects should therefore
be taken in consideration when interpreting photometric and kinematic
properties, and correlations that utilize these quantities.Comment: 12 pages, 9 figures, accepted for publication in MNRA
Properties of dust in early-type galaxies
We report optical extinction properties of dust for a sample of 26 early-type
galaxies based on the analysis of their multicolour CCD observations. The
wavelength dependence of dust extinction for these galaxies is determined and
the extinction curves are found to run parallel to the Galactic extinction
curve, which implies that the properties of dust in the extragalactic
environment are quite similar to those of the Milky Way. For the sample
galaxies, value of the parameter , the ratio of total extinction in
band to selective extinction in & bands, lies in the range 2.03 - 3.46
with an average of 3.02, compared to its canonical value of 3.1 for the Milky
Way. A dependence of on dust morphology of the host galaxy is also
noticed in the sense that galaxies with a well defined dust lane show tendency
to have smaller values compared to the galaxies with disturbed dust
morphology. The dust content of these galaxies estimated using total optical
extinction is found to lie in the range to 10^6 \rm M_{\sun}, an order
of magnitude smaller than those derived from IRAS flux densities, indicating
that a significant fraction of dust intermixed with stars remains undetected by
the optical method. We examine the relationship between dust mass derived from
IRAS flux and the X-ray luminosity of the host galaxies.The issue of the origin
of dust in early-type galaxies is also discussed.Comment: 12 pages, 6 figures. Accepted for publication in Astronomy &
Astrophysic
Determining the extragalactic extinction law with SALT
We present CCD imaging observations of early-type galaxies with dark lanes
obtained with the Southern African Large Telescope (SALT) during its
performance-verification phase. We derive the extinction law by the
extragalactic dust in the dark lanes in the spectral range 1.11mu m^{-1} <
lambda^{-1} < 2.94 mu m^{-1} by fitting model galaxies to the unextinguished
parts of the image, and subtracting from these the actual images. We find that
the extinction curves run parallel to the Galactic extinction curve, which
implies that the properties of dust in the extragalactic enviroment are similar
to those of the Milky Way. The ratio of the total V band extinction to the
selective extinction between the V and B bands is derived for each galaxy with
an average of 2.82+-0.38, compared to a canonical value of 3.1 for the Milky
Way. The similar values imply that galaxies with well-defined dark lanes have
characteristic dust grain sizes similar to those of Galactic dust.Comment: 20 pages, 15 figures and 4 tables. Accepted for publication in MNRA
RXTE monitoring of Centaurus A
We report on the analysis from ~110 ks of X-ray observations of Centaurus A
carried out with the Proportional Counter Array (PCA) and the High Energy X-ray
Timing Experiment (HEXTE) instruments on Rossi X-ray Timing Explorer (RXTE)
during three monitoring campaigns over the last 4 years (10 ks in 1996, 74 ks
in 1998, and 25 ks in 2000). The joint PCA/HEXTE X-ray spectrum can be well
described by a heavily absorbed power law with photon index 1.8 and a narrow
iron line due to fluorescence of cold matter. The measured column depth
decreased by about 30% between 1996 and 2000, while the detected 2-10 keV
continuum flux remained constant between 1996 and 1998, but increased by 60% in
2000. Since in all three observations the iron line flux did not vary, a
corresponding decrease in equivalent width was noted. No appreciable evidence
for a reflection continuum in the spectrum was detected. We present the
interpretation of the iron line strength through Monte Carlo computations of
various geometries. No significant temporal variability was found in Cen A at
time scales from days to tens of minutes.Comment: 7 pages, 4 figures. Accepted for publication in A&
Does transient increase in axial length during accommodation attenuate with age?
Background: The aim was to profile transient accommodative axial length (AXL) changes from early adulthood to advanced presbyopia and to determine whether any differences exist between the responses of myopic and emmetropic individuals. Methods: Ocular biometry was measured by the LenStar biometer (Haag-Streit, Switzerland) in response to 0.00, 3.00 and 4.50 D accommodative stimuli in 35 emmetropes and 37 myopes, aged 18 to 60 years. All results were corrected to reduce errors arising from the increase in crystalline lens thickness with accommodation. Accommodative responses were measured sequentially by the WAM 5500 Auto Ref/Keratometer (Grand Seiko, Japan). Results: AXL increased significantly with accommodation (p<0.001), with a mean corrected AXL elongation of 2 ± 18 ”m and 8 ± 16 ”m observed at 3.00 D and 4.50 D, respectively. The magnitude of accommodative AXL change was not dependent on refractive error classification (p=0.959), however a significant reduction in the magnitude and variance of AXL change was evident after 43-44 years of age (p<0.002). Conclusion: The negative association between transient AXL elongation and age, in combination with reduced variance of data after age 43-44 years, is consistent with a significant increase in posterior ocular rigidity, which may be influential in the development of presbyopia
Barriers to identifying eating disorders in pregnancy and in the postnatal period: a qualitative approach.
BACKGROUND: Eating Disorders (ED) are mental health disorders that typically effect women of childbearing age and are associated with adverse maternal and infant outcomes. UK healthcare guidance recommends routine enquiry for current and past mental illness in antenatal and postnatal care for all women, and that pregnant women with a known ED are offered enhanced monitoring and support. Midwives and health visitors are ideally placed to identify and support women with ED as they are often the primary point of contact during the antenatal and postnatal periods. However, research on the barriers to identifying ED in the perinatal period is limited. This study aimed to understand the barriers to disclosure and identification of ED in pregnancy and postnatally as perceived by women with past or current ED, and midwives and health visitors working in the UK National Health Service. METHODS: Two studies were undertaken: mixed-measures survey of pregnant and postnatal women with current or past ED; focus groups with student and qualified midwives and health visitors. RESULTS: Five themes emerged on the barriers to disclosure in pregnancy as perceived by women: stigma, lack of opportunity, preference for self-management, current ED symptomatology and illness awareness. Four themes were identified on the barriers to identification of ED in pregnancy and in the postnatal period as perceived by health professionals: system constraints, recognition of role, personal attitudes, and stigma and taboo. CONCLUSIONS: Several barriers to the identification of ED during and after pregnancy were described, the main factors were stigma and poor professional training. Perinatal mental health is becoming increasingly prioritised within national policy initiatives; however, ED continue to be neglected and increased awareness is needed. Similarly, clinical guidance aimed at responding to the rising prevalence of obesity focus on changing nutrition but not on assessing for the presence of ED behaviours that might be affecting nutrition. Improving education and training for health professionals may contribute to reducing stigma and increase confidence in identifying ED. The barriers identified in this research need to be addressed if recognition and response to women with ED during the perinatal period is to improve
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